SIST-TP CEN/TR 17108:2017
(Main)Non-destructive testing - Lighting in penetrant and magnetic particle testing, good practice
Non-destructive testing - Lighting in penetrant and magnetic particle testing, good practice
This Technical Report describes the good practices of lighting under UV-A radiation and in white light as used for penetrant and magnetic particle testing.
This informative document deals with the irradiances and the illuminances used in penetrant and magnetic testing. It is intended for:
- manufacturers, encouraged to supply the criteria and the restrictions on use of their products, as well as detailed characteristics for the appropriate choice and the optimum use of sources available on the market,
- users, to make the best use of UV-A sources for efficient inspections and in the best conditions of use,
- supervision and training centres, which may knowingly design and optimally arrange the inspection areas, recommend the principles of visual ergonomics for ensuring the inspectors’ efficiency, comfort and safety.
Zerstörungsfreie Prüfung - Beleuchtung in Eindring- und Magnetpulverprüfung , bewährte Verfahren
Essais non destructifs - Bonnes pratiques déclairage lors des contrôles par ressuage et par magnétoscopie
Le présent rapport technique décrit les bonnes pratiques d’éclairage sous rayonnement UV-A et en lumière blanche utilisé en ressuage et magnétoscopie pour améliorer la probabilité de détection (POD).
Ce document à caractère informatif traite des éclairements énergétiques et lumineux utilisés en ressuage et magnétoscopie. Il est destiné à l’attention :
des fabricants, qui doivent être incités à fournir les critères et les limites d’utilisation de leurs produits ainsi que les caractéristiques détaillées en vue du choix approprié et de l’utilisation optimale des sources disponibles sur le marché ;
des utilisateurs, afin qu’ils puissent tirer le meilleur parti des sources d’éclairage pour des examens efficaces dans les conditions de travail ;
du personnel d’encadrement et de formation, qui peut agencer et ordonnancer de façon optimale les zones d'examen, recommander les principes d’ergonomie visuelle assurant efficacité, confort et sécurité aux contrôleurs.
Neporušitvene preiskave - Osvetlitev pri preiskavah s penetranti in magnetnimi delci, dobra praksa
To tehnično poročilo opisuje dobre prakse osvetlitve pri sevanju UV-A in beli svetlobi, ki se uporablja pri preiskavah s penetranti in magnetnimi delci. Ta informativni dokument obravnava sevanje in osvetlitve, ki se uporabljajo pri preiskavah s penetranti in magnetnimi delci. Namenjen je: – proizvajalcem, da predložijo kriterije in omejitve za uporabo svojih izdelkov ter podrobne značilnosti za ustrezno izbiro in optimalno uporabo virov, ki so na voljo na trgu, – uporabnikom da bi najboljše izkoristili vire UV-A za učinkovit nadzor in v najboljših pogojih uporabe, – centrom za nadzor in usposabljanje, ki lahko zavestno oblikujejo in optimalno uredijo področja nadzora ter priporočajo načela vizualne ergonomije za zagotovitev učinkovitosti, udobja in varnosti inšpektorjev.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CEN/TR 17108:2017
01-december-2017
Neporušitvene preiskave - Osvetlitev pri preiskavah s penetranti in magnetnimi
delci, dobra praksa
Non-destructive testing - Lighting in penetrant and magnetic particle testing, good
practice
Zerstörungsfreie Prüfung - Beleuchtung in Eindring- und Magnetpulverprüfung ,
bewährte Verfahren
(VVDLVQRQGHVWUXFWLIV%RQQHVSUDWLTXHVGpFODLUDJHORUVGHVFRQWU{OHVSDUUHVVXDJHHW
SDUPDJQpWRVFRSLH
Ta slovenski standard je istoveten z: CEN/TR 17108:2017
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
SIST-TP CEN/TR 17108:2017 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN/TR 17108:2017
CEN/TR 17108
TECHNICAL REPORT
RAPPORT TECHNIQUE
June 2017
TECHNISCHER BERICHT
ICS 19.100
English Version
Non-destructive testing - Lighting in penetrant and
magnetic particle testing, good practice
Essais non destructifs - Bonnes pratiques d'éclairage Zerstörungsfreie Prüfung - Beleuchtung in Eindring-
lors des contrôles par ressuage et par magnétoscopie und Magnetpulverprüfung, bewährte Verfahren
This Technical Report was approved by CEN on 28 May 2017. It has been drawn up by the Technical Committee CEN/TC 138.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 17108:2017 E
worldwide for CEN national Members.
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Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Fluorescent techniques, inspection booth, lights and visual ergonomics . 5
4.1 Lights: UV-A beam spectral characteristics . 5
4.1.1 General . 5
4.1.2 Symmetry of the spectrum around the centroid wavelength . 5
4.1.3 Unwanted visible light of the UV-A spectrum: limitation of the emission > 380 nm . 6
4.1.4 Radiometric specifications: UV-A/violet ratio . 6
4.1.5 Thermal management (cooling), sustaining performances . 8
4.2 UV-A beam geometrical characteristics . 9
4.2.1 General . 9
4.2.2 Geometric consideration for use . 9
4.2.3 Large parts . 10
4.2.4 Small parts . 10
4.3 Identification and repair . 11
4.4 Health and safety when using UV-A sources . 11
4.4.1 Precautions for use . 11
4.4.2 Warning panels . 11
4.4.3 Eyewear . 13
4.5 Visual ergonomics . 14
4.5.1 General . 14
4.5.2 Visual adaptation, general . 14
4.5.3 Visible light before inspection . 15
4.5.4 Visible light during inspection . 16
4.5.5 Visible light after inspection: focus recovery/preserving . 17
4.5.6 Transition zones: avoid visual tiredness . 18
4.5.7 General irradiance . 18
5 Colour and luminous contrast method . 18
5.1 White beam spectral characteristics . 18
5.2 Viewing of coloured materials: choosing the source. 19
5.3 Precautions for use . 20
5.3.1 High-luminance type LED sources . 20
5.3.2 Eyewear . 22
5.4 Illuminance levels of the inspection area and of the surrounding area: visual
ergonomics . 23
5.4.1 General . 23
5.4.2 Fixed inspection areas . 23
5.4.3 On-site inspections . 23
5.4.4 Case study . 23
6 Measurements . 25
6.1 Radiometers and luxmeters characteristics/specifications . 25
6.2 Irradiance measurement . 25
7 Actinic Blue . 26
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European foreword
This document (CEN/TR 17108:2017) has been prepared by Technical Committee CEN/TC 138 “Non-
destructive testing”, the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
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1 Scope
This Technical Report describes the good practices of lighting under UV-A radiation and in white light
as used for penetrant testing (PT) and magnetic particle testing (MT) for improved probability of
detection (POD).
This informative document deals with the irradiance and the illuminance used in PT and MT. It is
intended for:
— manufacturers, who are encouraged to supply the criteria and the restrictions on use of their
products, as well as detailed characteristics for the appropriate choice and the optimum use of
sources available on the market;
— users, to enable them to make the best use of lighting sources for efficient inspection in working
conditions;
— supervision and training personnel, who may design and optimally arrange inspection areas,
recommend the principles of visual ergonomics for ensuring inspector efficiency, comfort and
safety.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 170, Personal eye-protection — Ultraviolet filters — Transmittance requirements and recommended
use
EN 12464-1, Light and lighting — Lighting of work places — Part 1: Indoor work places
CEN/TR 16638, Non-destructive testing — Penetrant and magnetic particle testing using blue light
EN 62471, Photobiological safety of lamps and lamp systems (IEC 62471)
EN ISO 12706, Non-destructive testing — Penetrant testing — Vocabulary (ISO 12706)
EN ISO 12707, Non-destructive testing — Magnetic particle testing — Vocabulary (ISO 12707)
ISO/CIE 19476 (CIE S 023/E), Characterization of the performance of illuminance meters and luminance
meters
3 Terms and definitions
For the purpose of this document, the terms and definitions given in EN ISO 12706, EN ISO 12707 and
the following apply.
3.1
centroid wavelength
mathematically weighted mean output wavelength sharing in two equal parts the spectrum emitted by
a source
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3.2
colour rendering index
CRI
degree of agreement between the colour appearance of objects illuminated by the considered source
and that of the same objects illuminated by a reference illuminant, under specified viewing conditions
3.3
colour temperature
Tcp
temperature of a planckian (or black body) radiator, the radiation of which has the same chromaticity
as a given stimulus, expressed in Kelvin (K)
3.4
LEDs
light-emitting diodes
3.5
maculopathy
impaired function of the macula which degrades colour vision and leads to a decrease of visual acuity
3.6
mesopic vision
twilight or medium vision between the photopic vision and the scotopic vision
3.7
photopic vision
daytime or high-luminance vision where only the cone optic cells are active
Note 1 to entry: In photopic vision, the 555 nm wavelength (green-yellow) is the human eyes maximum
sensitivity.
3.8
scotopic vision
night-time or in low luminance vision where only the rod optic cells are active
Note 1 to entry: In scotopic vision, the 505 nm (blue-green or turquoise.) wavelength is the human eyes maximum
sensitivity.
4 Fluorescent techniques, inspection booth, lights and visual ergonomics
4.1 Lights: UV-A beam spectral characteristics
4.1.1 General
UV-A LED lamps technology needs to be understood since they are used for lighting in NDT methods
using fluorescent materials, ISO 3059 deals with requirements but the following clauses provide
technical explanation and guidance for the use of UV-A lamps in NDT.
4.1.2 Symmetry of the spectrum around the centroid wavelength
The optical brighteners used in penetrants and some fluorescent pigments used in the MT detection
media usually absorb 80 % of the radiation energy between 340 nm and 380 nm. Therefore for UV-A
LEDs a symmetrical, Gaussian emission spectrum around the peak output wavelength is recommended.
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The optical brighteners used in penetrants and some fluorescent pigments used in the MT detection
media have an absorption peak between 360 nm and 370 nm. The centroid wavelength of the UV-A
source shall be close to the peak absorption so that the radiation is more efficient to excite the dyes of
the fluorescent penetrants and the pigments of the fluorescent detection media.
These conditions are met when the centroid wavelength is close to the central wavelength (emission
peak).
4.1.3 Unwanted visible light of the UV-A spectrum: limitation of the emission > 380 nm
The eye is sensitive to wavelengths greater than 380 nm. The 380 nm to 420 nm area (violet light and
extreme violet) is emitted as a stray light by most of UV-A source.
This violet can cause, as UV-A, visual blue haze by exciting some proteins in the eye.
Vision of the direct violet and indirect blue haze effect leads to increasing the noise which impairs the
detection of indications.
Manufacturer shall minimize the emission of violet light by carefully selecting the LEDs, the filter, and
using a well-controlled thermal management system to prevent any drift leading to an increase of
unwanted violet output.
This visible violet to which the eye is sensitive is not fully filtered by Wood filters nor by all the UV-
blocking goggles; this comes at the cost of the contrast at the inspection stage on all types of metal parts
(except yellow metals that naturally absorb violet and blue).
Bright surfaces strongly reflect violet light, requiring the inspector to guide the relative position of the
parts to avoid this reflection; matt surfaces turn to a purplish colour background regardless of the
orientation of the beam.
4.1.4 Radiometric specifications: UV-A/violet ratio
Violet light is the 380 nm 420 nm area.
In order to take into account the data described in the previous clause, the manufacturer or the supplier
shall state the measurements relevant to the UV-A/ violet ratio in the product data sheet (user manual,
procedure, product manual, etc.).
The result may be given in the form of a ratio calculated by analysing the spectrum with a
spectrophotometer positioned at the beam centre, then, by discriminating the UV-A area up to 380 nm
and the violet area, 380 nm to 420 nm.
For professional purposes, UV-A sources should be used so as to minimize their effect, as follows:
— a Wood filter or similar, to remove violet as much as possible, shall be an integral part of the source.
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Key
X wavelength (nm)
Y relative scale
1 green curve: UV-A spectra with Wood filter in the violet range
2 purple curve: UV-A spectra without Wood filter in the violet range
Figure 1 — Example of reduction of the violet light 380 nm to 420 nm by a source fit with a Wood
filter
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Key
X wavelength (nm)
Y relative irradiance
1 central wavelength: 368,9 nm
2 centroid wavelength: 369,5 nm
3 full width half maximum: 10,9 nm
NOTE The left side in light violet colour corresponds to UV-A and the right side in dark violet colour to visible
violet
Figure 2 — Example of measured spectrum
4.1.5 Thermal management (cooling), sustaining performances
A poor thermal management will cause beam instability, spectrum shift with violet increase and power
loss.
In case of LED sources, the elements ensuring the extraction of calories shall be maintained in an
optimal operation condition (e.g. dust filter replacement, removing dust deposits on coolers, renewal of
thermal paste during LED maintenance etc.).
An automatic circuit-breaker system shall be built-in to take action in case of overheating; leading to a
non-compliance of the beam (wavelength shift beyond 370 nm and violet versus UV-A ratio increase for
LEDs).
Regarding LED sources: during their use, no decrease of power, likely to reduce the irradiance without
notice by the operator, shall ever be acceptable as a means to prevent overheating.
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For UV source not intended to be used continuously the manufacturer shall state the maximum time to
be used.
4.2 UV-A beam geometrical characteristics
4.2.1 General
The variety of inspection circumstances and the variety of part sizes and localizations, such as large
individual parts or grapes of small sized parts, need our attention to choose adequate lighting scenari; a
good choice leads to visual performance enhancement and better POD.
4.2.2 Geometric consideration for use
The pattern and the beam size of the source in use should be fitted to the surface of the area inspected
on the parts and the arrangement thereof (if parts are displayed as “clusters” or as “trays” of several
parts). The way the human eye works and, particularly, the roles of the fovea and of the peripheral
vision shall be taken into account during inspection.
Therefore, several types of beam patterns should be considered: wide or narrow, with sharp or
progressive edges to adapt the beam to the spatial conditions and orientation on the inspection zone to
use the full capability of detection of the human vision.
A practical test of the source for the specific application is always helpful before choosing the beam
pattern.
The field of vision may be considered as three areas:
1) The fovea is the central area of the macula (see Figure 3). It is located on the optical axis of the eye
where only the cone optic cells are tightly present. At this level, the vision is more accurate and
more detailed than for the rest of the retina;
2) The near peripheral vision utilizes rod and cone sensors and provides a more general vision
capability. This is a much wider area of the visual field than the foveal region;
3) The far peripheral vision is the remaining angular range of vision.
Key
1 fovea / macula
2 near peripheral vision
3 far peripheral vision
Figure 3 — Illustration of the vision areas
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Key
4 UV-A wide type beam with progressive edge
5 UV-A narrow type beam with sharp edges
Figure 4 — UV-A beam patterns
4.2.3 Large parts
For large parts, the peripheral vision is used to guide the central vision towards points on which
attention should be focused; a wide-pattern beam with progressive edges will then be preferred.
Figures 5a and 5b give an example of NDT application: inspection of large areas; an indication seen in
the near peripheral vision “catches the eye” and initiates the movement of the eye towards a vision by
the fovea.
a) Intermediate casing of civil aeroengine b) Aircraft structural component
Figure 5
4.2.4 Small parts
When inspecting specific areas of large parts or small parts one by one, the foveal vision prevails; the
eye is used almost exclusively for its central vision.
A medium-wide uniform beam pattern with sharp edges is the optimal configuration as the right
illumination conditions will be reached inside the beam.
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Figure 6 shows an example of NDT application: thorough inspection of small to medium-sized parts,
analysis of indications.
Figure 6 — Carbide ball bearings and nut (aeronautical parts)
4.3 Identification and repair
Each series of the type of source gets a unique trade name.
Any change made to the source likely to modify the data described in this document shall require a
change in the identification of the series of source type.
The characteristics of a repaired source shall be identical to those of the series of the original type
source. Otherwise, any deviation shall be documented.
4.4 Health and safety when using UV-A sources
4.4.1 Precautions for use
The triplet UV-A/O /infrared shall be avoided as much as possible in order to limit the fluorescence
2
fading of the indications especially for PT. This situation occurs when the area under inspection is
irradiated by a spectrum containing UV-A and infrared radiations, and hot air-flow coming from the
source further directed towards the same area.
For discharge lamps, the cooling air-flow when existing should not be directed towards the part in the
axis of the optical beam as UV-A and infrared radiations are present.
Cumulative doses of extreme violet (near UV-A) are one of the causes for maculopathy, retinal diseases
and early cataract.
4.4.2 Warning panels
In order to warn operators against the hazards inherent to UV-radiation, warning signs are placed:
a) at the entrance of the area where UV-A radiation is emitted (pictograms and wording warning
against hazards and indicating suitable protective equipment);
b) visible in the vicinity of the UV-A source, as a reminder.
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Figure 7 — Examples of warning signs: UV-blocking safety goggles shall be worn
Figure 8 — Examples of warning signs: Warning Non-ionizing UV radiation
When wearing protective equipment is mandatory, it shall be mentioned in every relevant documents.
Key
X wavelength (nm)
Y spectral efficiency
Figure 9 — Spectral weighing function Suv(λ) for UV radiation hazard according to the
IEC/EN 62641
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4.4.3 Eyewear
As specified in 4.1.3, violet glare impairs the quality of detection and the operator’s comfort. Any means
to lower the visibility of violet is allowed, if this does not prevent the proper viewing of indications
(specific violet-non-reflective goggles, for instance).
The UV-A radiation shall be blocked by personal protective equipment such as goggles or eyeshade, as
described in EN 170.
Some suppliers make available violet blocking lenses, keeping the colour of the glass in class 0 -
previously class A - (no colour) or treated-in-the mass lenses. Such lenses are recommended for
spectacle wearers with correction.
For inspectors without any visual correction, simple UV-blocking polycarbonate safety glasses are
suitable for UV-A protection (preventing blue haze due to fluorescence inside the eye itself). As regards
violet-blocking goggles, only models with a specific additive to polycarbonate are satisfactory.
a) Goggles fully blocking UV-A radiation and partially b) Representation of the filtration of a UV-A tubular
violet light source
Key
X wavelength (nm)
Y transmission (%)
Figure 10 — Example of filtration of a UV-A tubular source by suitable goggles (green curve),
which fully block UV-A radiation and partially violet light (to be preferred to the red curve
blocking UV-A only)
Glasses partially blocking the deep visible violet, in addition to blocking UV-A, have a very light pale
yellow tan. These glasses shall be considered as uncoloured.
It is important to consider the strong sensitivity of pseudo-phakic inspectors (wearing a transparent
lens implant, for example, after cataract surgery) to wavelengths between 380 nm and 420 nm. Indeed,
a “natural” adult lens, because of its yellowing, is less permeable to such wavelengths. In this case,
glasses that block UV-A radiation, but also violet light, are required to maintain a highly contrasted
vision under UV-A radiation.
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4.5 Visual ergonomics
4.5.1 General
This clause deals with photo-biological pieces of information, advice for operations in fluorescent
penetrant inspection (FPI) lines and MT stations.
Visual ergonomics are of importance as human being is the final link to the detection and decision
chain, the better the "in situ" conditions, the better POD.
Eye and brain interactions have to be enhanced and best practice encouraged leading to efficient,
reliable and reproducible inspections.
4.5.2 Visual adaptation, general
Conditions conducive to pupil dilation should be promoted according to 4.5.2 and 4.5.3 as they allow for
the habituation of the retina receptors before performing the inspection. This is achieved by minimizing
as much as possible the vision of light sources emitting blue/turquoise colours while leaving enough
time for the retina to operate in mesopic vision.
Key
X time in darkness (minutes)
Y sensitivity to light (log units)
1 cones
2 rods
Figure 11 — Desaturation curve of rods and cones
Viewing fluorescent indications calls upon mesopic conditions: both scotopic and photopic vision
systems are active, taking respectively into account the rod and cone receptors.
The "cones” system, which is less sensitive to light than the “rods” system, is “de-saturated” faster than
the “rods” system, which is most sensitive to light events at very low levels. In the case of an inspection
of tiny indications, visual habituation times over 5 min are desirable, ideally, 10 min, in order to have
both systems desaturated and fully efficient to see small amounts of light emitted by faint indications.
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This being industrially questionable, refer to 4.5.1 to start counting this time from the entry into the
transition area, if duties of preparation prior to inspection are carried out in dimmed lighting.
A reference test block according to EN ISO 3452-1, B.3.2 and/or EN ISO 9934-2, B.1, along with the
linked reference picture, if this one may be viewed under UV-A radiation, may be used to validate the
inspector’s effective visual adaptation.
4.5.3 Visible light before inspection
It is recommended to prepare the eyes for the photopic-to-mesopic transition. A transition area, as
described in 4.5.6 is preferred.
Pupillary dilatation which is an integral part of the eye adaptation to darkness shall be facilitated.
Visible light containing significant proportions of blue and turquoise shall therefore be avoided
according to Figure 12.
Key
X wavelength (nm)
Y relative sensitivity (log)
Z relative 482 nomogram
Figure 12 — Diagram showing the importance of the blue/turquoise wavelengths to control the
pupillary diameter
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Key
X
wavelength (nm)
Figure 13 — Relative proportions of wavelengths in two fluorescent penetrants with a peak and
a wide emission in the turquoise range (500 nm)
Figure 13 shows the penetrants colorimetry with the blue plus turquoise plus yellow colours. Too high
a brightness of these colours is not suitable to prepare the vision before an inspection. A satisfactory
state of cleanliness in FPI lines and magnetic benches will be maintained by regularly cleaning the walls
stained by green splashes of fluorescent materials. During water rinse in PT, a too-high irradiance shall
be avoided to prevent the penetrant on part surface from emitting a too-high disturbing fluorescence
brightness.
4.5.4 Visible light during inspection
Light sources such as emergency exit lights, indicators on machines, electrical panels or any other
source of visible light in a room should not be visible. The luminance - especially that due to screens
(PLCs or computers) - shall remain balanced (low) compared to the darkness of the workstations.
Fluorescent dirt (see 4.5.7) and the strongly-fluorescent plastic cables are disturbing sources of light.
During an inspection, any source of blue light should be avoided: the pupillary dilatation is controlled
by the “S” cones and circadian r
...
SLOVENSKI STANDARD
kSIST-TP FprCEN/TR 17108:2017
01-marec-2017
Neporušitveno preskušanje - Osvetlitev pri preskušanju s penetranti in z
magnetnimi delci, dobra praksa
Non-destructive testing - Lighting in penetrant and magnetic particle testing, good
practice
Zerstörungsfreie Prüfung - Beleuchtung in Eindring- und Magnetpulverprüfung ,
bewährte Verfahren
(VVDLVQRQGHVWUXFWLIV%RQQHVSUDWLTXHVGpFODLUDJHORUVGHVFRQWU{OHVSDUUHVVXDJHHW
SDUPDJQpWRVFRSLH
Ta slovenski standard je istoveten z: FprCEN/TR 17108
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
kSIST-TP FprCEN/TR 17108:2017 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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kSIST-TP FprCEN/TR 17108:2017
FINAL DRAFT
TECHNICAL REPORT
FprCEN/TR 17108
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
February 2017
ICS 19.100
English Version
Non-destructive testing - Lighting in penetrant and
magnetic particle testing, good practice
Essais non destructifs - Bonnes pratiques d¿éclairage Zerstörungsfreie Prüfung - Beleuchtung in Eindring-
lors des contrôles par ressuage et par magnétoscopie und Magnetpulverprüfung , bewährte Verfahren
This draft Technical Report is submitted to CEN members for Vote. It has been drawn up by the Technical Committee CEN/TC
138.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a Technical Report.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TR 17108:2017 E
worldwide for CEN national Members.
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Contents
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 5
4 Fluorescent techniques, inspection booth, lights and visual ergonomics . 6
4.1 Lights: UV-A beam spectral characteristics . 6
4.1.1 General . 6
4.1.2 Symmetry of the spectrum around the centroid wavelength . 6
4.1.3 Unwanted visible light of the UV-A spectrum: limitation of the emission > 380 nm . 6
4.1.4 Radiometric specifications: UV-A/violet ratio . 6
4.1.5 Thermal management, sustaining performances (cooling) . 8
4.2 UV-A beam geometrical characteristics . 9
4.2.1 General . 9
4.2.2 Geometric consideration for use . 9
4.2.3 Large parts . 10
4.2.4 Small parts . 10
4.3 Identification and repair . 11
4.4 Health and safety when using UV-A sources . 11
4.4.1 Precautions for use . 11
4.4.2 Warning panels . 11
4.4.3 Eyewear . 13
4.5 Visual ergonomics . 14
4.5.1 General . 14
4.5.2 Visual adaptation, general . 14
4.5.3 Visible light before inspection . 15
4.5.4 Visible light during inspection . 16
4.5.5 Visible light after inspection: focus recovery/preserving . 17
4.5.6 Transition zones: avoid visual tiredness . 18
4.5.7 General irradiance . 18
5 Colour and luminous contrast method . 18
5.1 White beam spectral characteristics . 18
5.2 Viewing of coloured media: choosing the source . 19
5.3 Precautions for use . 20
5.3.1 High-luminance type LED sources . 20
5.3.2 Eyewear . 22
5.4 Illuminance levels of the inspection area and of the surrounding area: visual
ergonomics . 23
5.4.1 General . 23
5.4.2 Fixed inspection areas . 23
5.4.3 On-site inspections . 23
5.4.4 Case study . 24
6 Measurements . 25
6.1 Radiometers and luxmeters characteristics/specifications . 25
6.2 Irradiance measurement . 25
7 Actinic Blue . 26
Bibliography . 27
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European foreword
This document (FprCEN/TR 17108:2017) has been prepared by Technical Committee CEN/TC 138
“Non-destructive testing”, the secretariat of which is held by AFNOR.
This document is currently submitted to the Vote.
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1 Scope
This Technical Report describes the good practices of lighting under UV-A radiation and in white light
as used for penetrant and magnetic particle testing for improved probability of detection (POD).
This informative document deals with the irradiance and the illuminance used in penetrant and
magnetic testing. It is intended for:
— manufacturers, who are to encouraged to supply the criteria and the restrictions on use of their
products, as well as detailed characteristics for the appropriate choice and the optimum use of
sources available on the market;
— users, to enable them to make the best use of lighting sources for efficient inspection in working
conditions;
— supervision and training personnel, who may design and optimally arrange inspection areas,
recommend the principles of visual ergonomics for ensuring inspector efficiency, comfort and
safety.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 170, Personal eye-protection - Ultraviolet filters - Transmittance requirements and recommended use
EN 12464-1, Light and lighting - Lighting of work places - Part 1: Indoor work places
EN ISO 12707, Non-destructive testing - Magnetic particle testing - Vocabulary (ISO 12707)
EN ISO 12706, Non-destructive testing - Penetrant testing - Vocabulary (ISO 12706)
IEC/EN 62471, Photobiological safety of lamps and lamp systems
ISO/CIE 19476 (CIE S 023/E), Characterization of the performance of illuminance meters and luminance
meters
CEN/TR 16638, Non-destructive testing - Penetrant and magnetic particle testing using blue light
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3 Terms and definitions
For the purpose of this document, the terms and definitions given in EN ISO 12706, EN ISO 12707 and
the following apply.
3.1
centroid wavelength
mathematically weighted mean output wavelength sharing in two equal parts the spectrum emitted by
a source
3.2
colour rendering index
CRI
Ra
degree of agreement between the colour appearance of objects illuminated by the considered source
and that of the same objects illuminated by a reference illuminant, under specified viewing conditions
3.3
colour temperature
Tcp
temperature of a planckian (or black body) radiator, the radiation of which has the same chromaticity
as a given stimulus, expressed in Kelvin (K)
3.4
LEDs
light-emitting diodes
3.5
maculopathy
impaired function of the macula which degrades colour vision and leads to a decrease of visual acuity
3.6
mesopic vision
twilight or medium vision between the photopic vision and the scotopic vision
3.7
photopic vision
daytime or high-luminance vision where only the cone optic cells are active
Note 1 to entry: In photopic vision, the 555 nm wavelength (green-yellow) is the human eyes maximum
sensitivity.
3.8
scotopic vision
night-time or in low luminance vision where only the rod optic cells are active
Note 1 to entry: In scotopic vision, the 505 nm (blue-green or turquoise.) wavelength is the human eyes maximum
sensitivity.
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4 Fluorescent techniques, inspection booth, lights and visual ergonomics
4.1 Lights: UV-A beam spectral characteristics
4.1.1 General
UV-A LED lamps technology needs to be understood as used for lighting in NDT methods using
fluorescent materials, ISO 3059 deals with the requirements but the following clauses provide technical
explanation and guidance for the use of UV-A lamps in NDT.
4.1.2 Symmetry of the spectrum around the centroid wavelength
The fluorescent dyes used in penetrant and magnetic particle testing materials usually absorb 80 % of
the radiation energy between 340 nm and 380 nm. Therefore for UV-A LEDs a symmetrical, Gaussian
emission spectrum around the peak output wavelength is recommended.
Fluorescent dyes have an absorption peak between 360 nm and 370 nm. The centroid wavelength of
the UV-A source shall be close to the peak absorption so that the radiation is more efficient to excite the
dyes of the fluorescent penetrants and the pigments of the fluorescent detection media.
These conditions are met when the centroid wavelength is close to the central wavelength (emission
peak).
4.1.3 Unwanted visible light of the UV-A spectrum: limitation of the emission > 380 nm
The eye is sensitive to wavelengths greater than 380 nm. The 380 nm to 420 nm area (violet light and
extreme violet) is emitted as a stray light by any UV-A source.
This violet can cause, as UV-A, visual blue haze by exiting some proteins in the eye.
Vision of direct violet and indirect blue haze effect lead in increasing the noise in the signal/noise ratio
that impairs indications detection.
Manufacturer shall minimize the emission of violet light by carefully selecting the LEDs, the filter, and
using a well-controlled thermal management system to prevent any drift leading to an increase of
unwanted violet output.
This visible violet to which the eye is sensitive is not fully filtered by wood’s filters nor by all the UV-
blocking goggles; this comes at the cost of:
— the contrast at the inspection stage on all types of metal parts (except yellow metals that naturally
absorb violet and blue).
The bright surfaces strongly reflect violet light, requiring the inspector to guide the relative position of
the parts to avoid this reflection; matt surfaces turn to a purplish colour background regardless of the
orientation of the beam.
4.1.4 Radiometric specifications: UV-A/violet ratio
Violet light is the 380 nm 420 nm area.
In order to take into account the data described in the previous clause. The manufacturer or the
supplier shall state the measurements relevant to the UV-A/ violet ratio in the product data sheet (user
manual, procedure, product manual, etc.).
The result may be given in the form of a ratio calculated by analysing the spectrum with a
spectrophotometer positioned at the beam centre, then, by discriminating the UV-A area up to 380 nm
and the violet area, 380 nm to 420 nm.
For professional purposes, UV-A sources should be used so as to minimize their effect, as follows:
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— a Wood filter or similar, to remove violet as much as possible, shall be an integral part of the source.
Key
X wavelength (nm)
Y relative scale
1 Green curve: UV-A spectra with Wood filter in the violet range
2 Purple curve: UV-A spectra without Wood filter in the violet range
Figure 1 — Example of reduction of the violet light 380 nm to 420 nm by source fit with a Wood
filter
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Key
X wavelength (nm)
Y relative irradiance
1 Central wavelength: 368,9 nm
2 Centroid wavelength: 369,5 nm
3 Full width half maximum: 10,9 nm
NOTE The left side in light violet colour corresponds to UV-A and the right side in dark violet colour to visible
violet
Figure 2 — Example of measured spectrum
4.1.5 Thermal management, sustaining performances (cooling)
A poor thermal management will cause beam instability, spectrum shift with violet increase and power
loss.
Maintenance of the elements ensuring the extraction of calories (e.g. dust filter replacement, removing
dust deposits on coolers, renewal of thermal paste during LED maintenance etc.).
An automatic circuit-breaker system shall be built-in to take action in case of overheating; leading to a
non-compliance of the beam (wavelength shift beyond 370 nm and violet versus UV-A ratio increase for
LEDs).
Regarding LED sources: during their use, no decrease of power, likely to reduce the irradiance without
notice by the operator, shall ever be acceptable as a means to prevent overheating.
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For UV source not intended to be used continuously the manufacturer shall state the maximum on time
to be used.
4.2 UV-A beam geometrical characteristics
4.2.1 General
The variety of inspections circumstances and the variety of parts size and localizations, such as large
individual parts or grapes of small sized parts, need our attention to choose adequate lighting scenarios;
a good choice lead to visual performance enhancement and better probability of detection.
4.2.2 Geometric consideration for use
The pattern and the beam size of the source in use should be fitted to the surface of the area inspected
on the parts and the arrangement thereof (if parts are displayed as “clusters” or as “trays” of several
parts). The way the human eye works and, particularly, the roles of the fovea and of the peripheral
vision shall be taken into account during inspection.
Therefore, several types of beam patterns should be considered: wide or narrow, with sharp or
progressive edges to adapt the beam to the spatial conditions and orientation on the inspection zone to
use the full capability of detection of the human vision.
A practical test of the source for the specific application is always helpful before choosing the beam
pattern.
The field of vision may be considered as three areas:
1) The fovea is the central area of the macula (see Figure 3). It is located on the optical axis of the eye
where only the cone optic cells are tightly present. At this level, the vision is more accurate and
more detailed than for the rest of the retina;
2) The near peripheral vision utilizes rod and cone sensors and provides a more general vision
capability. This is a much wider area of the visual field than the foveal region;
3) The far peripheral vision is the remaining angular range of vision.
Key
1 fovea / macula
2 near peripheral vision
3 far peripheral vision
Figure 3 — Illustration of the vision areas
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Key
4 UV-A wide type beam with progressive edge
5 UV-A narrow type beam with sharp edges
Figure 4 — UV-A beam patterns
4.2.3 Large parts
For large parts, the peripheral vision is used to guide the central vision towards points on which
attention should be focused; a wide-pattern beam with progressive edges will then be preferred.
Figures 5a and 5b gives an example of NDT application: inspection of large areas; an indication seen in
the near peripheral vision “catches the eye” and initiates the movement of the eye towards a vision by
the fovea.
a) Intermediate casing of civil aeroengine b) Aircraft structural component
Figure 5
4.2.4 Small parts
When inspecting specific areas of large parts or small parts one by one, the foveal vision prevails; the
eye is used almost exclusively for its central vision.
A medium-wide uniform beam pattern with sharp edges is the optimal configuration as the right
illumination conditions will be reached inside the beam.
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Figure 6 shows an example of NDT application: thorough inspection of small to medium-sized parts,
analysis of indications.
Figure 6 — Carbide ball bearings and nut (aeronautical parts)
4.3 Identification and repair
Each series of the type of source gets a unique trade name.
Any change made to the source likely to modify the data described in this document shall require a
change in the identification of the series of source type.
The characteristics of a repaired source shall be identical to those of the series of the original type
source. Otherwise, any deviation shall be documented.
4.4 Health and safety when using UV-A sources
4.4.1 Precautions for use
The triplet UV-A/O /infrared shall be avoided as much as possible in order to limit the fluorescence
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fading of the indications especially for penetrant testing. This situation occurs when the area under
inspection is irradiated by a spectrum containing UV-A and infrared radiations, and hot air-flow coming
from the source further directed towards the same area.
For discharge lamps, the cooling air-flow when existing should not be directed towards the part in the
axis of the optical beam as UV-A and infrared radiations are present.
Cumulative doses of extreme violet (near UV-A) are one of the causes for maculopathy, retinal diseases
and early cataract.
4.4.2 Warning panels
In order to warn operators against the hazards inherent to UV-radiation, warning signs are placed:
a) at the entrance of the area where UV-A radiation is emitted (pictograms and wording warning
against hazards and indicating suitable protective equipment);
b) visible in the vicinity of the UV-A source, as a reminder.
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Figure 7 — Examples of warning signs: UV-blocking safety goggles shall be worn
Figure 8 — Examples of warning signs: Warning Non-ionizing UV radiation
When wearing protective equipment is mandatory, it shall be mentioned in every relevant documents.
Key
X wavelength (nm)
Y spectral efficiency
Figure 9 — Spectral weighing function Suv(λ) for UV radiation hazard according to the
IEC/EN 62641
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4.4.3 Eyewear
As specified in 4.1.3, violet glare impairs the quality of detection and the operator’s comfort. Any means
to lower the visibility of violet is allowed, if this does not prevent the proper viewing of indications
(specific violet-non-reflective goggles, for instance).
The UV-A radiation shall be blocked by personal protective equipment such as goggles or eyeshade, as
described in EN 170.
Some suppliers make available violet blocking lenses, keeping the colour of the glass in class 0 -
previously class A - (no colour) or treated-in-the mass lenses. Such lenses are recommended for
spectacle wearers with correction.
For inspectors without any visual correction, simple UV-blocking polycarbonate safety glasses are
suitable for UV-A protection (preventing blue haze due to fluorescence inside the eye itself). As regards
violet-blocking goggles, only models with a specific additive to polycarbonate are satisfactory.
a) b)
Key
X wavelength (nm)
Y transmission (%)
Figure 10 — Example of filtration of a UV-A tubular source by suitable goggles (green curve),
which fully block UV-A radiation and partially violet light (to be preferred to the red curve
blocking UV-A only)
Glasses partially blocking the deep visible violet, in addition to blocking UV-A, have a very light pale
yellow tan. These glasses shall be considered as uncoloured.
It is important to consider the strong sensitivity of pseudo-phakic inspectors (wearing a transparent
lens implant, for example, after cataract surgery) to wavelengths between 380 nm and 420 nm. Indeed,
a “natural” adult lens, because of its yellowing, is less permeable to such wavelengths. In this case,
glasses that block UV-A radiation, but also violet light, are required to maintain a highly- contrasted
vision under UV-A radiation.
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4.5 Visual ergonomics
4.5.1 General
This clause deals with photo-biological pieces of information, advices for operations in FPI (fluorescent
penetrant inspection) lines and magnetic particle testing stations.
Visuals ergonomics are of importance as human being is the final linkage is the detection and decision
chain, the best conditions are ‘in situ’ better the POD is.
Eye and brain interactions have to be enhanced and best practise encouraged leading in efficient,
reliable, reproducible inspections.
4.5.2 Visual adaptation, general
Conditions conducive to pupil dilation should be promoted according to 4.5.3 and 4.5.2. as they allow
for the habituation of the retina receptors before performing the inspection. This is achieved by
minimizing as much as possible the vision of light sources emitting blue/turquoise colours while
leaving enough time for the retina to operate in mesopic vision.
Key
X time in darkness (minutes)
Y sensitivity to light (log units)
1 cones
2 rods
Figure 11 — Desaturation curve of rods and cones
Viewing fluorescent indications calls upon mesopic conditions: both scotopic and photopic vision
systems are active, taking respectively into account the rod and cone receptors.
The “cones” system -less sensitive to light than rods- is “de-saturated” faster than the “rods” one, the
most sensitive to light event at very low levels. In the case of an inspection of tiny indications, visual
habituation times over 5 min are desirable, ideally, 10 min, in order to have both systems desaturated
and fully efficient to see small amounts of light emitted by faint indications.
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This being industrially questionable refers to 4.5.1 to start counting this time from the entry into the
transition area, if duties of preparation prior to inspection are carried out in dimmed lighting.
A reference test block according to EN ISO 3452-1, B.3.2 may be used to validate the inspector’s
effective visual adaptation, along with the linked reference picture, if this one may be used under UV-A
radiation.
4.5.3 Visible light before inspection
It is recommended to prepare the eyes for the photopic-to-mesopic transition. A transition area, as
described in 4.5.1 is preferred.
Pupillary dilatation which is an integral part of the eye adaptation to darkness shall be facilitated.
Visible light containing significant proportions of blue and turquoise shall therefore be avoided
according to Figure 12.
Key
X wavelength (nm)
Y relative sensitivity (log)
Z relative 482 nomogram
Figure 12 — Diagram showing the importance of the blue/turquoise wavelengths to control the
pupillary diameter
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Key
X
wavelength (nm)
Figure 13 — Relative proportions of wavelengths in two fluorescent penetrants with a peak and
a wide emission in the turquoise range (500 nm)
Figure 13 shows the penetrants colorimetry with the blue plus turquoise plus yellow colours. Too high
a brightness of these colours is not suitable to prepare the vision before an inspection. A satisfactory
state of cleanliness in FPI lines and magnetic benches will be maintained by regularly cleaning the walls
stained by green splashes of fluorescent materials. During water rinse in PT, a too-high irradiance shall
be avoided to prevent the surface part from emitting a too-high disturbing fluorescence brightness.
4.5.4 Visible light during inspection
Light sources such as emergency exit lights, indicators on machines, electrical panels or any other
source of visible light in a room should not be visible. The light luminance - especially that due to
screens (PLCs or computers) - shall remain balanced (low) compared to the darkness of the
workstations.
Fluorescent
...
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