Passivation Verification Tests: Which Verification, Which Documentation
Verification of passivation on 316L lines: test methods, acceptance criteria, and the content of the passivation compliance documentation.
No Single Test Proves Passivation
- No universal test: ASME BPE explicitly states that there is no generally accepted test that non-destructively proves on its own that a system has been passivated.
- Process documentation is primary: if a suitable chemical treatment was applied, the documentation generated during the process (written procedure, critical variable records, calibration and chemical certificates) provides assurance.
- Tests are complementary: visual inspection and free iron tests show cleanliness and surface iron, while electrochemical and surface analyses show quantitative passivation. Which tests are used is agreed upon in advance between the owner and the contractor.
For the passivation service itself, see our passivation and derouging page. In Mikron's service, verification tests such as Ferroxyl and water break are performed and reported.
Passivation and Cleanliness Tests: ASME BPE Table E-5-1
Test names and descriptions are based on the test matrix in ASME BPE-2019 Nonmandatory Appendix E and the referenced ASTM A380 and A967 practices. CT denotes cleanliness test, PT denotes passivation test, and RT denotes rouge presence test.
| Test | What it looks for and how it is performed | Quantitative? | Key considerations |
|---|---|---|---|
| 1. Gross inspection (ASTM A380 / A967, pass-fail) | |||
| Visual inspection (CT, RT) | Direct or remote (video endoscope, borescope) examination; cleanliness and presence of rouge | No | Interpretation is subjective; performed with minimal equipment |
| Wipe test (CT, RT) | Surface is wiped with a clean, lint-free white cloth or filter paper moistened with high-purity solvent | No | Useful on inaccessible surfaces; may leave fibers and may damage electropolished surfaces |
| Residual pattern test (CT) | Cleaned surface is dried; stains or water spots indicate contamination | No | Simple and fast; low sensitivity |
| Water break test (ASTM F22) (CT) | Surface is withdrawn vertically from an overflowing container of water; wetting pattern is evaluated | No | Detects hydrophobic contaminants such as oil and grease; not applicable to electropolished surfaces |
| Water wetting and drying (A380) / water immersion, Practice A (A967) (PT) | Immersion in distilled water or water washing followed by air drying. Modified version uses 3% to 7% salt water and DI-quality final rinse | No | Staining is evidence of free iron and potential pitting sites |
| High humidity test, Practice B (A967) (PT) | Coupon is treated with acetone or methyl alcohol, dried, and held at 97% humidity at 100 °F (approximately 38 °C) for 24 hours or longer | No | Benchtop only, with a coupon; not applicable to installed piping; time-consuming |
| Salt spray test, Practice C (A967) (PT) | 5% salt solution per ASTM B117 for at least 2 hours | No | Embedded free iron appears as rust or staining; evaluating film quality requires a longer test |
| 2. Precision inspection (ASTM A380 / A967, pass-fail) | |||
| Solvent ring test (CT) | A drop of high-purity solvent is agitated on the surface and evaporated on a quartz slide; organic contamination leaves a ring | No | A good test for organic contamination |
| Black light inspection (CT) | Ultraviolet light in the absence of white light; reveals certain oils and transparent films | No | Not practical for testing passivation |
| Atomizer test (ASTM F21) (CT) | Spray variation of the water break test, more sensitive to hydrophobic films | No | Requires direct visual inspection |
| Ferroxyl test, potassium ferricyanide and nitric acid, Practice E (A967) (PT) | Fresh solution is applied with an atomizer containing no iron or steel parts; a blue stain after 15 seconds indicates surface iron | No | Highly sensitive; detects only free iron, does not measure the passive layer; applied to non-system coupons, otherwise the test area must be cleaned per ASTM practice; false positives are easy |
| Copper sulfate test, Practice D (A967) (PT) | 250 cm³ solution: 1 cm³ sulfuric acid (specific gravity 1.84), 4 g copper sulfate, balance DI water. Swabbed onto a sacrificial coupon, keeping the surface wet for 6 minutes | No | Shows smeared iron well; small, discrete iron particles are difficult to detect |
| 3. Electrochemical field and benchtop tests | |||
| Cyclic polarization (similar to ASTM G61; G150 critical pitting temperature) | Critical pitting potential is measured; the more noble (positive), the more passive the surface | Yes | Requires a potentiostat and trained operator; benchtop test |
| Electrochemical pen (PT) | A pen with an electrolyte reservoir is placed on the surface; gives a result over an area of approximately 1.5 mm² against preset values | No, pass-fail | Used in the field; the measured area must be cleaned and repassivated after testing |
| Handheld corrosion potential kit (PT) | A moist pad and probe read the corrosion potential of the surface within seconds | Potential reading | Sensitive to user technique |
| 4. Surface chemical analysis | |||
| AES / Auger (PT, RT) | Surface composition from 2 Å to more than 100 Å depth using a primary electron beam | Yes | Ultra-high vacuum, conductive sample, limited instrument access, interpretation requires expertise |
| XPS / ESCA (PT, RT) | Elemental composition and chemical state of oxides at approximately 10 to 100 Å depth using X-rays | Yes | Ultra-high vacuum, limited instrument access, interpretation requires expertise |
| GD-OES (PT, RT) | Rapid quantitative depth profile of thin and thick film structures via controlled sputtering | Yes | Relatively high-cost, not widely accessible |
ASME BPE notes that all passivation-specific test results in ASTM A967 rely on visual detection of staining or discoloration, that these results are subjective and non-quantitative, yet may be sufficient in some applications. Electrochemical field tests and surface analyses are not part of the ASTM standards; they were developed to provide a more quantitative assessment.
What Is Acceptable?
Passivated surface (ASME BPE Table SF-2.6-1)
- Surface particulates: no particulates visible to the unaided eye under adequate room lighting without magnification.
- Staining: not acceptable; weld discoloration must comply with the relevant weld table.
- Construction debris: no visible residue is acceptable.
- Oils and organic matter: no visible trace is acceptable.
These apply in addition to the criteria in the surface finish tables (pits, scratches, roughness). Supplemental tests may be selected from Table E-5-1.
Process qualification coupons (Table E-3.2-1)
| Material | Method | Cr/Fe ratio | Oxide depth |
|---|---|---|---|
| 316 or 316L | AES | 1.0 or greater | at least 15 Å |
| 316 or 316L | GD-OES | 1.0 or greater | at least 15 Å |
| 316 or 316L | XPS/ESCA | 1.3 or greater | at least 15 Å |
Measured at the worst discoloration point in the weld zone and on the base metal. Because metal oxide readings are higher than metal readings, different methods are not expected to yield identical values. These ratios apply to coupons qualifying the procedure, not to the installed system in the field.
Passivation Documentation Package
Procedure qualification
- Process definition: preliminary survey, flushing, cleaning, passivation, final rinse, verification
- Critical variables: time, solution temperature, chemistry, endpoint determination, final rinse water conductivity
- ESCA/XPS or AES or GD-OES result for each qualification specimen
During execution
- Documentation showing that the written procedure was followed
- Record that the final rinse met the predetermined conductivity requirement
- Thorough rinsing with DI or owner-approved water following chemical treatment
Certificate of compliance
- Customer, system or component identification, firm, qualified method
- Written procedure, critical variable records, instrument calibration records
- Certificates of analysis for all chemicals used
- Process testing, verification, and post-passivation verification method
Final rinse conductivity can be monitored inline. Built for ultrapure water and water for injection lines, the Hamilton Conducell UPW conductivity sensor measures in the 0.01 to 1,500 µS/cm range; see our online analyzers page for detailed selection.
Inspection Conditions and Planning
How is visual inspection performed?
For direct visual inspection, ASME BPE specifies a light source with a color temperature between 5,000 and 6,500 K, an illumination of at least 500 lux at the surface, viewing with the eye at most 600 mm from the surface and at an angle of at least 30 degrees, and that the inspector meet vision requirements. In inaccessible areas, remote inspection is performed with a videoscope or borescope; its resolution must be equivalent to direct inspection, and the possibility that colors in the image may differ from true colors must be taken into account.
When and on which surfaces?
- Passivation is required after welding and fabrication and whenever a new component is welded into the system. The passivation requirement in the surface finish part of ASME BPE is limited to newly installed or newly modified portions.
- Passivation of electropolished surfaces is not required unless altered by welding, mechanical polishing, or external contamination.
- Heat tint is not removed by passivation; removing it requires an acid more aggressive than the nitric or citric acid used in passivation. Pickling does not replace passivation.
- Passivation cannot reverse the effect of improper argon purge; weld quality is inspected separately. Prepared for PW and WFI production systems, the ISO 22519 presentation specifies orbital welding wherever possible on product-contact piping, inspection of at least 70% of automatic welds and all manual welds, maintaining a weld log, and performing passivation during commissioning.
Installation inspection (including borescopy), IQ/OQ/PQ protocols, and preparation of the documentation package are carried out under system validation and qualification, while design and commissioning are handled under engineering solutions. For the sequence when rouge forms, see rouging and derouging; for surface roughness values, see hygienic design and dead legs.
Sources: ASME BPE-2019 (SF-2.3, SF-2.4, SF-2.6, Nonmandatory Appendix E Tables E-3.2-1, E-3.2-2, E-5-1; E-4.1, E-4.2); ASTM A380 and A967 practices as referenced via ASME BPE; ISO 22519 presentation.
Frequently Asked Questions About Passivation Verification Tests
Ferroxyl, water break, XPS/ESCA, acceptance criteria, and documentation.
How do you know passivation was successful?
ASME BPE states that there is no universally accepted non-destructive test that proves the presence of a passive layer on its own. Verification is therefore two-fold: process documentation showing that a qualified procedure was followed, and tests agreed upon between the owner and the contractor (visual inspection, free iron tests, and electrochemical or surface analysis if required).
Does the Ferroxyl test measure passivation?
No. The Ferroxyl test (potassium ferricyanide and nitric acid solution) detects free iron on the surface; a blue stain after 15 seconds is evidence of surface iron. It does not directly measure the quality of the passive oxide layer. It is highly sensitive and prone to false positives; the standard states that the test should be applied to non-system coupons, or else the tested area must be cleaned according to the ASTM practice.
Is the water break test a passivation test?
No, it is a cleanliness test. In the water break test, the surface is withdrawn vertically from water and the wetting pattern is observed; hydrophobic contaminants such as oil and grease are detected. ASME BPE also notes that the test is not applicable to all surfaces, including electropolished surfaces.
What are XPS/ESCA and the Cr/Fe ratio?
XPS (ESCA) is a surface analysis that quantitatively measures the elemental composition of the uppermost surface layers and which oxides are present; the chromium-to-iron (Cr/Fe) ratio is a measure indicating the degree of passivation. For process qualification coupons, ASME BPE gives 1.0 or greater by AES and GD-OES, 1.3 or greater by XPS/ESCA, and an oxide depth of at least 15 Å as minimum surface requirements. Because the analysis requires ultra-high vacuum and a coupon, it is used in procedure development rather than in the field.
What should be included in a passivation certificate of compliance?
According to ASME BPE, the customer name, system or component identification, firm performing the passivation, qualified method used, process documentation (written procedure, control records of critical variables, instrument calibration records, certificates of analysis for all chemicals used, process testing and verification), and the post-passivation verification method must be included in the certificate.
Why is final rinse water monitored?
After chemical treatment, the surface is rinsed with deionized or owner-approved water. Continuing the rinse until ionic contaminants, process chemicals, and by-products are removed, and determining this by conductivity analysis, is cited as good practice. The conductivity of the final rinse water is listed in the standard among the critical variables of passivation and must meet a predetermined quality requirement.
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