Liquid penetrant testing (PT) is the surface NDT method that works on every weld material — from carbon steel pipe joints to austenitic stainless structural welds and aluminium aerospace components. Where magnetic particle testing stops at the magnetic boundary, PT works by capillary action alone: it enters surface-breaking cracks regardless of material permeability. Yet PT is routinely misapplied in weld inspection — insufficient dwell times that miss tight hydrogen-induced cracks, developers applied before the penetrant is fully removed, and post-weld inspections skipped entirely on aluminium welds where MT would not work anyway. This guide covers everything a welding QA engineer or Level 2 inspector needs to apply PT correctly: the physics of capillary action, the EN ISO 3452-1 six-stage procedure, EN ISO 23277 acceptance levels, and the ISO 3834 documentation chain that audit teams check.
Penetrant testing of welds at a glance
PT in welding is penetrant testing (also called liquid penetrant or dye penetrant testing): a liquid soaks into imperfections open to the surface of the clean weld, the excess is removed, and a developer draws the penetrant back out as a visible indication. It works on any non-porous metal and finds only surface-breaking imperfections. Three ISO standards cover it:
- Method — ISO 3452-1: the general principles of the test, from penetrant systems and process steps to the test report. Penetrant materials and their sensitivity levels are classified in ISO 3452-2.
- Viewing — ISO 3059:2012: colour-contrast inspection needs 500 lx or more at the test surface; fluorescent inspection needs UV-A irradiance of 10 W/m² or more with no more than 20 lx of visible light.
- Acceptance — ISO 23277:2015, last confirmed by ISO in 2025. The test surface is the weld metal plus 10 mm of parent metal on each side (5.1). Table 1 limits:
| Indication | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| Linear (length > 3 × width), length l | ≤ 2 mm | ≤ 4 mm | ≤ 8 mm |
| Non-linear (length ≤ 3 × width), major dimension d | ≤ 4 mm | ≤ 6 mm | ≤ 8 mm |
Levels 2 and 3 can be specified with the suffix X (2X, 3X): every linear indication detected is then assessed to level 1. ISO 23277 does not cover grouped indications, and it points to ISO 17635 for how its levels relate to the ISO 5817 and ISO 10042 quality levels.
Key Takeaways
- Penetrant testing detects surface-breaking discontinuities only — internal defects require PAUT or RT.
- PT applies to any non-porous material: stainless, aluminium, titanium, nickel alloys, and carbon steel — making it the usual surface NDT for austenitic and non-ferrous welds.
- The six-stage sequence — pre-clean → penetrant → dwell → removal → developer → inspect — must not be shortened; dwell time is the most frequent compliance failure in production inspection.
- Governed by EN ISO 3452-1 (examination method), ISO 3059 (viewing conditions), EN ISO 23277 (weld acceptance levels), and ASTM E1417 in North America.
- Fluorescent PT is the more sensitive choice for small imperfections; ISO 23277 Annex A recommends it (or a high-sensitivity colour-contrast system) for acceptance level 1.
- Personnel are commonly certified to ISO 9712 (SNT-TC-1A in the USA), and the written NDT procedure is approved before production inspection starts.
- PT reports are part of the weld quality records that ISO 3834 and EN 1090 audits sample — keep them traceable to the weld map, with instrument calibration and penetrant batch.
Table of Contents
- How Liquid Penetrant Testing Works
- The Six-Stage PT Procedure
- Standards That Govern PT of Welds
- PT Acceptance Criteria: EN ISO 23277
- Common Failure Modes and Fixes
- PT vs Other Surface NDT Methods
- Documentation and ISO 3834 Compliance
- Frequently Asked Questions
How Liquid Penetrant Testing Works
Liquid penetrant testing works by exploiting capillary action: a low-viscosity, high-wettability liquid enters tight surface-breaking discontinuities under the combined effect of surface tension and gravity. When a developer is applied after the excess penetrant is removed, it reverses the capillary gradient — drawing the penetrant back out and spreading it into a visible (or UV-fluorescent) indication that is wider than the original crack, making it detectable by the human eye.
Three properties determine PT sensitivity:
| Property | Effect on detection |
|---|---|
| Penetrant viscosity | Lower viscosity helps entry into tight cracks |
| Surface tension | Must be lower than the weld surface energy to wet it completely |
| Fluorescence quantum yield | Higher for Type 1 fluorescent penetrant vs Type 2 visible dye |
Material applicability: PT has no magnetic permeability requirement. It works on carbon steel, low-alloy steel, austenitic and duplex stainless steels, aluminium alloys, titanium, nickel alloys, and copper alloys. The only constraint is surface porosity — porous sintered materials and rough as-welded surfaces produce high background levels that can mask real indications.
Detection limits: what PT can find depends on the penetrant sensitivity level (ISO 3452-2), the surface condition and the technique (ISO 23277, clause 4). Rough or irregular surfaces — undercut, rippling, spatter — raise the background and lower the probability of detecting small imperfections. PT does not detect imperfections that are not open to the surface and must never be specified as a substitute for UT or RT for internal inspection.
Comparison with MT: on ferromagnetic carbon steel, magnetic particle testing is generally faster (no dwell time overhead) and more sensitive to near-surface HAZ cracks. PT and MT are complementary methods, not substitutes — PT covers the full material range, while MT adds near-surface volumetric sensitivity on ferritic steels.
The Six-Stage PT Procedure
EN ISO 3452-1 defines the mandatory sequence for weld PT examination. Each stage has minimum performance requirements that must be documented in the written NDT procedure approved before production inspection begins.
Stage 1: Pre-Cleaning
The weld surface must be free of rust, scale, coatings, oil, water, and heat tint that could block penetrant entry or produce false indications. Accepted methods:
- Mechanical: wire brushing or grinding (coarse surfaces entrap developer and raise the background)
- Chemical: solvent wiping with acetone or isopropanol, acid pickling for oxide scale
- Blast cleaning: for heavily scaled welds, always followed by solvent wipe
After aqueous cleaning, dry the surface completely so residual water does not block crack openings and stop the penetrant entering.
Avoid heavy grinding or polishing of the inspection zone just before PT: smeared metal can close crack openings. Where local grinding is used to improve the surface, clean the area before testing.
Stage 2: Penetrant Application
Apply penetrant by spray, brush, or immersion to cover the entire inspection zone. Keep the test surface within the temperature range the procedure and the penetrant product are qualified for; testing outside it needs a procedure qualified for that temperature.
Stage 3: Dwell Time
The penetrant must remain on the surface undisturbed for the penetration (dwell) time specified in the approved procedure, chosen for the penetrant product, the surface temperature and the imperfections sought. Longer dwell times are typically used for:
- Tight stress-corrosion cracking or hydrogen-induced cold cracking
- Surface temperatures at the low end of the qualified range
- High-alloy materials with low surface energy (nickel alloys, titanium)
- Fatigue cracks subject to repeated loading that tends to close crack faces
Cutting dwell time to increase throughput is a frequent root cause of missed indications in production PT.
Stage 4: Excess Penetrant Removal
The removal method must match the penetrant product type. Over-removal strips penetrant from inside defects; under-removal leaves background staining that masks real indications.
| PT Method | Removal technique | Notes |
|---|---|---|
| Method A — water-washable | Water spray or rinse at the pressure and temperature set in the procedure | Fast for production; risk of over-removal on shallow defects |
| Method B — post-emulsifiable, lipophilic | Emulsifier applied for specified contact time, then rinsed | Time-critical emulsification step |
| Method C — solvent-removable | Dry wipe first, then minimal damp solvent wipe — never soak | Best for field and repair inspection |
| Method D — post-emulsifiable, hydrophilic | Water pre-rinse, hydrophilic emulsifier, final water rinse | Production batch inspection |
Stage 5: Developer Application
Apply developer immediately after removal and allow it to dry before inspection. The developer must coat the surface uniformly:
- Non-aqueous wet developer (NAWD): spray-apply a thin, uniform coat; do not double-coat
- Dry powder: normally used with fluorescent penetrant systems, not for colour-contrast inspection; check that it belongs to the qualified penetrant system
- Aqueous wet: for large-batch production inspection; dry before inspection
Respect the development time in the procedure. ISO 23277 (5.2) requires the final sizing of each indication after the designated minimum development time and before the indication has spread so far that it no longer represents the imperfection.
Stage 6: Inspection and Recording
Viewing conditions are set in ISO 3059:2012:
| Penetrant type | Light source | Minimum level at test surface |
|---|---|---|
| Colour contrast | White light | 500 lx or more |
| Fluorescent | UV-A, peak at (365 ± 5) nm | 10 W/m² or more; visible light 20 lx or less |
Light meter and UV-A radiometer calibration must be current and documented. Indications are classified as linear (length more than three times the width) or non-linear, sized, and compared against the acceptance level per ISO 23277. Normally, acceptable indications are not recorded (ISO 23277, 5.1), although many contracts ask for them.
Standards That Govern PT of Welds
EN ISO 3452-1 — PT Method Standard
EN ISO 3452-1 (Non-destructive testing — Penetrant testing — Part 1: General principles) is the primary international method standard. It sets the general principles of the test: penetrant systems, the process steps and the test report. Viewing conditions come from ISO 3059. Companion parts of the ISO 3452 series cover testing of penetrant materials (Part 2), reference test blocks (Part 3), and equipment (Part 4).
ISO 9712 is the usual personnel certification scheme for PT; the contract or application standard sets the level required for each task.
EN ISO 23277 — Acceptance Levels for PT of Welds
EN ISO 23277 (Non-destructive testing of welds — Penetrant testing — Acceptance levels) (second edition 2015, last confirmed by ISO in 2025) is the acceptance standard for indications from surface-breaking imperfections in metallic welds examined by PT. See the acceptance criteria section below for the complete decision table.
ASTM E1417 and North American References
ASTM E1417 (Standard Practice for Liquid Penetrant Testing) is the North American practice for penetrant testing. Under ASME, Section V Article 6 covers the examination method and the construction code (for example Section VIII) sets acceptance; AWS D1.1 has its own clauses for structural welds. Take each clause from the edition named in the contract. Personnel in the USA typically qualify under the ASNT SNT-TC-1A recommended practice.
Industry Guidance
TWI Global maintains a comprehensive PT knowledge base covering penetrant product selection, sensitivity levels, and common process failure modes. BINDT publishes personnel competency requirements aligned with EN ISO 9712 for the UK and European market. The NDT Resource Center at nde-ed.org provides detailed educational content on the physics of capillary action and PT mechanism.
PT Acceptance Criteria: EN ISO 23277
ISO 23277:2015 defines three acceptance levels, 1 (most stringent) to 3, for indications in metallic welds. The level comes from the contract or the application standard; ISO 17635 gives the matching level for welds made to an ISO 5817 or ISO 10042 quality level. The test surface is the weld metal plus 10 mm of parent metal on each side (5.1).
| Indication type (ISO 23277:2015 Table 1) | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| Linear, accepted if length l | ≤ 2 mm | ≤ 4 mm | ≤ 8 mm |
| Non-linear, accepted if major dimension d | ≤ 4 mm | ≤ 6 mm | ≤ 8 mm |
With the suffix X (level 2X or 3X), every linear indication detected is assessed to level 1, but ISO 23277 warns that indications smaller than the original level may have a low probability of detection. Indications approximately in line and separated by less than the length of the smaller one are assessed as a single continuous indication (5.1). Grouped indications are not covered by the standard.
Linear vs non-linear definition: an indication longer than three times its width is linear (ISO 23277, 3.1); one with a length less than or equal to three times its width is non-linear (3.2).
Sizing protocol: ISO 23277 assesses the size of the indication, not of the imperfection behind it (5.1). Make the final measurement after the designated minimum development time and before the indication has degenerated (5.2). ISO 23277 Annex A recommends a fine surface for level 1, a smooth surface for level 2 and the general as-welded surface for level 3.
Cracks: ISO 23277 judges indications by size, not by imperfection type, and application standards normally do not accept cracks. A crack-like linear indication should be reviewed by the responsible NDT Level 3 and welding engineer before any repair decision. Where the product specification permits, local grinding can reduce or remove the cause; the area is then re-tested with the same penetrant system and technique (5.3). If there is doubt about the classification, a visual weld inspection per EN ISO 17637 and cross-sectional metallography should be considered.
For context on how PT acceptance levels relate to the broader ISO 5817 weld quality level system for visual examination, note that these are separate acceptance gates: EN ISO 23277 governs PT indication disposition, while ISO 5817 governs geometrical weld imperfection limits for visual inspection. Both must be satisfied for a weld to be accepted.
Common Failure Modes and Fixes
These are the root causes of PT failures in weld production inspection — both false negatives (missed real defects) and false positives (false indications that trigger unnecessary repairs).
Missed Indications (False Negatives)
| Failure mode | Root cause | Corrective action |
|---|---|---|
| Tight cracks not detected | Dwell time too short, or surface too cold for the penetrant product | Apply the full procedure dwell time; bring the surface into the qualified temperature range |
| Background masking real indications | Excess penetrant not fully removed | Follow Method C strictly: dry wipe first, then minimal solvent damp wipe — never soak |
| No indication from open porosity | Penetrant evaporated before developer applied | Reduce time between removal and developer; avoid direct sunlight on the part |
| HAZ toe cracks missed | Penetrant does not fully wet the tight weld toe geometry | Use a lower-viscosity Type 1 penetrant product; apply in two overlapping passes |
| Root cracks not found from outside | Root inaccessible to surface PT | Specify internal bore PT or combine with PAUT for full root coverage |
False Calls (False Positives)
| False call type | Cause | Fix |
|---|---|---|
| Linear indications along grinding direction | Mechanical smearing from aggressive pre-cleaning grinder | Follow grinding with solvent wipe; reduce final grit size |
| Indication at weld toe not reproducible | Oxide pocket, not a crack — clears on re-clean and re-test | Pickle, re-clean, and re-test; persistent indication on re-test requires repair evaluation |
| Widespread fluorescent background on part | Incompatible penetrant and developer from different product families | Always use a matched family from the same manufacturer; verify compatibility certificate |
| Indications on re-test at different location | Developer coat too thick and spreading indication | Reduce developer layer thickness; use a properly adjusted spray can or electrostatic gun |
Always perform a full re-test of any indication before initiating a weld repair. Re-testing confirms whether the indication is reproducible and genuine. Repairing a false call introduces additional grinding, re-welding, and post-repair NDT — and the repair HAZ may itself require examination, compounding the cost.
PT vs Other Surface NDT Methods
Choosing between PT, magnetic particle testing (MT), and visual inspection (VT) depends on material, defect type, and production logistics.
| Criterion | PT | MT | VT |
|---|---|---|---|
| Material applicability | All non-porous: steel, SS, Al, Ti, Ni alloys | Ferromagnetic only: carbon steel, low-alloy steel, ferritic SS | All |
| Detection | Surface-breaking only | Surface and near-surface | Surface only |
| Sensitivity to tight surface cracks | High (Type 1 fluorescent: very high) | Very high on ferritic steel | Low |
| Field portability | High (aerosol spray products available) | High (portable electromagnetic yoke) | High |
| Primary governing standard | EN ISO 3452-1 / ASTM E1417 | EN ISO 17638 / ASTM E709 | EN ISO 17637 |
| Personnel requirement | ISO 9712 Level 2 PT | ISO 9712 Level 2 MT | VT may not require 9712 unless specified |
Decision rule for ferritic carbon steel welds: specify MT as the primary surface NDT method — it is faster, more sensitive to near-surface HAZ hydrogen cracking, and avoids the overhead of penetrant dwell time. Reserve PT for weld root runs accessible only from inside (boring or nozzle connections) and for confirmation of ambiguous MT indications.
Decision rule for austenitic stainless, aluminium, or titanium welds: specify PT — MT is physically inapplicable to non-ferromagnetic materials. Where the specification requires them, use certified low-halogen products for stainless steel in process plant service, so the inspection consumables do not contaminate the surface.
Combined PT and PAUT protocol: for high-integrity welds — pressure vessels to ASME VIII, nuclear components, pipeline girth welds to API 1104 — a dual-method NDT protocol combining PT (surface-breaking cracks) and PAUT (volumetric soundness) on the same inspection visit provides the widest defect coverage within a single mobilisation.
For a structured view of all welding defects, their causes, and acceptance criteria, see the defect reference guide which maps each defect type to the applicable NDT method and relevant acceptance standard.
Documentation and ISO 3834 Compliance
Under EN ISO 3834-2 comprehensive quality requirements and EN 1090 CE marking, PT reports are part of the weld quality records the manufacturer keeps and auditors sample. Take the retention period from the contract and the application standard.
Each PT inspection report must contain at minimum:
- NDT procedure reference number, revision, and approval status
- Contract reference and unique weld joint identifier (traceability to the weld map or isometric)
- Examination date, time, and ambient temperature at time of examination
- Inspector name, ISO 9712 qualification level, certificate number, and expiry date
- Penetrant product family, type (1 or 2), method (A–D), manufacturer, and batch number
- Surface temperature measured at time of penetrant application (calibrated thermometer reference)
- Actual penetrant dwell time and developer development time (not nominal from the procedure)
- Light meter or UV-A radiometer reading with instrument calibration certificate reference
- All indications found: location by reference to weld coordinate system, orientation, length, width, classification (linear/non-linear/crack)
- Acceptance level applied per EN ISO 23277 and accept/reject decision
- Inspector signature and counter-signature where required by the inspection plan
Work only to a written, approved NDT procedure. An inspector who follows an unapproved procedure — or makes undocumented field adaptations to dwell time or removal method — creates a non-conformance under the fabrication quality plan even if the welds are physically sound.
Digital weld quality management platforms can auto-populate the weld identity, inspection date, and ambient conditions fields from an in-process monitoring backbone, reducing transcription errors. Thermal monitoring systems record interpass temperatures alongside the weld identity, generating an audit-ready record that covers both heat input compliance and the pre-inspection thermal state of the weld. The Therness weld monitoring platform integrates thermal and visual sensor data into a unified traceability chain, so that PT reports and process records reference the same weld identifier throughout the QMS.
For fabricators seeking to structure their complete NDT documentation, the guide to ISO 3834 and EN 1090 welding traceability with thermography explains how digital records from different NDT and process monitoring methods are consolidated into a single audit-ready file. The full range of Therness thermal and visual monitoring systems feeds those records automatically.
Frequently Asked Questions
What is a PT test in welding?
PT in welding stands for penetrant testing, also called liquid penetrant or dye penetrant testing (LPT, DPT). A coloured or fluorescent liquid is applied to the clean weld and left to soak into imperfections open to the surface; the excess is removed and a developer draws the penetrant back out as a visible indication. PT finds only surface-breaking imperfections such as cracks, surface porosity and lack of fusion open to the surface, and it works on any non-porous metal, including austenitic stainless steel and aluminium, where magnetic particle testing cannot be used. The method is ISO 3452-1; acceptance of indications in welds is ISO 23277.
Which standards govern penetrant testing of welds?
ISO 3452-1 sets the general principles of the penetrant test: penetrant systems, process steps and the test report. ISO 3452-2 classifies penetrant materials and their sensitivity levels. Viewing conditions come from ISO 3059. ISO 23277 sets acceptance levels 1, 2 and 3 for indications in welds, and ISO 17635 relates them to the ISO 5817 and ISO 10042 quality levels. In North America ASTM E1417 is the penetrant testing practice; under ASME, Section V Article 6 covers the examination method and the construction code sets acceptance. Take each clause from the edition named in the contract.
What defects can penetrant testing detect in welds?
PT detects surface-breaking discontinuities: longitudinal and transverse cracks, toe cracks in the heat-affected zone (HAZ), root cracks where the root is accessible, crater cracks, lack of fusion open to the surface, surface porosity, and cold laps. It does not detect internal defects such as buried porosity, slag inclusions, or lack of fusion below the surface. For internal volumetric inspection, PAUT or RT is required.
What are the ISO 23277 acceptance levels for PT indications in welds?
ISO 23277:2015 Table 1 accepts linear indications (length more than three times the width) up to 2 mm at level 1, 4 mm at level 2 and 8 mm at level 3, and non-linear indications up to a major dimension of 4 mm, 6 mm and 8 mm. Levels 2 and 3 can carry the suffix X, which means every linear indication detected is assessed to level 1. The test surface is the weld metal plus 10 mm of parent metal on each side. Grouped indications are not covered.
What is a linear indication in penetrant testing?
Under ISO 23277 (3.1) a linear indication is one whose length is more than three times its width; any other indication is non-linear (3.2). Linear indications are judged by their length: up to 2 mm at level 1, 4 mm at level 2 and 8 mm at level 3. Indications roughly in line and separated by less than the length of the smaller one count as one continuous indication (5.1).
What is the dwell time for penetrant testing of welds?
ISO 23277 does not fix a dwell time. The penetration (dwell) time and the development time are set in the written procedure to ISO 3452-1, for the penetrant product and the surface temperature in use. ISO 23277 (5.2) requires the final sizing of each indication after the designated minimum development time and before the indication has spread so far that it no longer represents the imperfection. Cutting the dwell time to speed up inspection is a frequent cause of missed tight cracks.
Can penetrant testing be applied to austenitic stainless steel welds?
Yes. Unlike magnetic particle testing (MT), PT does not depend on magnetic permeability, so it applies to austenitic stainless steels (grades 304, 316, 321), aluminium alloys, nickel alloys, titanium and copper alloys. For stainless steel in process plant service, specifications often require low-halogen penetrant products, so the inspection consumables do not contaminate the surface.
Is fluorescent PT more sensitive than colour-contrast PT?
Fluorescent penetrant is generally the more sensitive choice for small imperfections, because the indication glows under UV-A against a dark background. ISO 23277 Annex A recommends, for acceptance level 1 on a fine surface, a fluorescent system of normal sensitivity or higher to ISO 3452-2, or a high-sensitivity colour-contrast system; at levels 2 and 3 any system can be used. Fluorescent inspection needs UV-A of 10 W/m² or more with no more than 20 lx of visible light, colour-contrast inspection 500 lx or more of white light (ISO 3059).
How does PT fit into ISO 3834 quality records?
Each PT report should reference the NDT procedure, the inspector and certification, the penetrant system and batch, the surface temperature, the actual penetration and development times, the viewing conditions measured, every recorded indication with its size and disposition, and the acceptance level applied. Under ISO 3834 and EN 1090 these reports are part of the weld quality records that auditors sample, so keep them traceable to the weld map.
Close the Loop Between PT Records and Your Weld Process Data
Therness thermal and visual weld monitoring systems log interpass temperatures and weld identities in real time — providing the process traceability backbone that makes PT reports audit-ready for ISO 3834 and EN 1090 CE marking without manual transcription.
Talk to a weld quality specialistTherness solution: Welding monitoring system — Every weld inspected in the cycle, with defect flags and the ISO 3834 / ISO 17635 evidence kept per weld.
Frequently Asked Questions
What is a PT test in welding?
PT in welding stands for penetrant testing, also called liquid penetrant or dye penetrant testing (LPT, DPT). A coloured or fluorescent liquid is applied to the clean weld and left to soak into imperfections open to the surface; the excess is removed and a developer draws the penetrant back out as a visible indication. PT finds only surface-breaking imperfections such as cracks, surface porosity and lack of fusion open to the surface, and it works on any non-porous metal, including austenitic stainless steel and aluminium, where magnetic particle testing cannot be used. The method is ISO 3452-1; acceptance of indications in welds is ISO 23277.
Which standards govern penetrant testing of welds?
ISO 3452-1 sets the general principles of the penetrant test: penetrant systems, process steps and the test report. ISO 3452-2 classifies penetrant materials and their sensitivity levels. Viewing conditions come from ISO 3059. ISO 23277 sets acceptance levels 1, 2 and 3 for indications in welds, and ISO 17635 relates them to the ISO 5817 and ISO 10042 quality levels. In North America ASTM E1417 is the penetrant testing practice; under ASME, Section V Article 6 covers the examination method and the construction code sets acceptance. Take each clause from the edition named in the contract.
What defects can penetrant testing detect in welds?
PT detects surface-breaking discontinuities: longitudinal and transverse cracks, toe cracks in the heat-affected zone (HAZ), root cracks where the root is accessible, crater cracks, lack of fusion open to the surface, surface porosity, and cold laps. It does not detect internal defects such as buried porosity, slag inclusions, or lack of fusion below the surface. For internal volumetric inspection, PAUT or RT is required.
What are the ISO 23277 acceptance levels for PT indications in welds?
ISO 23277:2015 Table 1 accepts linear indications (length more than three times the width) up to 2 mm at level 1, 4 mm at level 2 and 8 mm at level 3, and non-linear indications up to a major dimension of 4 mm, 6 mm and 8 mm. Levels 2 and 3 can carry the suffix X, which means every linear indication detected is assessed to level 1. The test surface is the weld metal plus 10 mm of parent metal on each side. Grouped indications are not covered.
What is a linear indication in penetrant testing?
Under ISO 23277 (3.1) a linear indication is one whose length is more than three times its width; any other indication is non-linear (3.2). Linear indications are judged by their length: up to 2 mm at level 1, 4 mm at level 2 and 8 mm at level 3. Indications roughly in line and separated by less than the length of the smaller one count as one continuous indication (5.1).
What is the dwell time for penetrant testing of welds?
ISO 23277 does not fix a dwell time. The penetration (dwell) time and the development time are set in the written procedure to ISO 3452-1, for the penetrant product and the surface temperature in use. ISO 23277 (5.2) requires the final sizing of each indication after the designated minimum development time and before the indication has spread so far that it no longer represents the imperfection. Cutting the dwell time to speed up inspection is a frequent cause of missed tight cracks.
Can penetrant testing be applied to austenitic stainless steel welds?
Yes. Unlike magnetic particle testing (MT), PT does not depend on magnetic permeability, so it applies to austenitic stainless steels (grades 304, 316, 321), aluminium alloys, nickel alloys, titanium and copper alloys. For stainless steel in process plant service, specifications often require low-halogen penetrant products, so the inspection consumables do not contaminate the surface.
Is fluorescent PT more sensitive than colour-contrast PT?
Fluorescent penetrant is generally the more sensitive choice for small imperfections, because the indication glows under UV-A against a dark background. ISO 23277 Annex A recommends, for acceptance level 1 on a fine surface, a fluorescent system of normal sensitivity or higher to ISO 3452-2, or a high-sensitivity colour-contrast system; at levels 2 and 3 any system can be used. Fluorescent inspection needs UV-A of 10 W/m² or more with no more than 20 lx of visible light, colour-contrast inspection 500 lx or more of white light (ISO 3059).
How does PT fit into ISO 3834 quality records?
Each PT report should reference the NDT procedure, the inspector and certification, the penetrant system and batch, the surface temperature, the actual penetration and development times, the viewing conditions measured, every recorded indication with its size and disposition, and the acceptance level applied. Under ISO 3834 and EN 1090 these reports are part of the weld quality records that auditors sample, so keep them traceable to the weld map.
