ASTM E709-21

Standard Guide for Magnetic Particle Testing

SIGNIFICANCE AND USE
5.1 The magnetic particle method of nondestructive testing indicates the presence of surface and near-surface discontinuities in materials that can be magnetized (ferromagnetic). This method can be used for production examination of parts/components or structures and for field applications where portability of equipment and accessibility to the area to be examined are factors. The ability of the method to find small discontinuities can be enhanced by using fluorescent particles suspended in a suitable vehicle and by introducing a magnetic field of the proper strength whose orientation is as close as possible to 90° to the direction of the suspected discontinuity (see 4.3.2). A smoother surface or a pulsed current improves mobility of the magnetic particles under the influence of the magnetic field to collect on the surface where magnetic flux leakage occurs.
SCOPE
1.1 This guide2 covers techniques for both dry and wet magnetic particle testing, a nondestructive method for detecting cracks and other discontinuities at or near the surface in ferromagnetic materials. Magnetic particle testing may be applied to raw material, semifinished material (billets, blooms, castings, and forgings), finished material and welds, regardless of heat treatment or lack thereof. It is useful for preventive maintenance testing.  
1.1.1 This guide is intended as a reference to aid in the preparation of specifications/standards, procedures and techniques.  
1.2 This guide is also a reference that may be used as follows:  
1.2.1 To establish a means by which magnetic particle testing, procedures recommended or required by individual organizations, can be reviewed to evaluate their applicability and completeness.  
1.2.2 To aid in the organization of the facilities and personnel concerned in magnetic particle testing.  
1.2.3 To aid in the preparation of procedures dealing with the examination of materials and parts. This guide describes magnetic particle testing techniques that are recommended for a great variety of sizes and shapes of ferromagnetic materials and widely varying examination requirements. Since there are many acceptable differences in both procedure and technique, the explicit requirements should be covered by a written procedure (see Section 21).  
1.3 This guide does not indicate, suggest, or specify acceptance standards for parts/pieces examined by these techniques. It should be pointed out, however, that after indications have been produced, they must be interpreted or classified and then evaluated. For this purpose there should be a separate code, specification, or a specific agreement to define the type, size, location, degree of alignment and spacing, area concentration, and orientation of indications that are unacceptable in a specific part versus those which need not be removed before part acceptance. Conditions where rework or repair is not permitted should be specified.  
1.4 This guide describes the use of the following magnetic particle method techniques.  
1.4.1 Dry magnetic powder (see 8.4),  
1.4.2 Wet magnetic particle (see 8.5),  
1.4.3 Magnetic slurry/paint magnetic particle (see 8.5.7), and  
1.4.4 Polymer magnetic particle (see 8.5.8).  
1.5 Personnel Qualification—Personnel performing examinations in accordance with this guide should be qualified and certified in accordance with ASNT Recommended Practice No. SNT-TC-1A, ANSI/ASNT Standard CP-189, NAS 410, or as specified in the contract or purchase order.  
1.6 Nondestructive Testing Agency—If a nondestructive testing agency as described in Specification E543 is used to perform the examination, the nondestructive testing agency should meet the requirements of Specification E543.  
1.7 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.8 Warning—...

General Information

• Status: Published
• Publication Date: 31-May-2021
• ICS: 77.040.20 - Non-destructive testing of metals
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.03 - Liquid Penetrant and Magnetic Particle Methods

Relations

• Refers: ASTM D445-24 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 01-Apr-2024
• Refers: ASTM E1316-24 - Standard Terminology for <?Pub Dtl?>Nondestructive Examinations
• Effective Date: 01-Feb-2024
• Refers: ASTM D445-23 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 01-Nov-2023
• Refers: ASTM D93-20 - Standard Test Methods for Flash Point by Pensky-Martens Closed Cup Tester
• Effective Date: 01-Aug-2020
• Refers: ASTM E1316-19b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2019
• Refers: ASTM E1316-19 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Mar-2019
• Refers: ASTM E1316-18 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jan-2018
• Refers: ASTM E1316-17a - Standard Terminology for Nondestructive Examinations
• Effective Date: 15-Jun-2017
• Refers: ASTM E1316-17 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2017
• Refers: ASTM D445-16 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 15-Dec-2016
• Refers: ASTM E1316-16a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Aug-2016
• Refers: ASTM E3024/E3024M-16 - Standard Practice for Magnetic Particle Testing for General Industry
• Effective Date: 01-Jul-2016
• Refers: ASTM E1444/E1444M-16 - Standard Practice for Magnetic Particle Testing
• Effective Date: 01-Jun-2016
• Refers: ASTM E1316-16 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2016
• Refers: ASTM E1316-15a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2015

Overview

ASTM E709-21: Standard Guide for Magnetic Particle Testing provides comprehensive methodologies for applying magnetic particle testing (MT or MPT), a widely-used nondestructive testing (NDT) process for detecting surface and near-surface discontinuities in ferromagnetic materials. Developed by ASTM, this guide supports both production and field applications, emphasizing standardized procedures, reliable interpretation, and ensuring personnel and agency competency.

Magnetic particle testing is essential for safety and integrity in manufacturing, fabrication, and maintenance across multiple industries. ASTM E709-21 ensures consistent and effective testing, regardless of the material preparation state or configuration, and allows for adaptability in various operational environments.

Key Topics

• Applicability

  • Covers techniques for dry, wet, slurry/paint, and polymer-based magnetic particle testing.
  • Suitable for raw materials, semi-finished and finished components, and welds of any heat treatment.

• Principles of Magnetic Particle Testing

  • Detects cracks and discontinuities by utilizing magnetic fields to reveal sites of magnetic flux leakage.
  • Discontinuities are indicated by magnetic particles accumulating where flux leaks due to structural anomalies.

• Testing Procedures

  • Describes both continuous and residual magnetization techniques.
  • Emphasizes the importance of proper particle application, field strength, field direction, and surface preparation for optimal results.

• Fluorescent and Nonfluorescent Particles

  • Use of fluorescent particles under UV-A light enhances detection sensitivity, especially for small flaws.
  • Nonfluorescent methods rely on visible contrast and are more suited to field conditions.

• Personnel and Agency Requirements

  • Personnel should be qualified per standards such as ASNT SNT-TC-1A, ANSI/ASNT CP-189, or NAS 410.
  • Testing agencies must comply with ASTM E543 specification standards.

• Limitations

  • The standard serves as a reference for procedure development but does not set part acceptance criteria.
  • Requires separate specification or agreement for defining rejection limits, such as size and orientation of indications.

Applications

Magnetic particle testing according to ASTM E709-21 delivers crucial inspection capabilities for any industry dealing with ferromagnetic materials. Practical applications include:

• Quality Control in Manufacturing

  • Inspecting billets, castings, forgings, bars, plates, and welds for cracks or inclusions during or after production.

• Preventive Maintenance

  • Routine inspection of high-stress components in power plants, transportation, and infrastructure to detect fatigue or service-induced damage before failure occurs.

• Aerospace and Automotive

  • Ensuring structural integrity of safety-critical parts, such as aircraft landing gear, automotive axles, or railway components.

• Field Inspections

  • Portable methods enable examination in difficult-to-access locations, making it valuable for onsite structural assessments and in-situ repair validation.

• Weld Inspection

  • Checking for cracks, porosity, and incomplete fusion in new installations and repairs, supporting quality and safety requirements.

Related Standards

For the best practice in magnetic particle testing, ASTM E709-21 should be used in conjunction with related standards and guidelines, including:

• ASTM E1444/E1444M - Practice for Magnetic Particle Testing
  Provides more detailed procedures for standard magnetic particle testing.
• ASTM E3024/E3024M - Practice for Magnetic Particle Testing for General Industry
• ASTM E543 - Specification for Agencies Performing Nondestructive Testing
• ASNT SNT-TC-1A - Personnel Qualification and Certification in Nondestructive Testing
• ANSI/ASNT CP-189 - Qualification and Certification of Nondestructive Testing Personnel
• NAS 410 - Nondestructive Testing Personnel Qualification and Certification
• AMS 3040-3046 - Aerospace Materials Specifications for different magnetic particle materials

By following ASTM E709-21 and related standards, organizations can ensure safe, repeatable, and reliable detection of surface and near-surface flaws in ferromagnetic materials, supporting compliance, quality assurance, and asset integrity across a range of industrial sectors.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E709 − 21
Standard Guide for
Magnetic Particle Testing
This standard is issued under the fixed designation E709; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* andorientationofindicationsthatareunacceptableinaspecific
part versus those which need not be removed before part
1.1 This guide covers techniques for both dry and wet
acceptance.Conditionswherereworkorrepairisnotpermitted
magnetic particle testing, a nondestructive method for detect-
should be specified.
ing cracks and other discontinuities at or near the surface in
ferromagnetic materials. Magnetic particle testing may be
1.4 This guide describes the use of the following magnetic
applied to raw material, semifinished material (billets, blooms,
particle method techniques.
castings, and forgings), finished material and welds, regardless
1.4.1 Dry magnetic powder (see 8.4),
of heat treatment or lack thereof. It is useful for preventive
1.4.2 Wet magnetic particle (see 8.5),
maintenance testing.
1.4.3 Magnetic slurry/paint magnetic particle (see 8.5.7),
1.1.1 This guide is intended as a reference to aid in the
and
preparation of specifications/standards, procedures and tech-
1.4.4 Polymer magnetic particle (see 8.5.8).
niques.
1.5 Personnel Qualification—Personnel performing exami-
1.2 This guide is also a reference that may be used as
nations in accordance with this guide should be qualified and
follows:
certifiedinaccordancewithASNTRecommendedPracticeNo.
1.2.1 To establish a means by which magnetic particle
SNT-TC-1A, ANSI/ASNT Standard CP-189, NAS410, or as
testing, procedures recommended or required by individual
specified in the contract or purchase order.
organizations, can be reviewed to evaluate their applicability
and completeness.
1.6 Nondestructive Testing Agency—If a nondestructive
1.2.2 To aid in the organization of the facilities and person-
testing agency as described in Specification E543 is used to
nel concerned in magnetic particle testing.
perform the examination, the nondestructive testing agency
1.2.3 To aid in the preparation of procedures dealing with
should meet the requirements of Specification E543.
the examination of materials and parts. This guide describes
1.7 Units—The values stated in inch-pound units are to be
magnetic particle testing techniques that are recommended for
regarded as standard. The values given in parentheses are
a great variety of sizes and shapes of ferromagnetic materials
mathematical conversions to SI units that are provided for
and widely varying examination requirements. Since there are
information only and are not considered standard.
many acceptable differences in both procedure and technique,
the explicit requirements should be covered by a written
1.8 Warning—Mercuryhasbeendesignatedbymanyregu-
procedure (see Section 21).
latory agencies as a hazardous material that can cause serious
medical issues. Mercury, or its vapor, has been demonstrated
1.3 This guide does not indicate, suggest, or specify accep-
to be hazardous to health and corrosive to materials. Caution
tance standards for parts/pieces examined by these techniques.
should be taken when handling mercury and mercury contain-
It should be pointed out, however, that after indications have
ing products. See the applicable product Safety Data Sheet
been produced, they must be interpreted or classified and then
(SDS) for additional information. Users should be aware that
evaluated. For this purpose there should be a separate code,
selling mercury or mercury containing products, or both, into
specification, or a specific agreement to define the type, size,
your state or country may be prohibited by law.
location, degree of alignment and spacing, area concentration,
1.9 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
This guide is under the jurisdiction ofASTM Committee E07 on Nondestruc-
responsibility of the user of this standard to establish appro-
tive Testing and is the direct responsibility of Subcommittee E07.03 on Liquid
priate safety, health, and environmental practices and deter-
Penetrant and Magnetic Particle Methods.
CurrenteditionapprovedJune1,2021.PublishedJuly2021.Originallyapproved mine the applicability of regulatory limitations prior to use.
in 1980. Last previous edition approved in 2015 as E709–15. DOI: 10.1520/
1.10 This international standard was developed in accor-
E0709-21.
dance with internationally recognized principles on standard-
For ASME Boiler and Pressure Vessel Code Applications, see related Guide
SE-709 in Section II of that Code. ization established in the Decision on Principles for the
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E709 − 21
Development of International Standards, Guides and Recom- 2.3 ASNT Documents:
mendations issued by the World Trade Organization Technical SNT-TC-1APersonnel Qualification and Certification in
Barriers to Trade (TBT) Committee. Nondestructive Testing
CP-189ASNT Qualification and Certification of Nonde-
2. Referenced Documents
structive Testing Personnel
2.1 ASTM Standards:
2.4 Federal Standards:
D93Test Methods for Flash Point by Pensky-Martens
A-A-59230Fluid, Magnetic Particle Inspection, Suspension
Closed Cup Tester
FED-STD-313Material Safety Data Sheets Preparation and
D445Test Method for Kinematic Viscosity of Transparent
the Submission of
andOpaqueLiquids(andCalculationofDynamicViscos-
2.5 OSHA Document:
ity)
29 CFR1910.1200 Hazard Communication
E165/E165MPractice for Liquid Penetrant Testing for Gen-
2.6 AIA Documents:
eral Industry
NAS410Nondestructive Testing Personnel Qualification
E543Specification forAgencies Performing Nondestructive
and Certification
Testing
E1316Terminology for Nondestructive Examinations
2.7 ISO Standard:
E1444/E1444MPractice for Magnetic Particle Testing
ISO 7810Identification Cards—Physical Characteristics
E3024/E3024MPractice for Magnetic Particle Testing for
General Industry
3. Terminology
2.2 SAE: Aerospace Materials Specifications:
3.1 For definitions of terms used in the practice, refer to
AMS 2300 Premium Aircraft Quality Steel Cleanliness
Terminology E1316.
Magnetic Particle Inspection Procedure
AMS2301Aircraft Quality Steel Cleanliness Magnetic Par-
4. Summary of Guide
ticle Inspection Procedure
4.1 Principle—The magnetic particle method is based on
AMS2303Aircraft Quality Steel Cleanliness Martensitic
establishing a magnetic field with high flux density in a
Corrosion Resistant Steels Magnetic Particle Inspection
ferromagnetic material. The flux lines must spread out when
Procedure
they pass through non-ferromagnetic material such as air in a
AMS2641Vehicle Magnetic Particle Inspection
discontinuity or an inclusion. Because flux lines can not cross,
AMS 3040 Magnetic Particles, Non-fluorescent, Dry
thisspreadingactionmayforcesomeofthefluxlinesoutofthe
Method
material (flux leakage). Flux leakage is also caused by reduc-
AMS 3041 Magnetic Particles, Non-fluorescent, Wet
tioninferromagneticmaterial(cross-sectionalchange),asharp
Method, Oil Vehicle, Ready to Use
dimensional change, or the end of the part. If the flux leakage
AMS 3042 Magnetic Particles, Non-fluorescent, Wet
is strong enough, fine magnetic particles will be held in place
Method, Dry Powder
and an accumulation of particles will be visible under the
AMS3043MagneticParticles,Non-fluorescent,OilVehicle,
proper lighting conditions. While there are variations in the
Aerosol Packaged
magnetic particle method, they all are dependent on this
AMS3044Magnetic Particles, Fluorescent, Wet Method,
principle, that magnetic particles will be retained at the
Dry Powder
locationsofmagneticfluxleakage.Theamountoffluxleakage
AMS 3045 Magnetic Particles, Non-fluorescent, Wet
at discontinuities depends primarily on the following factors:
Method, Oil Vehicle, Ready to Use
fluxdensityinthematerial,andsize,orientation,andproximity
AMS 3046 Magnetic Particles, Non-fluorescent, Wet
tothesurfaceofadiscontinuity.Withlongitudinalfields,allof
Method, Oil Vehicle, Aerosol Packaged
the flux lines must complete their loops though air and an
AMS5062Steel, Low Carbon Bars, Forgings, Tubing,
excessively strong magnetic field may interfere with examina-
Sheet, Strip, and Plate 0.25 Carbon, Maximum
tion near the flux entry and exit points due to the high
AMS5355Investment Castings
flux-density present at these points.
AMS-I-83387Inspection Process, Magnetic Rubber
AS 4792Water ConditioningAgents forAqueous Magnetic
Particle Inspection
AS5282Tool Steel Ring Standard for Magnetic Particle 5
AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
Inspection 28518, 1711Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
AS5371Reference Standards Notched Shims for Magnetic
Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
Particle Inspection
www.dodssp.daps.mil.
Available from Occupational Safety and Health Administration (OSHA), 200
Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov.
3 8
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available fromAerospace IndustriesAssociation ofAmerica, Inc. (AIA), 1000
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM WilsonBlvd.,Suite1700,Arlington,VA22209-3928,http://www.aia-aerospace.org.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Available from International Organization for Standardization (ISO), ISO
Available from Society of Automotive Engineers (SAE), 400 Commonwealth Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Dr., Warrendale, PA 15096-0001, http://www.sae.org. Switzerland, https://www.iso.org.
E709 − 21
4.2 Method—While this practice permits and describes (see 8.5), magnetic slurries/paints (see 8.5.7), and magnetic
many variables in equipment, materials, and procedures, there polymer dispersions (see 8.5.8).
are three steps essential to the method:
4.5 Evaluation of Indications—When the material to be
4.2.1 The part must be magnetized.
examinedhasbeenproperlymagnetized,themagneticparticles
4.2.2 Magnetic particles of the type designated in the
have been properly applied, and the excess particles properly
contract/purchase order/specification should be applied while
removed, there will be accumulations of magnetic particles
the part is magnetized or immediately thereafter.
remaining at the points of flux leakage. These accumulations
4.2.3 Any accumulation of magnetic particles must be
show the distortion of the magnetic field and are called
observed, interpreted, and evaluated.
indications. Without disturbing the particles, the indications
4.3 Magnetization: must be examined, classified, compared with the acceptance
4.3.1 Ways to Magnetize—A ferromagnetic material can be standards, and a decision made concerning the disposition of
magnetized either by passing an electric current through the the material that contains the indication.
material or by placing the material within a magnetic field
4.6 Typical Magnetic Particle Indications:
originated by an external source. The entire mass or a portion
4.6.1 Surface Discontinuities—Surface discontinuities, with
of the mass can be magnetized as dictated by size and
few exceptions, produce sharp, distinct patterns (see Annex
equipmentcapacityorneed.Aspreviouslynoted,inordertobe
A1).
detectable, the discontinuity must interrupt the normal path of
4.6.2 Near-surface Discontinuities—Near-surface disconti-
the magnetic field lines. If a discontinuity is open to the
nuities produce less distinct indications than those open to the
surface, the flux leakage attracting the particles will be at the
surface. The patterns tend to be broad, rather than sharp, and
maximum value for that particular discontinuity. When that
the particles are less tightly held (see Annex A1).
same discontinuity is below the surface, flux leakage evident
on the surface will be a lesser value. 5. Significance and Use
4.3.2 Field Direction—If a discontinuity is oriented parallel
5.1 The magnetic particle method of nondestructive testing
to the magnetic field lines, it may be essentially undetectable.
indicates the presence of surface and near-surface discontinui-
Therefore,sincediscontinuitiesmayoccurinanyorientation,it
ties in materials that can be magnetized (ferromagnetic). This
may be necessary to magnetize the part or the area of interest
method can be used for production examination of parts/
twice or more sequentially in different directions by the same
components or structures and for field applications where
method or a combination of different methods (see Section 13)
portability of equipment and accessibility to the area to be
to induce magnetic field lines in a suitable direction in which
examined are factors. The ability of the method to find small
to perform an adequate examination.
discontinuities can be enhanced by using fluorescent particles
4.3.3 Field Strength—The magnetic field must be of suffi-
suspended in a suitable vehicle and by introducing a magnetic
cient strength to indicate those discontinuities which are
field of the proper strength whose orientation is as close as
unacceptable, yet must not be so strong that an excess of local
possible to 90° to the direction of the suspected discontinuity
particle accumulation masks relevant indications (see Section
(see 4.3.2). A smoother surface or a pulsed current improves
14).
mobility of the magnetic particles under the influence of the
4.4 Types of Magnetic Particles and Their Use—There are magnetic field to collect on the surface where magnetic flux
various types of magnetic particles available for use in mag-
leakage occurs.
netic particle testing. They are available as dry powders
6. Equipment
(fluorescent and nonfluorescent) ready for use as supplied (see
8.4), powder concentrates (fluorescent and nonfluorescent) for 6.1 Types—There are a number of types of equipment
dispersion in water or suspending in light petroleum distillates availableformagnetizingferromagneticpartsandcomponents.
FIG. 1 (a) Articulating Yoke Method of Part Magnetization
E709 − 21
With the exception of a permanent magnet, all equipment may result in metallurgical damage (softening, hardening,
requires a power source capable of delivering the required cracking, etc.). Open-circuit voltages should not exceed 25 V.
current levels to produce the magnetic field. The current used
6.4.1 Remote Control Switch—A remote-control switch,
dictates the sizes of cables and the capability of relays,
which may be built into the prod handles, should be provided
switching contacts, meters and rectifier if the power source is
to permit the current to be turned on after the prods have been
alternating current.
properly placed and to turn it off before the prods are removed
in order to prevent arcing (arc burns).
6.2 Portability—Portability, which includes the ability to
hand carry the equipment, can be obtained from yokes,
6.5 Bench Unit—Atypical bench type unit is shown in Fig.
portable coils with power supplies, and capacitor discharge
3. The unit normally is furnished with a head/tailstock combi-
power supplies with cables. Generally, portable coils provide
nation along with a fixed coil (see Fig. 4).
high magnetizing forces by using higher numbers of turns to
6.6 UV-A Lamps, which are portable, hand-held, perma-
compensate for their lower current flow. Capacitor discharge
nently mounted or fixed, and used to examine parts, should be
units use high current storage capacity and provide these high
checked for output at the verification intervals specified in
current levels for only a very short duration.
Table 2 and after bulb or filter replacement. A longer period
6.3 Yokes—Yokes are usually C-shaped electromagnets
may be used if a plan justifying this extension is prepared by
whichinduceamagneticfieldbetweenthepoles(legs)andare
theNDTfacilityoritsdelegate.Minimumacceptableintensity
used for local magnetization (Fig. 1(a)). Many portable yokes
is 1000 µW/cm at the examination surface.
have articulated legs (poles) that allow the legs to be adjusted
NOTE 1—When using a mercury vapor style lamp, a change in line
to contact irregular surfaces or two surfaces that join at an
voltage greater than 610% can cause a change in output and consequen-
angle.
tiallossofinspectionperformance.Aconstantvoltagetransformermaybe
6.3.1 Permanent Magnets—Permanent magnets (Fig. 1(b))
used where there is evidence of voltage changes greater than 10 %.
are available but their use may be restricted for many applica-
6.6.1 UV-A lamps that use a UV-A LED source shall
tions.This restriction may be due to application impracticality,
produce a peak wavelength at 360 to 370 nanometers as
or due to the specifications governing the examination. Perma-
measured with a spectroradiaometer. When requested, the
nent magnets can lose their magnetic field generating capacity
manufacturer shall provide a certification thereof.
by being partially demagnetized by a stronger flux field, being
6.6.2 Battery-powered UV-A lamps used to examine parts
damaged, or dropped. In addition, the particle mobility created
shall have their intensity measured prior to use and after each
by AC current or HW current pulsations produced by electro-
use.
magnetic yokes are not present. Particles, steel filings, chips,
and scale clinging to the poles can create a housekeeping
6.7 Equipment Verification—See Section 20.
problem.
7. Examination Area
6.4 Prods—Prodsareusedforlocalmagnetizations,seeFig.
2. The prod tips that contact the piece should be aluminum,
7.1 UV-A Intensity for Examination—Magnetic indications
copper braid, or copper pads rather than solid copper. With
found using nonfluorescent particles are examined under vis-
solid copper tips, accidental arcing during prod placement or
iblelight.Indicationsfoundusingfluorescentparticlesmustbe
removal can cause copper penetration into the surface which
examined under UV-A irradiance. This requires a darkened
area with accompanying control of the visible light intensity.
7.1.1 Visible Light Intensity—The intensity of the visible
light at the surface of the part/work piece undergoing nonfluo-
rescentparticleexaminationisrecommendedtobeaminimum
of 100 foot candles (1076 lux).
7.1.1.1 Field Examinations—For some field examinations
usingnonfluorescentparticles,visiblelightintensitiesaslowas
50 foot candles (538 lux) may be used when agreed on by the
contracting agency.
7.1.1.2 Ambient Visible Light—The intensity of ambient
visible light in the darkened area where fluorescent magnetic
particle testing is performed is recommended to not exceed 2
foot candles (21.5 lux).
7.1.2 UV-A Irradiance:
7.1.2.1 UV-A Intensity—The UV-Airradiance at the exami-
nation surface is recommended to not be less than 1000
µW/cm when measured with a suitable UV-A radiometer.
7.1.2.2 UV-ALampWarm-up—Whenusingamercuryvapor
bulb, allow the UV-Alamp to warm up for a minimum of five
minutes prior to its use or measurement of the intensity of the
FIG. 1 (b) Permanent Magnet Yoke Method of Part Magnetization
(continued) ultraviolet light UV-Aemitted.When using LED UV-Alamps,
E709 − 21
FIG. 2 Prods
prior to examining parts under UV irradiance. (Warning—
Photochromicorpermanentlytintedlensesshouldnotbeworn
during examination.)
7.2 Housekeeping—The examination area should be kept
free of interfering debris. If fluorescent materials are involved,
the area should also be kept free of fluorescent objects not
related to the part/piece being examined.
8. Magnetic Particle Materials
8.1 Magnetic Particle Properties:
8.1.1 Dry Particle Properties—AMS3040 describes the
generally accepted properties of dry method particles.
8.1.2 Wet Particle Properties—The following documents
describe the generally accepted properties of wet method
particles in their various forms:
FIG. 3 Bench Unit
AMS 3041 Magnetic Particles, Non-fluorescent, Wet
Method, Oil Vehicle, Ready to Use
AMS 3042 Magnetic Particles, Non-fluorescent, Wet
it is recommended to allow the lamp to stabilize in accordance
Method, Dry Powder
with the manufacturer’s recommendations prior to use or
AMS 3043 Magnetic Particles, Non-fluorescent, Oil
measurement.
7.1.3 Dark Area Eye Adaptation—The generally accepted Vehicle, Aerosol Packaged
AMS3044 Magnetic Particles, Fluorescent, Wet Method,
practiceisthataninspectorbeinthedarkenedareaatleastone
(1) minute so that his or her eyes will adapt to dark viewing Dry Powder
E709 − 21
FIG. 4 Bench Fixed Coil and Field Distribution
AMS 3045 Magnetic Particles, Non-fluorescent, Wet temperatures this high, making the contrast less effective.
Method, Oil Vehicle, Ready to Use Fluorescent dry particles cannot be used at this high a
AMS 3046 Magnetic Particles, Non-fluorescent, Wet temperature; the manufacturer should be contacted for the
Method, Oil Vehicle, Aerosol Packaged temperature limitations (see 15.1.2).
8.1.3 Suspension Vehicle—The suspension vehicle for wet-
8.4.1 Advantages—The dry magnetic particle technique is
method examination may be either a light oil distillate fluid
generally superior to the wet technique for detection of
(refer to AMS2641 or A-A-52930) or a conditioned water
near-surface discontinuities on parts with a gross indication
vehicle (refer to AS4792).
size. Refer to 8.5.1: (a) for large objects when using portable
equipment for local magnetization; (b) superior particle mo-
8.2 Particle Types—The particles used in either dry or wet
bility is obtained for relatively deep-seated flaws using half-
magneticparticletestingtechniquesarebasicallyfinelydivided
wave rectified current as the magnetizing source; (c) ease of
ferromagnetic materials which have been treated to impart
removal.
color (fluorescent and nonfluorescent) in order to make them
8.4.2 Disadvantages—The dry magnetic particle technique;
highly visible (contrasting) against the background of the
(a) cannot be used in confined areas without proper safety
surface being examined. The particles are designed for use
breathing apparatus; (b) can be difficult to use in overhead
eitherasafreeflowingdrypowderorforsuspensionatagiven
magnetizing positions; (c) does not always leave evidence of
concentration in a suitable liquid medium.
complete coverage of part surface as with the wet technique;
8.3 Particle Characteristics—The magnetic particles must
(d) is likely to have lower production rates than the wet
have high permeability to allow ease of magnetizing and
technique; and (e) is difficult to adapt to any type of automatic
attraction to the site of the flux leakage and low retentivity so
system.
they will not be attracted (magnetic agglomeration) to each
8.4.3 Nonfluorescent Colors—Although dry magnetic par-
other. Control of particle size and shape is required to obtain
ticle powder can be almost any color, the most frequently
consistent results. The particles should be nontoxic, free from
employed colors are light gray, black, red, or yellow. The
rust, grease, paint, dirt, and other deleterious materials that
choice is generally based on maximum contrast with the
might interfere with their use; see 20.5 and 20.6. Both dry and
surface to be examined.The examination is done under visible
wetparticlesareconsideredsafewhenusedinaccordancewith
light.
the manufacturer’s instructions. They generally afford a very
8.4.4 Fluorescent—Fluorescent dry magnetic particles are
low hazard potential with regard to flammability and toxicity.
also available, but are not in general use primarily because of
8.4 Dry Particles—Dry magnetic powders are designed to
their higher cost and use limitations. They require a UV-A
be used as supplied and are applied by spraying or dusting
source and a darkened work area. These requirements are not
directly onto the surface of the part being examined. They are
often available in the field-type locations where dry magnetic
generally used on an expendable basis because of the require-
particle examinations are especially suitable.
ment to maintain particle size and control possible contamina-
8.4.5 Dual Response—Dual response particles are available
tion. Reuse is not a normal practice. Dry powders may also be
that are readily detectable in visible light and also display
used under extreme environmental conditions. They are not
fluorescence when viewed under UV-A or a combination
affected by cold; therefore examination can be carried out at
visible and UV-A. Use in accordance with the manufacturer’s
temperatures that would thicken or freeze wet baths. They are
recommendations.
also heat resistant; some powders may be usable at tempera-
tures up to 600°F (315°C). Some colored, organic coatings 8.5 Wet Particle Systems—Wet magnetic particles are de-
applied to dry particles to improve contrast lose their color at signed to be suspended in a vehicle such as water or light
E709 − 21
petroleum distillate at a given concentration for application to (3) Characteristics—Petroleum distillate vehicles to be
theexaminationsurfacebyflowing,spraying,orpouring.They used in wet magnetic particle testing should possess the
are available in both fluorescent and nonfluorescent concen-
following:(a)viscosityshouldnotexceed3.0cSt(3mm /s)at
trates. In some cases the particles are premixed with the
100°F (38°C) and not more than 5.0 cSt (5 mm /s) at the
suspendingvehiclebythesupplier,butusuallytheparticlesare
lowest temperature at which the vehicle will be used; when
supplied as a dry concentrate or paste concentrate which is
verified in accordance with Test Method D445, in order not to
mixed with the distillate or water by the user.The suspensions
impedeparticlemobility(see20.7.3),(b)minimumflashpoint,
are normally used in wet horizontal magnetic particle equip-
whenverifiedinaccordancewithTestMethodsD93,shouldbe
ment in which the suspension is retained in a reservoir and
200°F (93°C) in order to minimize fire hazards (see 20.7.4),
recirculated for continuous use. The suspension may also be
(c) odorless; not objectionable to user, (d) low inherent
usedonanexpendablebasisdispensedfromanaerosolorother
fluorescenceifusedwithfluorescentparticles;thatis,itshould
suitable dispensers.
not interfere significantly with the fluorescent particle indica-
8.5.1 Primary Use—Because the particles used are smaller,
tions (see 20.6.4.1), and (e) nonreactive; should not degrade
wet method techniques are generally used to locate smaller
suspended particles.
discontinuities than the dry method is used for. The liquid
8.5.4.2 Water Vehicles with Conditioning Agents—Water
vehicles used may not perform satisfactorily when their vis-
maybeusedasasuspensionvehicleforwetmagneticparticles
cosity exceeds 5cSt (5 mm /s) at the operating temperature. If
providedsuitableconditioningagentsareaddedwhichprovide
the suspension vehicle is a hydrocarbon, its flash point limits
proper wet dispersing, in addition to corrosion protection for
the top temperature of usage. Mixing equipment for bulk
reservoirsormanualagitationforportabledispensersisusually thepartsbeingexaminedandtheequipmentinuse.Plainwater
requiredtokeepwetmethodparticlesuniformlyinsuspension. does not disperse some types of magnetic particles, does not
wet all surfaces, and is corrosive to parts and equipment. On
8.5.2 Where Used—The wet fluorescent method usually is
the other hand, conditioned water suspensions of magnetic
performed indoors or in areas where shelter and ambient light
level can be controlled and where proper application equip- particles are safer to use since they are nonflammable. The
ment is available. selectionandconcentrationoftheconditioningagentshouldbe
as recommended by the particle manufacturer. The following
8.5.3 Color—The color chosen for any given examination
shouldbeonethatbestcontrastswiththetestsurface.Because are recommended properties for water vehicles containing
contrast is invariably higher with fluorescent materials, these conditioning agents for use with wet magnetic particle testing:
are utilized in most wet process examinations. Fluorescent wet
(1) Wetting Characteristics—The vehicle should have
method particles normally glow a bright yellow-green when
good wetting characteristics; that is, wet the surface to be
viewed under UV-A irradiance, although other colors are
examined, give even, complete coverage without evidence of
available. Non-fluorescent particles are usually black or red-
dewetting the examination surface. The surface tension (cov-
dish brown, although other colors are available. Dual response
erage) should be observed independently under both UV-A
particlesareavailablethatarereadilydetectableinvisiblelight
irradiance and visible light. Smooth examination surfaces
and also display fluorescence when viewed under UV-A or a
requirethatagreaterpercentageofwettingagentbeaddedthan
combinationvisibleilluminationandUV-Airradiance.Referto
is required for rough surface. Nonionic wetting agents are
8.5.5.
recommended (see 20.7.5).
8.5.4 Suspension Vehicles—Generally the particles are sus-
(2) Suspension Characteristics—Impart good dispersibil-
pended in a light petroleum (low-viscosity) distillate or condi-
ity; that is, thoroughly disperse the magnetic particles without
tionedwater.(Ifsulfurorchlorinelimitsarespecified,useTest
evidence of particle agglomeration.
Methods E165/E165M, Annex A2 or A4 to determine their
(3) Foaming—Minimize foaming; that is, it should not
values.
produce excessive foam which would interfere with indication
8.5.4.1 Petroleum Distillates—Low-viscosity light petro-
formation or cause particles to form scum with the foam.
leumdistillatesvehicles(AMS2641Type1orequal)areideal
(4) Corrosiveness—Itshouldnotcorrodepartstobeexam-
for suspending both fluorescent and nonfluorescent magnetic
ined or the equipment in which it is used.
particles and are commonly employed.
(5) Viscosity Limit—Theviscosityoftheconditionedwater
(1) Advantages—Two significant advantages for the use of
should not exceed a maximum viscosity of 3 cSt (3 mm /s) at
petroleum distillate vehicles are: (a) the magnetic particles are
100°F (38°C) (see 20.7.3).
suspended and dispersed in petroleum distillate vehicles with-
(6) Fluorescence—The conditioned water should not pro-
out the use of conditioning agents; and (b) the petroleum
duceexcessivefluorescenceifintendedforusewithfluorescent
distillate vehicles provide a measure of corrosion protection to
particles.
parts and the equipment used.
(7) Nonreactiveness—The conditioned water should not
(2) Disadvantages—Principal disadvantages are
cause deterioration of the suspended magnetic particles.
flammability, fumes, and availability. It is essential, therefore,
(8) Water pH—ThepHoftheconditionedwatershouldnot
to select and maintain readily available sources of supply of
be less than 7.0 or exceed 10.5.
petroleum distillate vehicles that have as high a flash point as
(9) Odor—The conditioned water should be essentially
practicable to avoid possible flammability problems and pro-
vide a work area with proper ventilation. odorless.
E709 − 21
8.5.5 Concentration of Wet Magnetic Particle Suspension— ties.As with nonconductive coatings, it must be demonstrated
The initial bath concentration of suspended magnetic particles that the unacceptable discontinuities can be detected through
shouldbeasspecifiedorasrecommendedbythemanufacturer the coating.
and should be checked by settling volume measurements and
9.1.3 Residual Magnetic Fields—If the part/piece holds a
maintainedatthespecifiedconcentrationonadailybasis.Ifthe
residualmagneticfieldfromapreviousmagnetizationthatwill
concentration is not maintained properly, examination results
interfere with the examination, the part must be demagnetized.
can vary greatly. The concentration of dual response particles
See Section 18.
in the wet-method bath suspension may be adjusted to best
9.2 Cleaning Examination Surface—Cleaning of the exami-
perform in the desired lighting environment. Higher particle
nation surface may be accomplished by detergents, organic
concentrationisrecommendedforvisiblelightareasandlower
solvents, or mechanical means. As-welded, as-rolled, as-cast,
particle concentration is recommended for UV-Aareas. Use in
or as-forged surfaces are generally satisfactory, but if the
accordancewiththeparticlemanufacturer’srecommendations.
surfaceisunusuallynonuniform,aswithburned-insand,avery
8.5.6 Application of Wet Magnetic Particles (see 15.2).
rough weld deposit, or scale, interpretation may be difficult
8.5.7 Magnetic Slurry/Paint Systems—Another type of ex-
becauseofmechanicalentrapmentofthemagneticparticles.In
amination vehicle is the magnetic slurry/paint type consisting
case of doubt, any questionable area should be recleaned and
of a heavy oil in which flake-like particles are suspended. The
reexamined (see 9.1).
material is normally applied by brush before the part is
9.2.1 Plugging and Masking Small Holes and Openings—
magnetized. Because of the high viscosity, the material does
Unless prohibited by the purchaser, small openings and oil
not rapidly run off surfaces, facilitating the examination of
holesleadingtoobscurepassagesorcavitiescanbepluggedor
vertical or overhead surfaces. The vehicles may be
masked with a suitable nonabrasive material which is readily
combustible, but the fire hazard is very low. Other hazards are
removed. In the case of engine parts, the material must be
very similar to those of the oil and water vehicles previously
soluble in oil. Effective masking must be used to protect
described.
componentsthatmaybedamagedbycontactwiththeparticles
8.5.8 Polymer-Based Systems—The vehicle used in the
or particle suspension.
magneticpolymerisbasicallyaliquidpolymerwhichdisperses
the magnetic particles and which cures to an elastic solid in a
10. Sequence of Operations
given period of time, forming fixed indications. Viscosity
limits of standard wet technique vehicles do not apply. Care
10.1 Sequencing Particle Application and Establishing
should be exercised in handling these polymer materials. Use
Magnetic Flux Field—The sequence of operation in magnetic
in accordance with manufacturer’s instructions and precau-
particle examination applies to the relationship between the
tions. This technique is particularly applicable to examination
timing and application of particles and establishing the mag-
areas of limited visual accessibility, such as bolt holes.
netizing flux field. Two basic techniques apply, that is, con-
tinuous (see 10.1.1 and 10.1.2) and residual (see 10.1.3), both
9. Part Preparation
of which are commonly employed in industry.
9.1 General—The surface of the ferromagnetic part to be 10.1.1 Continuous Magnetization—Continuous magnetiza-
examinedshouldbeessentiallyclean,dry,andfreeofcontami- tion is employed for most applications utilizing either dry or
nants such as dirt, oil, grease, loose rust, loose mill sand, loose wet particles and will provide higher magnetic field strengths,
millscale,lint,thickpaint,weldingflux/slag,andweldsplatter toaidindicationformationbetter,thanresidualmagenticfields.
that might restrict particle movement. See 15.1.2 about apply- The continuous method must be used when performing multi-
ing dry particles to a damp/wet surface. When examining a directional magnetization. The sequence of operation for the
local area, such as a weld, the areas adjacent to the surface to dry and the wet continuous magnetization techniques are
significantly different and are discussed separately in 10.1.1.1
beexamined,asagreedbythecontractingparties,mustalsobe
cleaned to the extent necessary to permit detection of indica- and 10.1.1.2.
tions. See Appendix X6 for more information on steels.
10.1.1.1 Dry Continuous Magnetization Technique—Unlike
9.1.1 Nonconductive Coatings—Thin nonconductive
a wet suspension, dry particles lose most of their mobility
coatings, such as paint in the order of 1 or 2 mil (0.02 to 0.05 when they contact the surface of a part. Therefore, it is
mm) will not normally interfere with the formation of
imperative that the part/area of interest be under the influence
indications, but they must be removed at all points where
of the applied magnetic field while the particles are still
electrical contact is to be made for direct magnetization.
airborne and free to be attracted to leakage fields.This dictates
Indirect magnetization does not require electrical contact with
that the flow of magnetizing current be initiated prior to the
the part/piece. See Section 12.2. If a nonconducting coating/
application of dry magnetic particles and terminated after the
plating is left on the area to be examined that has a thickness
application of powder has been completed and any excess has
greater than 2 mil (0.05 mm), it must be demonstrated that
been blown off. Magnetizing with HW current andAC current
unacceptablediscontinuitiescanbedetectedthroughthemaxi-
provide additional particle mobility on the surface of the part.
mum thickness applied.
Examination with dry particles is usually carried out in
9.1.2 Conductive Coatings—A conductive coating (such as conjunction with prod-type or yoke localized magnetizations,
chrome plating and heavy mill scale on wrought products andbuildupofindicationsisobservedastheparticlesarebeing
resulting from hot forming operations) can mask discontinui- applied.
E709 − 21
10.1.1.2 Wet Continuous Magnetization Technique—The which should be used when near-surface or inside surface
wet continuous magnetization technique involves bathing the discontinuities are of concern.
part with the examination medium to provide an abundant 11.1.2 Half-Wave Rectified Current (HW)—Half-wave cur-
source of suspended particles on the surface of the part and rent is frequently used in conjunction with wet and dry
terminating the bath application immediately prior to the particles because the current pulses provide more mobility to
termination of the magnetizing current. The duration of the the particles.This waveform is used with prods, yokes, mobile
magnetizing current is typically on the order of 0.5 second for and bench units. Half-wave rectified current is used to achieve
eachmagnetizingpulse(shot),withtwoormoreshotsgivento depth of penetration for detection of typical discontinuities
the part. To ensure that indications are not washed away, the foundinweldments,forgings,andferrouscastings.AswithAC
subsequent shots should follow the first while the particles are for magnetization, single-phase current is utilized and the
still mobile on the surface of the part. average value measured as “magnetizing current.”
11.1.3 Full-Wave Rectified Current (FW)—Full-wave cur-
10.1.1.3 Polymer or Slurry Continuous Magnetization
rent may utilize single- or three-phase current. Three-phase
Technique—Prolonged or repeated periods of magnetization
current has the advantage of lower line amperage draws,
are often necessary for polymer- or slurry-base suspensions
whereas single-phase equipment is less expensive. Full-wave
because of slower inherent magnetic particle mobility in the
rectifiedcurrentiscommonlyusedwhentheresidualmethodis
high-viscosity suspension vehicles.
to be employed. Because particle movement, either dry or wet
10.1.2 True Continuous Magnetization Technique—In this
is noticeably less, precautions must be taken to ensure that
technique, the magnetizing current is sustained throughout
sufficient time is allowed for formation of indications.
both the processing and examination of the part.
11.1.4 Direct Current (DC)—Abank of batteries, full-wave
10.1.3 Residual Magnetization Techniques:
rectified AC filtered through capacitors or a DC generator
10.1.3.1 Residual Magnetization—In this technique, the ex-
produce direct magnetizing current. They have largely given
amination medium is applied after the magnetizing force has
way to half-wave rectified or full-wave rectified DC except for
been discontinued. It can be used only if the material being
a few specialized applications, primarily because of broad
examinedhasrelativelyhighretentivitysotheresidualleakage
application advantages when using other types of equipment.
field will be of sufficient strength to attract and hold the
11.1.5 Capacitor Discharge (CD) Current—A bank of ca-
particles and produce indications. This technique may be
pacitorsareusedtostoreenergyandwhentriggeredtheenergy
advantageous for integration with production or handling
reaches high amperage with a very short duration (normally
requirements or when higher than residual field strengths are
less than 25 milliseconds). Because of the short pulse duration
not required to achieve satisfactory results. When inducing
thecurrentrequirementsareaffectedbytheamountofmaterial
circular fields and longitudinal fields of long pieces, residual
to be magnetized as well as the applied amperage. The
fieldsarenormallysufficienttomeetmagnetizingrequirements
capacitor discharge technique is widely used to establish a
consistent with the requirements of Section 14. The residual
residual magnetic field in tubing, casing, line pipe, and drill
method has found wide use examining pipe and tubular goods.
pipe. For specific requirements, see Appendix X8.
For magnetization requirements of oilfield tubulars, refer to
12. Part Magnetization Techniques
Appendix X8. Unless demonstrations with typical parts indi-
cate that the residual field has sufficient strength to produce
12.1 Examination Coverage—All examinations should be
relevantindicationsofdiscontinuities(see20.8)whenthefield
conducted with sufficient area overlap to assure the required
isinproperorientation,thecontinuousmethodshouldbeused.
coverage at the specified sensitivity has been obtained.
12.2 Direct and Indirect Magnetization—A part can be
11. Types of Magnetizing Currents
magnetized either directly or indirectly. For direct magnetiza-
tion the magnetizing current is passed directly through the part
11.1 Basic Current Types—The four basic types of current
creatingamagneticfieldoriented90degreestocurrentflowin
usedinmagneticparticletestingtoestablishpartmagnetization
the part. With indirect magnetization techniques a magnetic
are alternating current (AC), half-wave rectified current (HW),
fieldisinducedinthepart,whichcancreateacircular/toroidal,
full-wave rectified current (FW), and for a special application,
longitudinal, or multidirectional magnetic field in the part.The
DC.
techniques described in 20.8 for verifying that the magnetic
11.1.1 Alternating Current (AC)—Part magnetization with
fields have the anticipated direction and strength should be
alternating current is preferred for those applications where
employed.This is especially important when using multidirec-
examination requirements call for the detection of
tional techniques to examine complex shapes.
discontinuities, such as fatigue cracks, that are open to the
surface to which the magnetizing force is applied. Associated 12.3 Choosing Magnetization Technique—The choice of
withACisa“skineffect”thatconfinesthemagneticfieldator direct or indirect magnetization will depend on such factors as
near to the surface of a part. In contrast, both HW current and size,configuration,oreaseofprocessing.Table1comparesthe
FW current produce a magnetic field having penetrating advantages and limitations of the various methods of part
capabilities proportional to the amount of applied current, magnetization.
E709 − 21
TABLE 1 Advantages and Limitations of the Various Ways of Magnetizing a Part
Magnetizing Technique and Material Form Advantages Limitations
I. Direct Contact Part Magnetization (see 12.3.1)
Head/Tailstock Contact
Solid, relatively small parts (castings, 1. Fast, easy technique. 1. Possibility of arc burns if poor contact conditions
forgings, machined pieces) that can be exist.
processed on a horizontal wet unit
2. Circular magnetic field surrounds current path. 2. Long parts should be examined
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E709 − 15 E709 − 21
Standard Guide for
Magnetic Particle Testing
This standard is issued under the fixed designation E709; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This guide covers techniques for both dry and wet magnetic particle testing, a nondestructive method for detecting cracks and
other discontinuities at or near the surface in ferromagnetic materials. Magnetic particle testing may be applied to raw material,
semifinished material (billets, blooms, castings, and forgings), finished material and welds, regardless of heat treatment or lack
thereof. It is useful for preventive maintenance testing.
1.1.1 This guide is intended as a reference to aid in the preparation of specifications/standards, procedures and techniques.
1.2 This guide is also a reference that may be used as follows:
1.2.1 To establish a means by which magnetic particle testing, procedures recommended or required by individual organizations,
can be reviewed to evaluate their applicability and completeness.
1.2.2 To aid in the organization of the facilities and personnel concerned in magnetic particle testing.
1.2.3 To aid in the preparation of procedures dealing with the examination of materials and parts. This guide describes magnetic
particle testing techniques that are recommended for a great variety of sizes and shapes of ferromagnetic materials and widely
varying examination requirements. Since there are many acceptable differences in both procedure and technique, the explicit
requirements should be covered by a written procedure (see Section 21).
1.3 This guide does not indicate, suggest, or specify acceptance standards for parts/pieces examined by these techniques. It should
be pointed out, however, that after indications have been produced, they must be interpreted or classified and then evaluated. For
this purpose there should be a separate code, specification, or a specific agreement to define the type, size, location, degree of
alignment and spacing, area concentration, and orientation of indications that are unacceptable in a specific part versus those which
need not be removed before part acceptance. Conditions where rework or repair is not permitted should be specified.
1.4 This guide describes the use of the following magnetic particle method techniques.
1.4.1 Dry magnetic powder (see 8.4),
1.4.2 Wet magnetic particle (see 8.5),
1.4.3 Magnetic slurry/paint magnetic particle (see 8.5.7), and
This guide is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.03 on Liquid Penetrant
and Magnetic Particle Methods.
Current edition approved June 1, 2015June 1, 2021. Published June 2015July 2021. Originally approved in 1980. Last previous edition approved in 20142015 as
E709 - 14.E709 – 15. DOI: 10.1520/E0709-15.10.1520/E0709-21.
For ASME Boiler and Pressure Vessel Code Applications, see related Guide SE-709 in Section II of that Code.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E709 − 21
1.4.4 Polymer magnetic particle (see 8.5.8).
1.5 Personnel Qualification—Personnel performing examinations in accordance with this guide should be qualified and certified
in accordance with ASNT Recommended Practice No. SNT-TC-1A, ANSI/ASNT Standard CP-189, NAS 410, or as specified in
the contract or purchase order.
1.6 Nondestructive Testing Agency—If a nondestructive testing agency as described in PracticeSpecification E543 is used to
perform the examination, the nondestructive testing agency should meet the requirements of PracticeSpecification E543.
1.7 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.8 Warning: Warning—Mercury has been designated by many regulatory agencies as a hazardous material that can cause serious
medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Caution should
be taken when handling mercury and mercury containing products. See the applicable product Safety Data Sheet (SDS) for
additional information. Users should be aware that selling mercury or mercury containing products, or both, into your state or
country may be prohibited by law. Mercury has been designated by many regulatory agencies as a hazardous material that can
cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to
materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Safety
Data Sheet (SDS) for additional information. Users should be aware that selling mercury and/or mercury containing products into
your state or country may be prohibited by law.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D93 Test Methods for Flash Point by Pensky-Martens Closed Cup Tester
D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
E165/E165M Practice for Liquid Penetrant Testing for General Industry
E543 Specification for Agencies Performing Nondestructive Testing
E1316 Terminology for Nondestructive Examinations
E1444/E1444M Practice for Magnetic Particle Testing
E3024/E3024M Practice for Magnetic Particle Testing for General Industry
2.2 Society of Automotive Engineers (SAE): SAE: Aerospace Materials Specifications:
AMS 2300 Premium Aircraft Quality Steel Cleanliness Magnetic Particle Inspection Procedure
AMS 2301 Aircraft Quality Steel Cleanliness Magnetic Particle Inspection Procedure
AMS 2303 Aircraft Quality Steel Cleanliness Martensitic Corrosion Resistant Steels Magnetic Particle Inspection Procedure
AMS 2641 Vehicle Magnetic Particle Inspection
AMS 3040 Magnetic Particles, Non-fluorescent, Dry Method
AMS 3041 Magnetic Particles, Non-fluorescent, Wet Method, Oil Vehicle, Ready to Use
AMS 3042 Magnetic Particles, Non-fluorescent, Wet Method, Dry Powder
AMS 3043 Magnetic Particles, Non-fluorescent, Oil Vehicle, Aerosol Packaged
AMS 3044 Magnetic Particles, Fluorescent, Wet Method, Dry Powder
AMS 3045 Magnetic Particles, Non-fluorescent, Wet Method, Oil Vehicle, Ready to Use
AMS 3046 Magnetic Particles, Non-fluorescent, Wet Method, Oil Vehicle, Aerosol Packaged
AMS 5062 Steel, Low Carbon Bars, Forgings, Tubing, Sheet, Strip, and Plate 0.25 Carbon, Maximum
AMS 5355 Investment Castings
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from Society of Automotive Engineers (SAE), 400 Commonwealth Dr., Warrendale, PA 15096-0001, http://www.sae.org.
E709 − 21
AMS-I-83387 Inspection Process, Magnetic Rubber
AS 4792 Water Conditioning Agents for Aqueous Magnetic Particle Inspection
AS 5282 Tool Steel Ring Standard for Magnetic Particle Inspection
AS 5371 Reference Standards Notched Shims for Magnetic Particle Inspection
2.3 American Society for Nondestructive Testing:ASNT Documents:
SNT-TC-1A Personnel Qualification and Certification in Nondestructive Testing
CP-189 ASNT Qualification and Certification of Nondestructive Testing Personnel
2.4 Federal Standards:
A-A-59230 Fluid, Magnetic Particle Inspection, Suspension
FED-STD 313FED-STD-313 Material Safety Data Sheets Preparation and the Submission of
2.5 OSHA Document:
29CFR29 CFR 1910.1200 Hazard Communication
2.6 AIA Documents:
NAS 410 Nondestructive Testing Personnel Qualification and Certification
2.7 ISO Standard:
ISO 7810 Identification Cards—Physical Characteristics
3. Terminology
3.1 For definitions of terms used in the practice, refer to Terminology E1316.
4. Summary of Guide
4.1 Principle—The magnetic particle method is based on establishing a magnetic field with high flux density in a ferromagnetic
material. The flux lines must spread out when they pass through non-ferromagnetic material such as air in a discontinuity or an
inclusion. Because flux lines can not cross, this spreading action may force some of the flux lines out of the material (flux leakage).
Flux leakage is also caused by reduction in ferromagnetic material (cross-sectional change), a sharp dimensional change, or the
end of the part. If the flux leakage is strong enough, fine magnetic particles will be held in place and an accumulation of particles
will be visible under the proper lighting conditions. While there are variations in the magnetic particle method, they all are
dependent on this principle, that magnetic particles will be retained at the locations of magnetic flux leakage. The amount of flux
leakage at discontinuities depends primarily on the following factors: flux density in the material, and size, orientation, and
proximity to the surface of a discontinuity. With longitudinal fields, all of the flux lines must complete their loops though air and
an excessively strong magnetic field may interfere with examination near the flux entry and exit points due to the high flux-density
present at these points.
4.2 Method—While this practice permits and describes many variables in equipment, materials, and procedures, there are three
steps essential to the method:
4.2.1 The part must be magnetized.
4.2.2 Magnetic particles of the type designated in the contract/purchase order/specification should be applied while the part is
magnetized or immediately thereafter.
4.2.3 Any accumulation of magnetic particles must be observed, interpreted, and evaluated.
4.3 Magnetization:
4.3.1 Ways to Magnetize—A ferromagnetic material can be magnetized either by passing an electric current through the material
or by placing the material within a magnetic field originated by an external source. The entire mass or a portion of the mass can
be magnetized as dictated by size and equipment capacity or need. As previously noted, in order to be detectable, the discontinuity
must interrupt the normal path of the magnetic field lines. If a discontinuity is open to the surface, the flux leakage attracting the
Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://www.dodssp.daps.mil.
Available from Occupational Safety and Health Administration (OSHA), 200 Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov.
Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http://www.aia-aerospace.org.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland,
https://www.iso.org.
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particles will be at the maximum value for that particular discontinuity. When that same discontinuity is below the surface, flux
leakage evident on the surface will be a lesser value.
4.3.2 Field Direction—If a discontinuity is oriented parallel to the magnetic field lines, it may be essentially undetectable.
Therefore, since discontinuities may occur in any orientation, it may be necessary to magnetize the part or the area of interest twice
or more sequentially in different directions by the same method or a combination of different methods (see Section 13) to induce
magnetic field lines in a suitable direction in which to perform an adequate examination.
4.3.3 Field Strength—The magnetic field must be of sufficient strength to indicate those discontinuities which are unacceptable,
yet must not be so strong that an excess of local particle accumulation masks relevant indications (see Section 14).
4.4 Types of Magnetic Particles and Their Use—There are various types of magnetic particles available for use in magnetic
particle testing. They are available as dry powders (fluorescent and nonfluorescent) ready for use as supplied (see 8.4), powder
concentrates (fluorescent and nonfluorescent) for dispersion in water or suspending in light petroleum distillates (see 8.5), magnetic
slurries/paints (see 8.5.7), and magnetic polymer dispersions (see 8.5.8).
4.5 Evaluation of Indications—When the material to be examined has been properly magnetized, the magnetic particles have been
properly applied, and the excess particles properly removed, there will be accumulations of magnetic particles remaining at the
points of flux leakage. These accumulations show the distortion of the magnetic field and are called indications. Without disturbing
the particles, the indications must be examined, classified, compared with the acceptance standards, and a decision made
concerning the disposition of the material that contains the indication.
4.6 Typical Magnetic Particle Indications:
4.6.1 Surface Discontinuities—Surface discontinuities, with few exceptions, produce sharp, distinct patterns (see Annex A1).
4.6.2 Near-surface Discontinuities—Near-surface discontinuities produce less distinct indications than those open to the surface.
The patterns tend to be broad, rather than sharp, and the particles are less tightly held (see Annex A1).
5. Significance and Use
5.1 The magnetic particle method of nondestructive testing indicates the presence of surface and near-surface discontinuities in
materials that can be magnetized (ferromagnetic). This method can be used for production examination of parts/components or
structures and for field applications where portability of equipment and accessibility to the area to be examined are factors. The
ability of the method to find small discontinuities can be enhanced by using fluorescent particles suspended in a suitable vehicle
and by introducing a magnetic field of the proper strength whose orientation is as close as possible to 90° to the direction of the
suspected discontinuity (see 4.3.2). A smoother surface or a pulsed current improves mobility of the magnetic particles under the
influence of the magnetic field to collect on the surface where magnetic flux leakage occurs.
FIG. 1 (a) Articulating Yoke Method of Part Magnetization
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6. Equipment
6.1 Types—There are a number of types of equipment available for magnetizing ferromagnetic parts and components. With the
exception of a permanent magnet, all equipment requires a power source capable of delivering the required current levels to
produce the magnetic field. The current used dictates the sizes of cables and the capability of relays, switching contacts, meters
and rectifier if the power source is alternating current.
6.2 Portability—Portability, which includes the ability to hand carry the equipment, can be obtained from yokes, portable coils
with power supplies, and capacitor discharge power supplies with cables. Generally, portable coils provide high magnetizing forces
by using higher numbers of turns to compensate for their lower current flow. Capacitor discharge units use high current storage
capacity and provide these high current levels for only a very short duration.
6.3 Yokes—Yokes are usually C-shaped electromagnets which induce a magnetic field between the poles (legs) and are used for
local magnetization (Fig. 1).(a)). Many portable yokes have articulated legs (poles) that allow the legs to be adjusted to contact
irregular surfaces or two surfaces that join at an angle.
6.3.1 Permanent Magnets—Permanent magnets (Fig. 1(b)) are available but their use may be restricted for many applications. This
restriction may be due to application impracticality, or due to the specifications governing the examination. Permanent magnets
can lose their magnetic field generating capacity by being partially demagnetized by a stronger flux field, being damaged, or
dropped. In addition, the particle mobility created by AC current or HW current pulsations produced by electromagnetic yokes are
not present. Particles, steel filings, chips, and scale clinging to the poles can create a housekeeping problem.
6.4 Prods—Prods are used for local magnetizations, see Fig. 2. The prod tips that contact the piece should be aluminum, copper
braid, or copper pads rather than solid copper. With solid copper tips, accidental arcing during prod placement or removal can cause
copper penetration into the surface which may result in metallurgical damage (softening, hardening, cracking, etc.). Open-circuit
voltages should not exceed 25 V.
6.4.1 Remote Control Switch—A remote-control switch, which may be built into the prod handles, should be provided to permit
the current to be turned on after the prods have been properly placed and to turn it off before the prods are removed in order to
prevent arcing (arc burns).
6.5 Bench Unit—A typical bench type unit is shown in Fig. 3. The unit normally is furnished with a head/tailstock combination
along with a fixed coil (see Fig. 4).
6.6 UV-A Lights (Black Light)—Lamps, which are portable, hand-held, permanently mounted or fixed, and used to examine parts,
should be checked for output at the frequency verification intervals specified in Table 2 and after bulb or filter replacement. A
FIG. 1 (b) Permanent Magnet Yoke Method of Part Magnetization (continued)
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FIG. 2 Prods
FIG. 3 Bench Unit
longer period may be used if a plan justifying this extension is prepared by the NDT facility or its delegate. Minimum acceptable
intensity is 1000 μW/cm at the examination surface.
NOTE 1—When using a mercury vapor style lamp, a change in line voltage greater than 610 % can cause a change in light output and consequential loss
of inspection performance. A constant voltage transformer may be used where there is evidence of voltage changes greater than 10 %.
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FIG. 4 Bench Fixed Coil and Field Distribution
NOTE 2—Some UV-A sources other than mercury vapor, for example, micro-discharge, LED, etc., have been shown to have emission characteristics such
as excessive visible light and UV intensity that may result in fluorescent fade, veiling glare, etc., all of which can significantly degrade examination
reliability.
6.6.1 UV-A lightslamps that use a UV-A LED source shall produce a peak wavelength at 365360 to 370 nanometers as measured
with a spectroradiaometer. When requested, the manufacturer shall provide a certification thereof.
6.6.2 Battery-powered UV-A lightslamps used to examine parts shall have their intensity measured prior to use and after each use.
6.7 Equipment Verification—See Section 20.
7. Examination Area
7.1 LightUV-A Intensity for Examination—Magnetic indications found using nonfluorescent particles are examined under visible
light. Indications found using fluorescent particles must be examined under UV-A (black) light. irradiance. This requires a darkened
area with accompanying control of the visible light intensity.
7.1.1 Visible Light Intensity—The intensity of the visible light at the surface of the part/work piece undergoing nonfluorescent
particle examination is recommended to be a minimum of 100 foot candles (1076 lux).
7.1.1.1 Field Examinations—For some field examinations using nonfluorescent particles, visible light intensities as low as 50 foot
candles (538 lux) may be used when agreed on by the contracting agency.
7.1.1.2 Ambient Visible Light—The intensity of ambient visible light in the darkened area where fluorescent magnetic particle
testing is performed is recommended to not exceed 2 foot candles (21.5 lux).
7.1.2 UV-A (Black) Light: Irradiance:
7.1.2.1 UV-A (Black Light) Intensity—The UV-A irradiance at the examination surface is recommended to not be less than 1000
μW/cm when measured with a suitable UV-A radiometer.
7.1.2.2 UV-A (Black Light) Lamp Warm-up—When using a mercury vapor bulb, allow the UV-A (black) light lamp to warm up
for a minimum of five minutes prior to its use or measurement of the intensity of the ultraviolet light emitted.UV-A emitted. When
using LED UV-A lamps, it is recommended to allow the lamp to stabilize in accordance with the manufacturer’s recommendations
prior to use or measurement.
7.1.3 Dark Area Eye Adaptation—The generally accepted practice is that an inspector be in the darkened area at least one (1)
minute so that his or her eyes will adapt to dark viewing prior to examining parts under UV illumination.irradiance.
(Warning—Photochromic or permanently tinted lenses should not be worn during examination.)
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7.2 Housekeeping—The examination area should be kept free of interfering debris. If fluorescent materials are involved, the area
should also be kept free of fluorescent objects not related to the part/piece being examined.
8. Magnetic Particle Materials
8.1 Magnetic Particle Properties:
8.1.1 Dry Particle Properties—AMS 3040 describes the generally accepted properties of dry method particles.
8.1.2 Wet Particle Properties—The following documents describe the generally accepted properties of wet method particles in
their various forms:
AMS 3041 Magnetic Particles, Non-fluorescent, Wet Method, Oil Vehicle, Ready to Use
AMS 3042 Magnetic Particles, Non-fluorescent, Wet Method, Dry Powder
AMS 3043 Magnetic Particles, Non-fluorescent, Oil Vehicle, Aerosol Packaged
AMS 3044 Magnetic Particles, Fluorescent, Wet Method, Dry Powder
AMS 3045 Magnetic Particles, Non-fluorescent, Wet Method, Oil Vehicle, Ready to Use
AMS 3046 Magnetic Particles, Non-fluorescent, Wet Method, Oil Vehicle, Aerosol Packaged
8.1.3 Suspension Vehicle—The suspension vehicle for wet-method examination may be either a light oil distillate fluid (refer to
AMS 2641 or A-A-52930) or a conditioned water vehicle (refer to AS 4792).
8.2 Particle Types—The particles used in either dry or wet magnetic particle testing techniques are basically finely divided
ferromagnetic materials which have been treated to impart color (fluorescent and nonfluorescent) in order to make them highly
visible (contrasting) against the background of the surface being examined. The particles are designed for use either as a free
flowing dry powder or for suspension at a given concentration in a suitable liquid medium.
8.3 Particle Characteristics—The magnetic particles must have high permeability to allow ease of magnetizing and attraction to
the site of the flux leakage and low retentivity so they will not be attracted (magnetic agglomeration) to each other. Control of
particle size and shape is required to obtain consistent results. The particles should be nontoxic, free from rust, grease, paint, dirt,
and other deleterious materials that might interfere with their use; see 20.5 and 20.6. Both dry and wet particles are considered
safe when used in accordance with the manufacturer’s instructions. They generally afford a very low hazard potential with regard
to flammability and toxicity.
8.4 Dry Particles—Dry magnetic powders are designed to be used as supplied and are applied by spraying or dusting directly onto
the surface of the part being examined. They are generally used on an expendable basis because of the requirement to maintain
particle size and control possible contamination. Reuse is not a normal practice. Dry powders may also be used under extreme
environmental conditions. They are not affected by cold; therefore examination can be carried out at temperatures that would
thicken or freeze wet baths. They are also heat resistant; some powders may be usable at temperatures up to 600°F (315°C).600 °F
(315 °C). Some colored, organic coatings applied to dry particles to improve contrast lose their color at temperatures this high,
making the contrast less effective. Fluorescent dry particles cannot be used at this high a temperature; the manufacturer should be
contacted for the temperature limitations (see 15.1.2).
8.4.1 Advantages—The dry magnetic particle technique is generally superior to the wet technique for detection of near-surface
discontinuities on parts with a gross indication size. Refer to 8.5.1: (a) for large objects when using portable equipment for local
magnetization; (b) superior particle mobility is obtained for relatively deep-seated flaws using half-wave rectified current as the
magnetizing source; (c) ease of removal.
8.4.2 Disadvantages—The dry magnetic particle technique; (a) cannot be used in confined areas without proper safety breathing
apparatus; (b) can be difficult to use in overhead magnetizing positions; (c) does not always leave evidence of complete coverage
of part surface as with the wet technique; (d) is likely to have lower production rates than the wet technique; and (e) is difficult
to adapt to any type of automatic system.
8.4.3 Nonfluorescent Colors—Although dry magnetic particle powder can be almost any color, the most frequently employed
colors are light gray, black, red, or yellow. The choice is generally based on maximum contrast with the surface to be examined.
The examination is done under visible light.
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8.4.4 Fluorescent—Fluorescent dry magnetic particles are also available, but are not in general use primarily because of their
higher cost and use limitations. They require a UV-A (black) light source and a darkened work area. These requirements are not
often available in the field-type locations where dry magnetic particle examinations are especially suitable.
8.4.5 Dual Response—Dual response particles are available that are readily detectable in visible light and also display fluorescence
when viewed under UV-A or a combination visible and UV-A. Use in accordance with the manufacturer’s recommendations.
8.5 Wet Particle Systems—Wet magnetic particles are designed to be suspended in a vehicle such as water or light petroleum
distillate at a given concentration for application to the examination surface by flowing, spraying, or pouring. They are available
in both fluorescent and nonfluorescent concentrates. In some cases the particles are premixed with the suspending vehicle by the
supplier, but usually the particles are supplied as a dry concentrate or paste concentrate which is mixed with the distillate or water
by the user. The suspensions are normally used in wet horizontal magnetic particle equipment in which the suspension is retained
in a reservoir and recirculated for continuous use. The suspension may also be used on an expendable basis dispensed from an
aerosol or other suitable dispensers.
8.5.1 Primary Use—Because the particles used are smaller, wet method techniques are generally used to locate smaller
discontinuities than the dry method is used for. The liquid vehicles used may not perform satisfactorily when their viscosity
exceeds 5cSt (5 mm /s) at the operating temperature. If the suspension vehicle is a hydrocarbon, its flash point limits the top
temperature of usage. Mixing equipment for bulk reservoirs or manual agitation for portable dispensers is usually required to keep
wet method particles uniformly in suspension.
8.5.2 Where Used—The wet fluorescent method usually is performed indoors or in areas where shelter and ambient light level can
be controlled and where proper application equipment is available.
8.5.3 Color—The color chosen for any given examination should be one that best contrasts with the test surface. Because contrast
is invariably higher with fluorescent materials, these are utilized in most wet process examinations. Fluorescent wet method
particles normally glow a bright yellow-green when viewed under UV-A (black) light, irradiance, although other colors are
available. Non-fluorescent particles are usually black or reddish brown, although other colors are available. Dual response particles
are available that are readily detectable in visible light and also display fluorescence when viewed under UV-A light or a
combination visible illumination and UV-A light.irradiance. Refer to 8.5.5.
8.5.4 Suspension Vehicles—Generally the particles are suspended in a light petroleum (low-viscosity) distillate or conditioned
water. (If sulfur or chlorine limits are specified, use Test Methods E165/E165M, Annex A2 or A4 to determine their values.
8.5.4.1 Petroleum Distillates—Low-viscosity light petroleum distillates vehicles (AMS 2641 Type 1 or equal) are ideal for
suspending both fluorescent and nonfluorescent magnetic particles and are commonly employed.
(1) Advantages—Two significant advantages for the use of petroleum distillate vehicles are: (a) the magnetic particles are
suspended and dispersed in petroleum distillate vehicles without the use of conditioning agents; and (b) the petroleum distillate
vehicles provide a measure of corrosion protection to parts and the equipment used.
(2) Disadvantages—Principal disadvantages are flammability, fumes, and availability. It is essential, therefore, to select and
maintain readily available sources of supply of petroleum distillate vehicles that have as high a flash point as practicable to avoid
possible flammability problems and provide a work area with proper ventilation.
(3) Characteristics—Petroleum distillate vehicles to be used in wet magnetic particle testing should possess the following: (a)
2 2
viscosity should not exceed 3.0 cSt (3 mm /s) at 100°F (38°C)100 °F (38 °C) and not more than 5.0 cSt (5 mm /s) at the lowest
temperature at which the vehicle will be used; when verified in accordance with Test Method D445, in order not to impede particle
mobility (see 20.7.3), (b) minimum flash point, when verified in accordance with Test Methods D93, should be 200°F (93°C)200 °F
(93 °C) in order to minimize fire hazards (see 20.7.4), (c) odorless; not objectionable to user, (d) low inherent fluorescence if used
with fluorescent particles; that is, it should not interfere significantly with the fluorescent particle indications (see 20.6.4.1), and
(e) nonreactive; should not degrade suspended particles.
8.5.4.2 Water Vehicles with Conditioning Agents—Water may be used as a suspension vehicle for wet magnetic particles provided
suitable conditioning agents are added which provide proper wet dispersing, in addition to corrosion protection for the parts being
examined and the equipment in use. Plain water does not disperse some types of magnetic particles, does not wet all surfaces, and
is corrosive to parts and equipment. On the other hand, conditioned water suspensions of magnetic particles are safer to use since
they are nonflammable. The selection and concentration of the conditioning agent should be as recommended by the particle
manufacturer. The following are recommended properties for water vehicles containing conditioning agents for use with wet
magnetic particle testing:
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(1) Wetting Characteristics—The vehicle should have good wetting characteristics; that is, wet the surface to be examined,
give even, complete coverage without evidence of dewetting the examination surface. The surface tension (coverage) should be
observed independently under both UV-A (black) light irradiance and visible light. Smooth examination surfaces require that a
greater percentage of wetting agent be added than is required for rough surface. Nonionic wetting agents are recommended (see
20.7.5).
(2) Suspension Characteristics—Impart good dispersability;dispersibility; that is, thoroughly disperse the magnetic particles
without evidence of particle agglomeration.
(3) Foaming—Minimize foaming; that is, it should not produce excessive foam which would interfere with indication
formation or cause particles to form scum with the foam.
(4) Corrosiveness—It should not corrode parts to be examined or the equipment in which it is used.
(5) Viscosity Limit—The viscosity of the conditioned water should not exceed a maximum viscosity of 3 cSt (3 mm /s) at
100°F (38°C)100 °F (38 °C) (see 20.7.3).
(6) Fluorescence—The conditioned water should not produce excessive fluorescence if intended for use with fluorescent
particles.
(7) Nonreactiveness—The conditioned water should not cause deterioration of the suspended magnetic particles.
(8) Water pH—The pH of the conditioned water should not be less than 7.0 or exceed 10.5.
(9) Odor—The conditioned water should be essentially odorless.
8.5.5 Concentration of Wet Magnetic Particle Suspension—The initial bath concentration of suspended magnetic particles should
be as specified or as recommended by the manufacturer and should be checked by settling volume measurements and maintained
at the specified concentration on a daily basis. If the concentration is not maintained properly, examination results can vary greatly.
The concentration of dual response particles in the wet-method bath suspension may be adjusted to best perform in the desired
lighting environment. Higher particle concentration is recommended for visible light areas and lower particle concentration is
recommended for UV-A areas. Use in accordance with the particle manufacturer’s recommendations.
8.5.6 Application of Wet Magnetic Particles (see 15.2).
8.5.7 Magnetic Slurry/Paint Systems—Another type of examination vehicle is the magnetic slurry/paint type consisting of a heavy
oil in which flake-like particles are suspended. The material is normally applied by brush before the part is magnetized. Because
of the high viscosity, the material does not rapidly run off surfaces, facilitating the examination of vertical or overhead surfaces.
The vehicles may be combustible, but the fire hazard is very low. Other hazards are very similar to those of the oil and water
vehicles previously described.
8.5.8 Polymer-Based Systems—The vehicle used in the magnetic polymer is basically a liquid polymer which disperses the
magnetic particles and which cures to an elastic solid in a given period of time, forming fixed indications. Viscosity limits of
standard wet technique vehicles do not apply. Care should be exercised in handling these polymer materials. Use in accordance
with manufacturer’s instructions and precautions. This technique is particularly applicable to examination areas of limited visual
accessibility, such as bolt holes.
9. Part Preparation
9.1 General—The surface of the ferromagnetic part to be examined should be essentially clean, dry, and free of contaminants such
as dirt, oil, grease, loose rust, loose mill sand, loose mill scale, lint, thick paint, welding flux/slag, and weld splatter that might
restrict particle movement. See 15.1.2 about applying dry particles to a damp/wet surface. When examining a local area, such as
a weld, the areas adjacent to the surface to be examined, as agreed by the contracting parties, must also be cleaned to the extent
necessary to permit detection of indications. See Appendix X6 for more information on steels.
9.1.1 Nonconductive Coatings—Thin nonconductive coatings, such as paint in the order of 1 or 2 mil (0.02 to 0.05 mm) will not
normally interfere with the formation of indications, but they must be removed at all points where electrical contact is to be made
for direct magnetization. Indirect magnetization does not require electrical contact with the part/piece. See Section 12.2. If a
nonconducting coating/plating is left on the area to be examined that has a thickness greater than 2 mil (0.05 mm), it must be
demonstrated that unacceptable discontinuities can be detected through the maximum thickness applied.
9.1.2 Conductive Coatings—A conductive coating (such as chrome plating and heavy mill scale on wrought products resulting
from hot forming operations) can mask discontinuities. As with nonconductive coatings, it must be demonstrated that the
unacceptable discontinuities can be detected through the coating.
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9.1.3 Residual Magnetic Fields—If the part/piece holds a residual magnetic field from a previous magnetization that will interfere
with the examination, the part must be demagnetized. See Section 18.
9.2 Cleaning Examination Surface—Cleaning of the examination surface may be accomplished by detergents, organic solvents,
or mechanical means. As-welded, as-rolled, as-cast, or as-forged surfaces are generally satisfactory, but if the surface is unusually
nonuniform, as with burned-in sand, a very rough weld deposit, or scale, interpretation may be difficult because of mechanical
entrapment of the magnetic particles. In case of doubt, any questionable area should be recleaned and reexamined (see 9.1).
9.2.1 Plugging and Masking Small Holes and Openings—Unless prohibited by the purchaser, small openings and oil holes leading
to obscure passages or cavities can be plugged or masked with a suitable nonabrasive material which is readily removed. In the
case of engine parts, the material must be soluble in oil. Effective masking must be used to protect components that may be
damaged by contact with the particles or particle suspension.
10. Sequence of Operations
10.1 Sequencing Particle Application and Establishing Magnetic Flux Field—The sequence of operation in magnetic particle
examination applies to the relationship between the timing and application of particles and establishing the magnetizing flux field.
Two basic techniques apply, that is, continuous (see 10.1.1 and 10.1.2) and residual (see 10.1.3), both of which are commonly
employed in industry.
10.1.1 Continuous Magnetization—Continuous magnetization is employed for most applications utilizing either dry or wet
particles and will provide higher magnetic field strengths, to aid indication formation better, than residual magentic fields. The
continuous method must be used when performing multidirectional magnetization. The sequence of operation for the dry and the
wet continuous magnetization techniques are significantly different and are discussed separately in 10.1.1.1 and 10.1.1.2.
10.1.1.1 Dry Continuous Magnetization Technique—Unlike a wet suspension, dry particles lose most of their mobility when they
contact the surface of a part. Therefore, it is imperative that the part/area of interest be under the influence of the applied magnetic
field while the particles are still airborne and free to be attracted to leakage fields. This dictates that the flow of magnetizing current
be initiated prior to the application of dry magnetic particles and terminated after the application of powder has been completed
and any excess has been blown off. Magnetizing with HW current and AC current provide additional particle mobility on the
surface of the part. Examination with dry particles is usually carried out in conjunction with prod-type or yoke localized
magnetizations, and buildup of indications is observed as the particles are being applied.
10.1.1.2 Wet Continuous Magnetization Technique—The wet continuous magnetization technique involves bathing the part with
the examination medium to provide an abundant source of suspended particles on the surface of the part and terminating the bath
application immediately prior to the termination of the magnetizing current. The duration of the magnetizing current is typically
on the order of ⁄2 s0.5 second for each magnetizing pulse (shot), with two or more shots given to the part. To insureensure that
indications are not washed away, the subsequent shots should follow the first while the particles are still mobile on the surface of
the part.
10.1.1.3 Polymer or Slurry Continuous Magnetization Technique—Prolonged or repeated periods of magnetization are often
necessary for polymer- or slurry-base suspensions because of slower inherent magnetic particle mobility in the high-viscosity
suspension vehicles.
10.1.2 True Continuous Magnetization Technique—In this technique, the magnetizing current is sustained throughout both the
processing and examination of the part.
10.1.3 Residual Magnetization Techniques:
10.1.3.1 Residual Magnetization—In this technique, the examination medium is applied after the magnetizing force has been
discontinued. It can be used only if the material being examined has relatively high retentivity so the residual leakage field will
be of sufficient strength to attract and hold the particles and produce indications. This technique may be advantageous for
integration with production or handling requirements or when higher than residual field strengths are not required to achieve
satisfactory results. When inducing circular fields and longitudinal fields of long pieces, residual fields are normally sufficient to
meet magnetizing requirements consistent with the requirements of Section 14. The residual method has found wide use examining
pipe and tubular goods. For magnetization requirements of oilfield tubulars, refer to Appendix X8. Unless demonstrations with
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typical parts indicate that the residual field has sufficient strength to produce relevant indications of discontinuities (see 20.8) when
the field is in proper orientation, the continuous method should be used.
11. Types of Magnetizing Currents
11.1 Basic Current Types—The four basic types of current used in magnetic particle testing to establish part magnetization are
alternating current (AC), half-wave rectified current (HW), full-wave rectified current (FW), and for a special application, DC.
11.1.1 Alternating Current (AC)—Part magnetization with alternating current is preferred for those applications where
examination requirements call for the detection of discontinuities, such as fatigue cracks, that are open to the surface to which the
magnetizing force is applied. Associated with AC is a “skin effect” that confines the magnetic field at or near to the surface of a
part. In contrast, both HW current and FW current produce a magnetic field having penetrating capabilities proportional to the
amount of applied current, which should be used when near-surface or inside surface discontinuities are of concern.
11.1.2 Half-Wave Rectified Current (HW)—Half-wave current is frequently used in conjunction with wet and dry particles because
the current pulses provide more mobility to the particles. This waveform is used with prods, yokes, mobile and bench units.
Half-wave rectified current is used to achieve depth of penetration for detection of typical discontinuities found in weldments,
forgings, and ferrous castings. As with AC for magnetization, single-phase current is utilized and the average value measured as
“magnetizing current.”
11.1.3 Full-Wave Rectified Current (FW)—Full-wave current may utilize single- or three-phase current. Three-phase current has
the advantage of lower line amperage draws, whereas single-phase equipment is less expensive. Full-wave rectified current is
commonly used when the residual method is to be employed. Because particle movement, either dry or wet is noticeably less,
precautions must be taken to ensure that sufficient time is allowed for formation of indications.
11.1.4 Direct Current (DC)—A bank of batteries, full-wave rectified AC filtered through capacitors or a DC generator produce
direct magnetizing current. They have largely given way to half-wave rectified or full-wave rectified DC except for a few
specialized applications, primarily because of
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