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ASTM G46-94(1999)

(Guide)

Standard Guide for Examination and Evaluation of Pitting Corrosion

Standard Guide for Examination and Evaluation of Pitting Corrosion

SCOPE
1.1 This guide is intended to assist in the selection of procedures that can be used in the identification and examination of pits and in the evaluation of pitting (See Terminology G15) corrosion to determine the extent of its effect.  
1.2 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

Status
Historical
Publication Date
09-Jan-1999
ICS
77.060 - Corrosion of metals
Technical Committee
G01 - Corrosion of Metals
Drafting Committee
G01.05 - Laboratory Corrosion Tests
Current Stage
Ref Project

Relations

Replaced By
ASTM G46-94(2005) - Standard Guide for Examination and Evaluation of Pitting Corrosion
Effective Date
01-May-2005
Referred By
ASTM G189-07(2021)e1 - Standard Guide for Laboratory Simulation of Corrosion Under Insulation
Effective Date
10-Jan-1999
Referred By
ASTM G48-11(2020)e1 - Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
Effective Date
10-Jan-1999
Referred By
ASTM G16-13(2019) - Standard Guide for Applying Statistics to Analysis of Corrosion Data
Effective Date
10-Jan-1999
Referred By
ASTM G199-09(2020)e1 - Standard Guide for Electrochemical Noise Measurement
Effective Date
10-Jan-1999
Referred By
ASTM G87-02(2023) - Standard Practice for Conducting Moist SO<inf>2</inf> Tests
Effective Date
10-Jan-1999
Referred By
ASTM G1-03(2017)e1 - Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
Effective Date
10-Jan-1999
Referred By
ASTM G170-06(2020)e1 - Standard Guide for Evaluating and Qualifying Oilfield and Refinery Corrosion Inhibitors in the Laboratory
Effective Date
10-Jan-1999
Referred By
ASTM G150-18 - Standard Test Method for Electrochemical Critical Pitting Temperature Testing of Stainless Steels and Related Alloys
Effective Date
10-Jan-1999
Referred By
ASTM G184-06(2020)e1 - Standard Practice for Evaluating and Qualifying Oil Field and Refinery Corrosion Inhibitors Using Rotating Cage
Effective Date
10-Jan-1999
Referred By
ASTM G107-95(2020)e1 - Standard Guide for Formats for Collection and Compilation of Corrosion Data for Metals for Computerized Database Input
Effective Date
10-Jan-1999
Referred By
ASTM G31-21 - Standard Guide for Laboratory Immersion Corrosion Testing of Metals
Effective Date
10-Jan-1999
Referred By
ASTM G162-18 - Standard Practice for Conducting and Evaluating Laboratory Corrosion Tests in Soils
Effective Date
10-Jan-1999
Referred By
ASTM G217-16(2022) - Standard Guide for Corrosion Monitoring in Laboratories and Plants with Coupled Multielectrode Array Sensor Method
Effective Date
10-Jan-1999
Referred By
ASTM C1617-19 - Standard Practice for Quantitative Accelerated Laboratory Evaluation of Extraction Solutions Containing Ions Leached from Thermal Insulation on Aqueous Corrosion of Metals
Effective Date
10-Jan-1999

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ASTM G46-94(1999) - Standard Guide for Examination and Evaluation of Pitting CorrosionASTM G46-94(1999) - Standard Guide for Examination and Evaluation of Pitting Corrosion
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ASTM G46-94(1999) - Standard Guide for Examination and Evaluation of Pitting Corrosion
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Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:G46–94 (Reapproved 1999)
Standard Guide for
1
Examination and Evaluation of Pitting Corrosion
ThisstandardisissuedunderthefixeddesignationG 46;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope apparentlocationofpits.Itisoftenadvisabletophotographthe
corroded surface at this point so that it can be compared with
1.1 This guide is intended to assist in the selection of
the clean surface after the removal of corrosion products.
procedures that can be used in the identification and examina-
4.1.1 If the metal specimen has been exposed to an un-
tion of pits and in the evaluation of pitting (See Terminology
known environment, the composition of the corrosion products
G 15) corrosion to determine the extent of its effect.
may be of value in determining the cause of corrosion. Follow
1.2 This standard does not purport to address all of the
recommended procedures in the removal of particulate corro-
safety concerns, if any, associated with its use. It is the
sion products and reserve them for future identification (see
responsibility of the user of this standard to establish appro-
NACE Standard RP-01-73).
priate safety and health practices and determine the applica-
4.1.2 To expose the pits fully, use recommended cleaning
bility of regulatory limitations prior to use.
procedures to remove the corrosion products and avoid solu-
2. Referenced Documents tions that attack the base metal excessively (see Practice G 1).
It may be advisable during cleaning to probe the pits with a
2.1 ASTM Standards:
2
pointed tool to determine the extent of undercutting or subsur-
E 3 Methods of Preparation of Metallographic Specimens
face corrosion (Fig. 1). However, scrubbing with a stiff bristle
G 1 Practice for Preparing, Cleaning, and Evaluating Cor-
3
brush will often enlarge the pit openings sufficiently by
rosion Test Specimens
removal of corrosion products, or undercut metal to make the
G 15 Terminology Relating to Corrosion and Corrosion
3
pits easier to evaluate.
Testing
4.1.3 Examine the cleaned metal surface under ordinary
G 16 Guide forApplying Statistics toAnalysis of Corrosion
3
light to determine the approximate size and distribution of pits.
Data
Follow this procedure by a more detailed examination through
2.2 NationalAssociationofCorrosionEngineersStandard:
a microscope using low magnification (203).
RP-01-73 Collection and Identification of Corrosion Prod-
4
4.1.4 Determine the size, shape, and density of pits.
ucts
4.1.4.1 Pits may have various sizes and shapes. A visual
3. Significance and Use
examinationofthemetalsurfacemayshowaround,elongated,
or irregular opening, but it seldom provides an accurate
3.1 It is important to be able to determine the extent of
indication of corrosion beneath the surface. Thus, it is often
pitting, either in a service application where it is necessary to
necessary to cross section the pit to see its actual shape and to
predict the remaining life in a metal structure, or in laboratory
determine its true depth. Several variations in the cross-
test programs that are used to select the most pitting-resistant
sectioned shape of pits are shown in Fig. 1.
materials for service.
4.1.4.2 It is a tedious job to determine pit density by
4. Identification and Examination of Pits
counting pits through a microscope eyepiece, but the task can
be made easier by the use of a plastic grid. Place the grid,
4.1 Visual Inspection—A visual examination of the cor-
containing 3 to 6-mm squares, on the metal surface. Count and
rodedmetalsurfaceisusuallybeneficial,andthisisdoneunder
record the number of pits in each square, and move across the
ordinary light, with or without the use of a low-power
grid in a systematic manner until all the surface has been
magnifying glass, to determine the extent of corrosion and the
covered. This approach minimizes eyestrain because the eyes
can be taken from the field of view without fear of losing the
1
This practice is under the jurisdiction of ASTM Committee G-1 on Corrosion
area of interest.
of Metals, and is the direct responsibility of Subcommittee G01.05 on Laboratory
4.1.5 Metallographic Examination—Select and cut out a
Corrosion Tests.
representative portion of the metal surface containing the pits
Current edition approved Feb. 15, 1994. Published April 1994. Originally
published as G 46 – 76. Last previous edition G 46 – 92. and prepare a metallographic specimen in accordance with the
2
Annual Book of ASTM Standards, Vol 03.01.
recommended procedures given in Methods E 3. Examine
3
Annual Book of ASTM Standards, Vol 03.02.
4
Insert in Materials Protection an
...

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4.1 Polythionic acids are chemically described as H2SxO6, where x is usually 3, 4, or 5 (1)3 though can be more than 50 (2). These acid environments provide a way of evaluating the resistance of stainless steels and related alloys to intergranular stress corrosion cracking. Failure is accelerated by the presence of increasing amounts of intergranular precipitate. Results for the polythionic acid test have not been correlated exactly with those of intergranular corrosion tests (Test Methods G28). Also, this test may not be relevant to stress corrosion cracking in chlorides or caustic environments.  
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1.3 This practice can be applied to wrought products, castings, and weld metal of stainless steels or other related materials to be used in environments containing sulfur or sulfides. Other materials capable of being sensitized can also be tested in accordance with this test.  
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3.1 Moist air containing sulfur dioxide quickly produces easily visible corrosion on many metals in a form resembling that occurring in industrial environments. It is therefore a test medium well suited to detect pores or other sources of weakness in protective coatings and deficiencies in corrosion resistance associated with unsuitable alloy composition or treatments.  
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1.1 This practice covers procedures for making and using U-bend specimens for the evaluation of stress-corrosion cracking in metals. The U-bend specimen is generally a rectangular strip that is bent 180° around a predetermined radius and maintained in this constant strain condition during the stress-corrosion test. Bends slightly less than or greater than 180° are sometimes used. Typical U-bend configurations showing several different methods of maintaining the applied stress are shown in Fig. 1.  
FIG. 1 Typical Stressed U-bends  
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5.1 Autoclave tests are commonly used to evaluate the corrosion performance of metallic and non-metallic materials under simulated HP and HTHP service conditions. Examples of service environments in which HP and HTHP corrosion tests have been used include chemical processing, petroleum production and refining, food processing, pressurized cooling water, electric power systems, and aerospace propulsion.  
5.2 For the applications of corrosion testing listed in 5.1, the service environment involves handling corrosive and potentially hazardous media under conditions of high pressure or high temperature, or both. The temperature and pressure, among other parameters, usually drive the composition and properties of the aqueous phase and, hence, the severity of the corrosion process. Consequently, the laboratory evaluation of corrosion severity cannot be performed in conventional low pressure glassware without making potentially invalid assumptions as to the potential effects of high temperature and pressure on corrosion severity.  
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1.2 The procedures and methods in this guide are applicable for conducting mass loss corrosion, localized corrosion, and electrochemical tests as well as for use in environmentally induced cracking tests that need to be conducted under HP or HTHP conditions.  
1.3 The primary purpose for this guide is to promote consistency of corrosion test results. Furthermore, this guide will aid in the comparison of corrosion data between laboratories or testing organizations that utilize different equipment.  
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
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Standard Guide for Examination and Evaluation of Pitting Corrosion

SIGNIFICANCE AND USE
4.1 It is important to be able to determine the extent of pitting, either in a service application in which it is necessary to predict the remaining life in a metal structure, or in laboratory test programs that are used to select the most pitting-resistant materials for service. The purpose of the study is crucial in determining the appropriate examination and evaluation steps.  
4.2 Some typical purposes of laboratory tests include, but are not limited to, evaluating performance of alloys, determining whether an alloy is resistant to the environment, evaluating how environmental conditions including corrosion inhibitor affect or prevent pitting, and evaluating whether a lot of metal is sufficiently resistant for its use in a particular application or environment.  
4.3 Some typical purposes of field studies include, but are not limited to, determining if pits are likely to grow and cause leak or release of process fluid, and assisting a determination of whether to replace or repair damage from pits (remaining life assessment).
SCOPE
1.1 This guide covers the selection of procedures that can be used in the examination and evaluation of pitted metals. These procedures include both nondestructive and destructive approaches.  
1.2 The procedures covered in this guide include those that may be used in laboratory evaluations of corroded metal specimens and field examinations and inspections.  
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.3.1 Exception—In X1.2.1, mils per year (MPY) are regarded as standard for the target corrosion rate.  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
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SIGNIFICANCE AND USE
5.1 The bent-beam specimen is designed for determining the stress-corrosion behavior of alloy sheets and plates in a variety of environments. The bent-beam specimens are designed for testing at stress levels below the elastic limit of the alloy. For testing in the plastic range, U-bend specimens should be employed (see Practice G30). Although it is possible to stress bent-beam specimens into the plastic range, the stress level cannot be calculated for plastically-stressed three- and four-point loaded specimens as well as the double-beam specimens. Therefore, the use of bent-beam specimens in the plastic range is not recommended for general use.
SCOPE
1.1 This practice covers procedures for designing, preparing, and using bent-beam stress-corrosion specimens.  
1.2 Different specimen configurations are given for use with different product forms, such as sheet or plate. This practice is applicable to specimens of any metal that are stressed to levels less than the elastic limit of the material, and therefore, the applied stress can be accurately calculated or measured (see Note 1). Stress calculations by this practice are not applicable to plastically stressed specimens.  
Note 1: It is the nature of these practices that only the applied stress can be calculated. Since stress-corrosion cracking is a function of the total stress, for critical applications and proper interpretation of results, the residual stress (before applying external stress) or the total elastic stress (after applying external stress) should be determined by appropriate nondestructive methods, such as X-ray diffraction (1).2  
1.3 Test procedures are given for stress-corrosion testing by exposure to gaseous and liquid environments.  
1.4 The bent-beam test is best suited for flat product forms, such as sheet, strip, and plate. For plate material the bent-beam specimen is more difficult to use because more rugged specimen holders must be built to accommodate the specimens. A double-beam modification of a four-point loaded specimen to utilize heavier materials is described in 10.5.  
1.5 The exposure of specimens in a corrosive environment is treated only briefly since other practices deal with this aspect, for example, Practices D1141, G30, G36, G44, G50, and G85. The experimenter is referred to ASTM Special Technical Publication 425 (2).  
1.6 The bent-beam practice generally constitutes a constant strain (deflection) test. Once cracking has initiated, the state of stress at the tip of the crack as well as in uncracked areas has changed, and therefore, the known or calculated stress or strain values discussed in this practice apply only to the state of stress existing before initiation of cracks.  
1.7 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.8  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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. (For more specific safety hazard information see Section 7 and 12.1.)  
1.9 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.

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ASTM
ASTM G186-05(2021)(Test Method)
Standard Test Method for Determining Whether Gas-Leak-Detector Fluid Solutions Can Cause Stress Corrosion Cracking of Brass Alloys

SIGNIFICANCE AND USE
5.1 Brass components are routinely used in compressed gas service for valves, pressure regulators, connectors and many other components. Although soft brass is not susceptible to ammonia SCC, work-hardened brass is susceptible if its hardness exceeds about 54 HR 30T (55HRB) (Rockwell scale). Normal assembly of brass components should not induce sufficient work hardening to cause susceptibility to ammonia SCC. However, it is has been observed that over-tightening of the components will render them susceptible to SCC, and the problem becomes more severe in older components that have been tightened many times. In this test, the specimens are obtained in the hardened condition and are strained beyond the elastic limit to accelerate the tendency towards SCC.  
5.2 It is normal practice to use LDFs to check pressurized systems to assure that leaking is not occurring. LDFs are usually aqueous solutions containing surfactants that will form bubbles at the site of a leak. If the LDF contains ammonia or other agent that can cause SCC in brass, serious damage can occur to the system that will compromise its safety and integrity.  
5.3 It is important to test LDFs to assure that they do not cause SCC of brass and to assure that the use of these products does not compromise the integrity of the pressure containing system.  
5.4 It has been found that corrosion of brass is necessary before SCC can occur. The reason for this is that the corrosion process results in cupric and cuprous ions accumulating in the electrolyte. Therefore, adding copper metal and cuprous oxide (Cu2O) to the aqueous solution accelerates the SCC process if agents that cause SCC are present. However, adding these components to a solution that does not cause SCC will not make stressed brass crack.  
5.5 Repeated application of the solution to the specimen followed by a drying period causes the components in the solution to concentrate thereby further increasing the rate of cracking. This also simulates se...
SCOPE
1.1 This test method covers an accelerated test method for evaluating the tendency of gas leak detection fluids (LDFs) to cause stress corrosion cracking (SCC) of brass components in compressed gas service.  
1.2 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.  
1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 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.

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