The main passivation standards are ASTM A967 (the current specification for chemical passivation of stainless steel), ASTM A380 (cleaning and descaling), and AMS 2700 (aerospace passivation, which superseded the old QQ-P-35). They define the passivation chemistry, process, and the tests used to prove the passive layer was restored.
The key passivation standards
| Standard | What it covers |
|---|---|
| ASTM A967 | Chemical passivation of stainless steel parts – nitric and citric methods, plus test methods |
| ASTM A380 | Cleaning, descaling, and passivation of stainless steel surfaces and systems |
| AMS 2700 | Aerospace passivation (Method 1 nitric, Method 2 citric) – superseded QQ-P-35 |
| QQ-P-35 | Legacy federal passivation spec, now largely replaced by ASTM A967 / AMS 2700 |
ASTM A380 is covered in depth on its own page: ASTM A380 — cleaning, descaling and passivation explained — including how A380 differs from A967, pickling versus passivation, the acceptance tests A380 defines, and the documentation an A380 scope should produce.
How passivation is verified
After passivation, the passive layer is confirmed with tests such as water-break, copper sulfate, ferroxyl (potassium ferricyanide), or high-humidity exposure – and documented. On regulated systems, that documentation is part of the turnover package.
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Frequently asked questions
What is ASTM A967?
ASTM A967 is the standard specification for chemical passivation treatments of stainless steel parts. It defines nitric and citric passivation processes, cleaning requirements, and acceptance tests for verifying that free iron has been removed and the passive film restored. Paul Industries passivates to A967.
What does ASTM A967 require for passivation?
It requires a clean surface free of oils and scale, a specified passivation treatment (nitric or citric with defined concentration, temperature, and time), thorough rinsing, and passing one or more acceptance tests confirming freedom from free iron and surface contaminants.
What acceptance tests are in ASTM A967?
A967 lists several acceptance practices and the specification is expected to name which one applies. Water immersion cycles the part between immersion and drying and looks for rust. The high humidity test holds it in a humid chamber for a defined period. Salt spray follows ASTM B117. The copper sulphate test deposits copper wherever free iron remains. The potassium ferricyanide nitric acid test, the ferroxyl test, develops blue colouration in the presence of iron and is the most sensitive of the set. Passing means the absence of a specified indication under defined conditions.
What is the difference between ASTM A967 and A380?
ASTM A967 covers passivation treatments and acceptance tests for parts; ASTM A380 covers cleaning, descaling, and passivation of equipment and systems, including in-situ procedures. They are complementary, and Paul Industries works to both depending on whether the work is parts or installed systems.
Does ASTM A967 specify citric or nitric?
Both. ASTM A967 defines nitric passivation treatment codes and citric passivation treatment codes, allowing either chemistry. The user or engineer selects the method and treatment code appropriate to the alloy and application; both are compliant when performed and tested correctly.
What are ASTM A967 treatment codes?
The standard organizes treatments into numbered families rather than leaving chemistry open. The nitric series covers several combinations of nitric acid concentration, bath temperature and immersion time, with some variants including sodium dichromate as an inhibitor for grades prone to flash attack. The citric series does the same for citric acid at its own concentration, temperature and dwell combinations. Electropolishing is addressed separately, as are alternative chemistries where their performance is demonstrated. Citing A967 without naming the treatment code leaves the controlling parameters undefined.
Do I need ASTM A967 passivation for cGMP equipment?
Not by name. Current good manufacturing practice under 21 CFR 211.65 requires that equipment surfaces contacting product not be reactive, additive or absorptive in a way that alters the product; it does not name a passivation standard. A967 is how that outcome is conventionally achieved and, more importantly, evidenced. In practice most pharmaceutical specifications call for it because it gives a defined treatment and a defined acceptance test, which is what an inspector can actually examine. Your own specification, not the regulation, is what makes it mandatory.
How do you document ASTM A967 compliance?
With parameters, not a declaration. A defensible record states the treatment code used, chemistry and concentration, solution temperature, contact time, the immersion or circulation method, rinse-to-target evidence expressed as a measured conductivity or dissolved iron value rather than elapsed minutes, and the acceptance practice applied with its observed result and criterion. For installed systems it must also state which welds and sections were covered, since a certificate that does not cover the final tie-ins is a finding waiting to happen.
Does ASTM A967 cover cleaning before passivation?
A967 requires the surface be clean and free of contaminants before passivation but points to ASTM A380 for detailed cleaning and descaling procedures. Grease, oil, and heavy scale must be removed first, since passivation acids do not remove organic soils.
Which acceptance test should I choose under ASTM A967?
It depends on the part and sensitivity. Copper sulfate and ferroxyl tests are fast free-iron indicators; high-humidity and water immersion are less aggressive; salt spray is more severe. Paul Industries selects a test appropriate to the alloy and application and documents the result.
Does ASTM A967 apply to welded assemblies?
Yes, and welded assemblies are where it matters most. Welding consumes chromium at the surface and leaves heat tint plus a chromium-depleted heat-affected zone beside the joint, which is precisely where localized corrosion initiates. Two distinct problems need separating, though: heat tint is an oxide scale removed by descaling under ASTM A380, and passivation chemistry alone will not clear heavy tint. A967 addresses the free iron and the depleted film. Testing a weld that still carries heavy heat tint will fail for a reason A967 cannot fix.
Is ASTM A967 the same as AMS 2700?
No, but they overlap. AMS 2700 is an aerospace passivation specification with its own methods and tests; ASTM A967 is broader and widely used across process industries. Some specs reference both. Paul Industries works to A967/A380 for cGMP process equipment.
Can ASTM A967 passivation be verified in the field?
Partly, and the limitation is practical rather than technical. The ferroxyl and copper sulphate tests can be applied to accessible surfaces in place, but both leave reagent residue that must be removed completely, which makes them awkward on product contact surfaces and rules them out in some systems. For installed pipework the more useful field evidence is borescope examination at defined locations compared against baseline photographs, plus analysis of rinse and circulating water for dissolved iron and conductivity. Coupons installed at fabrication allow proper laboratory testing later.
What happens if a part fails ASTM A967 testing?
It is re-treated and re-tested, not accepted with a deviation. A failure normally means free iron remains, and the cause is usually procedural or hydraulic rather than chemical: insufficient flow in branches so chemistry never contacted the surface, temperature reached at the pump but not at the far end, rinsing stopped on a clock rather than at a measured target, or contamination present beforehand that passivation was never going to remove, such as embedded grinding debris or heat tint. Investigate which before simply repeating the cycle.
Does ASTM A967 guarantee corrosion resistance forever?
No, and treating it as permanent is a common misunderstanding. A967 verifies the condition of the surface at the time of testing. The passive film is maintained by the service environment and degrades under conditions that attack it: sustained high temperature, chlorides, abrasive cleaning, cavitation, or a galvanic couple with a dissimilar metal. A hot Water for Injection loop commonly needs derouging every one to three years. The durable approach is annual borescope inspection against baseline photographs with dissolved iron trending, not reliance on a certificate.
Does Paul Industries passivate to ASTM A967 nationwide?
Yes, working nationwide from Kilmarnock, Virginia for both shop and in-situ passivation. We do not operate regional branches, so crews mobilize for planned work and dates are confirmed at quotation. For passivation that is rarely a constraint, since the work almost always has to be scheduled into a shutdown window and the chemistry, equipment and waste arrangements need lead time to organize. Where a facility needs a same-hour response, a contractor with local presence is the better call and we will say so.
What is ASTM A967 passivation?
It is the chemical removal of free iron from a stainless steel surface so that a protective chromium oxide film can form and enrich, performed to a specification that defines both the treatment and how the result is verified. Machining, forming, cutting, handling and welding all leave iron at the surface, and that iron corrodes readily and seeds further attack. The acid removes it while leaving chromium in place. The acid does not create the passive film; it removes what was preventing the film forming properly.
What is the difference between ASTM A967 and ASTM A380?
They do different jobs and a thorough specification cites both. A380 is a standard practice covering cleaning, descaling and passivation of stainless steel parts, equipment and systems, so it addresses the whole surface preparation sequence including removal of heat tint and scale, and it applies to installed systems as well as parts. A967 is a specification for the passivation treatment itself, defining numbered treatments and the acceptance tests that verify them. In short, A380 tells you how to get the surface clean; A967 defines the passivation and proves it worked.
What is AMS 2700?
AMS 2700 is the SAE aerospace specification for passivation of corrosion-resistant steels, and it is the aerospace and defense counterpart to A967 rather than a pharmaceutical standard. It defines passivation methods covering nitric acid and citric acid routes with their own numbered variants and acceptance testing. It appears in pharmaceutical work occasionally where a component supplier serves both industries and defaults to it. The two are not interchangeable in a specification: if your quality system expects A967, a certificate citing AMS 2700 will attract questions even where the surface is sound.
Do you provide a passivation certificate?
Yes, and the certificate carries parameters rather than an assertion. It states the treatment code, chemistry and concentration, solution temperature, contact time, the method used, rinse-to-target evidence as a measured value, and the acceptance test with its criterion and observed result. For installed systems it identifies explicitly which welds and sections are covered, which matters because the recurring audit finding on split-scope projects is a passivation certificate that predates the final tie-ins. We include dated borescope photography at handover as the baseline for future comparison.
Passivate to spec
Paul Industries is a single-source supplier, installer, and validator – one accountable partner from design through documented startup. Tell us about your project and we will scope it.