Guide
What does ASTM A380 require for pickling and passivation, and how is it different from ASTM A967?
ASTM A380 is the ASTM International standard practice for cleaning, descaling, pickling and passivating stainless steel parts, assemblies, equipment and installed systems. It explains how to get a stainless surface free of oil, scale, weld heat tint and iron contamination, while ASTM A967 is the narrower specification that defines the chemical passivation treatments for stainless parts and the qualitative tests used to confirm that passivation worked.
By Saola Manufacturing engineering team · Published · Updated
Drawings for welded and machined stainless parts often carry a note such as “pickle and passivate per ASTM A380” or “passivate per ASTM A967”, and the two are frequently treated as interchangeable. They are not. This guide is for design engineers and buyers who write or receive those notes. It works from the published scopes of ASTM A380/A380M-25 and ASTM A967/A967M-25, from the Euro Inox handbook on pickling and passivating, and from the Nickel Institute handbook on cleaning and descaling. It explains what each document does, when a part needs pickling rather than passivation alone, and how to word a callout that a finishing processor can follow and an inspector can check. Confirm the edition your contract cites before relying on any detail.
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What does ASTM A380 cover?
ASTM A380 covers the whole surface-preparation sequence for stainless steel: precleaning, descaling, pickling, cleaning, passivation and the tests used to judge cleanness. It is written as a practice that recommends methods and precautions, not as a product specification with one pass/fail result.
The current edition, ASTM A380/A380M-25, added the word “Pickling” to the title, which now reads Standard Practice for Cleaning, Descaling, Pickling, and Passivation of Stainless Steel Parts, Equipment, and Systems. Its scope is not limited to small parts: it takes in parts, assemblies, equipment and installed systems, although it excludes equipment that has already been in service and descaling done at the mill. The practice describes mechanical and chemical descaling, acid pickling, alkaline, solvent and acid cleaning, extra cleaning steps for especially critical applications and the protection of cleaned surfaces, together with precautions on design features that trap solution, on rinsing, on reuse of solutions, on safety and on disposal.
Two features of A380 matter most to a buyer. First, because it is a practice, which of its many procedures applies to a given job is a matter for agreement between purchaser and supplier; a bare “per ASTM A380” does not by itself fix the chemistry or the test. Second, it carries a set of cleanness tests, from visual inspection and the water-break test for organic films to the high-humidity, copper sulfate and ferroxyl tests for free iron. The 2017 edition also states that, unless otherwise specified, a requirement for passivation means the removal of exogenous iron and iron compounds from the surface by chemical dissolution, without significantly affecting the stainless steel itself.
How is ASTM A380 different from ASTM A967?
ASTM A380 tells a processor how to clean, descale, pickle and passivate stainless steel; ASTM A967 specifies the chemical passivation treatments for finished parts and the tests a lot must pass. A380 is the broad process guide, and A967 is the acceptance document for the passivation step only.
The practical consequence is that the two documents answer different questions on a drawing. A380 is where you look for how to remove weld heat tint, mill scale or embedded iron, and for how to clean a large weldment or an installed system that cannot go into a tank. ASTM A967/A967M-25 gives only brief recommendations on descaling and cleaning and points to A380 for the fuller treatment of those steps. Its substance is the passivation itself: nitric acid, citric acid and electrochemical treatments, seven qualitative test practices (A to G) for confirming the result, and a requirement that passivated parts look chemically clean, with no etching, pitting or frosting. Many specifications therefore cite both, with A380 governing the preparation and pickling and A967 governing the final passivation and its proof.
| Point | ASTM A380/A380M | ASTM A967/A967M |
|---|---|---|
| Document type | Standard practice (recommended methods and precautions) | Standard specification (treatments plus acceptance tests) |
| Applies to | Parts, assemblies, equipment and installed systems | Stainless steel parts |
| Descaling and pickling | Covered: mechanical and chemical descaling, acid pickling, removal of heat tint and scale | Brief recommendations only; refers to A380/A380M for detail |
| Cleaning of oil and soil | Covered in detail: alkaline, solvent, acid and precision cleaning | Parts must be clean before treatment; cleaning practices discussed more fully in A380/A380M |
| Passivation | Defined; treatments described as guidance | Nitric acid, citric acid, electrochemical and other chemical solution treatments |
| Verification | Cleanness tests: visual, water-break, high humidity, copper sulfate, ferroxyl and others | Practices A to G: water immersion, high humidity, salt spray, copper sulfate, potassium ferricyanide-nitric acid, damp cloth, boiling water |
| Who picks the procedure | Purchaser and supplier by agreement | Purchaser; where the order is silent, the processor may select the treatment (per the NASA summary) |
| Best use on a drawing | Pickling of welds and scale; cleaning of systems | Passivation and its test on machined or fabricated parts |
Is pickling the same as passivation?
No. Pickling dissolves a thin layer of the metal itself to remove scale, weld heat tint and the chromium-depleted layer under it, while passivation removes free iron and other contamination without removing base metal.
The Euro Inox handbook on pickling and passivating stainless steel draws the line clearly. In its terms, pickling takes a thin skin of metal off the part, typically in a nitric-hydrofluoric acid mixture, and is the route for clearing heat-tinted weld zones whose surface chromium has been lowered. Passivation, by contrast, normally forms on its own, an oxidizing acid only helps it along, and no metal is taken off. The handbook also warns that nitric acid by itself passivates but does not pickle effectively.
That distinction explains most field failures. A part that is passivated in nitric or citric acid but still shows straw or blue weld tint has had its free iron removed, but the damaged oxide and the depleted layer are still there, so the weld zone keeps its reduced corrosion resistance. Conversely, pickling a machined part that has no scale or heat tint removes metal for no benefit and risks etching fine finishes and threads. The process should match the surface condition, not the habit of the shop.
When does a stainless part need pickling rather than passivation alone?
A part needs pickling when it carries something that passivation cannot dissolve: visible weld heat tint, scale from hot working or heat treatment in air, or a chromium-depleted surface. A clean machined part from annealed bar, with no welding or heating after machining, usually needs passivation only.
Heat tint is the main trigger. As the Euro Inox handbook explains, chromium oxidizes more readily than iron, so the colored oxide draws chromium to the surface and leaves a layer just beneath it with less chromium than the bulk alloy; it calls removal of all visible heat tint good practice. The same reasoning applies to oxide scale formed during annealing, solution treating or hardening in an air furnace. Parts heat treated in vacuum or a protective atmosphere that come out bright normally need no descaling.
Pickling has its own risks, which is why A380 surrounds it with precautions. The Nickel Institute handbook on cleaning and descaling stainless steels gives 120 to 140 °F as the usual operating range for nitric/hydrofluoric baths, says that running below 120 °F slows intergranular attack on sensitized weld zones, and recommends using these baths on chromium-nickel grades only when the metal has no carbide precipitation and is ideally in the annealed condition. It treats straight-chromium (ferritic and martensitic) grades separately. For welded austenitic parts, choosing a low-carbon grade such as 304L or 316L reduces the sensitization that makes pickling attack worse.
| Part condition | What is on the surface | Treatment | Callout to put on the drawing or RFQ |
|---|---|---|---|
| Machined from annealed bar, no welding or heating | Oil, coolant, free iron from tools and handling | Degrease, then passivate | PASSIVATE PER ASTM A967/A967M-25; VERIFY PER PRACTICE [X], EACH LOT |
| Welded, visible heat tint at welds | Heat-tint oxide and chromium-depleted layer, plus free iron | Pickle welds and heat-affected zones, then passivate | PICKLE WELDS AND HAZ TO REMOVE ALL VISIBLE HEAT TINT PER ASTM A380/A380M-25, THEN PASSIVATE PER ASTM A967/A967M-25 |
| Heat treated in air, visible scale | Oxide scale over a depleted surface | Descale (mechanical or chemical) and pickle, then passivate | DESCALE AND PICKLE PER ASTM A380/A380M-25 AFTER HEAT TREATMENT, THEN PASSIVATE PER ASTM A967/A967M-25 |
| Vacuum or bright heat treated, no visible oxide | Light soil and free iron | Clean, then passivate | PASSIVATE PER ASTM A967/A967M-25 AFTER FINAL HEAT TREATMENT |
| Ground, brushed or blasted with tools or media used on carbon steel | Embedded iron particles, possible rust staining | Acid clean to remove embedded iron, then passivate and test for free iron | REMOVE EMBEDDED IRON PER ASTM A380/A380M-25; PASSIVATE AND TEST PER ASTM A967/A967M-25 |
| Large weldment or installed system that cannot be immersed | Heat tint at site welds, construction soil | Local pickling with paste, gel or spray, rinse, then passivate | CLEAN AND PICKLE IN PLACE PER ASTM A380/A380M-25; ACCEPTANCE BY AGREED CLEANNESS TEST |
Do you need to passivate after pickling?
A freshly pickled surface re-forms its passive film on its own in clean air, so a separate passivation bath is not chemically essential. Most drawings still call for passivation after pickling, because it removes iron picked up after pickling and gives a defined treatment that can be tested to ASTM A967.
The Euro Inox handbook notes that in nitric-based acid treatments pickling and passivation can occur in sequence, not simultaneously, and that passivation normally develops naturally on a clean surface. The reason buyers specify the second step anyway is control. A pickled weldment is often handled, fixtured, ground at a few spots or stored before shipment, and any contact with carbon steel can put free iron back on the surface. A final passivation treatment followed by a named A967 test turns “the surface should be clean” into a recorded result for the lot, which is what a receiving inspector and a certificate of conformance need.
Sequence matters as much as chemistry. Pickling and passivation come after the last welding, grinding, machining, deburring and marking operations; anything done afterward can reopen the problem. Oil and coolant must come off first, because acid cannot reach scale or iron under an organic film, and A380 offers the water-break test as a simple check that the surface is free of oil before treatment.
How should a drawing or RFQ call out ASTM A380 and ASTM A967?
Name what each document governs: cite ASTM A380 for the cleaning, descaling or pickling step and the surfaces it applies to, and cite ASTM A967 for the passivation treatment family, the test practice and how often it is run. Include the edition year of each document.
A note that says only “pickle and passivate per ASTM A380” leaves the chemistry, the extent and the acceptance test to the supplier, because A380 is a practice whose procedures are chosen by agreement. A stronger note states which surfaces are pickled (all surfaces, or welds and heat-affected zones only), that all visible heat tint must be removed, the passivation specification and treatment family, the A967 test practice and the sampling, and any surfaces that must be masked or must not be etched, such as precision bores, threads or sealing faces. For free-machining grades such as 303, add that the treatment must suit free-machining stainless, since some acid treatments can attack the sulfide inclusions in these grades.
Ask for a certificate that reports the specification and edition, the treatment actually used, the test practice and its result, the lot, and the name of the shop that ran the bath. When we review a stainless drawing for CNC turning or CNC milling, we check whether the part is welded, annealed or hardened after machining, because that decides whether the note needs an A380 pickling step or an A967 passivation step alone, and we confirm which finishing processor will run the treatment and issue the test record. Raise the callout with the drawing when you send it for a quote, so the route is settled before the first lot is made.
Frequently asked
What is the latest edition of ASTM A380?
The current edition is ASTM A380/A380M-25, published in 2025. It replaced the 2017 edition and adds “Pickling” to the title. Drawings that cite A380-17 or an earlier edition still refer to that edition unless the contract says the latest edition applies, so check the revision on the purchase order.
Is ASTM A380 mandatory or only guidance?
A380 is a standard practice, so its methods are recommendations, and which procedures apply is set by agreement between purchaser and supplier. It becomes binding to the extent a drawing or contract invokes it, which is why the callout should say which step and which surfaces it governs.
Does passivation remove weld heat tint?
No. Nitric and citric passivation treatments remove free iron but do not dissolve heat-tint oxide or the chromium-depleted layer beneath it. Heat tint is removed by pickling, by mechanical removal of the affected layer, or by electropolishing, followed by passivation if the drawing calls for it.
Is ASTM A967 the same as AMS 2700?
No. Both specify nitric and citric passivation of stainless steel, but SAE AMS 2700 is the aerospace specification, organized into methods, types and classes with a default when the order is silent, while ASTM A967 is the general industrial specification. Neither is a pickling specification; for pickling, ASTM A380 is the usual reference.
Does pickling change the dimensions of a machined part?
Pickling removes a thin layer of metal, so it can affect fine threads, sharp edges, close-fit bores and polished faces, especially on sensitized or free-machining material. Passivation removes no base metal. If a welded assembly has tight machined features, finish-machine them after pickling or mask them, and say so on the drawing.
Sources
- ASTM A380/A380M-25, Standard Practice for Cleaning, Descaling, Pickling, and Passivation of Stainless Steel Parts, Equipment, and Systems, ASTM International, 2025 (published scope), and the 2017 edition scope (meaning of passivation)
- ASTM A967/A967M-25, Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts, ASTM International, 2025 (published scope)
- Pickling and Passivating Stainless Steel, Euro Inox, Materials and Applications Series Volume 4, second edition, 2007
- Cleaning and Descaling Stainless Steels, Designers’ Handbook Series No 9001, American Iron and Steel Institute, distributed by the Nickel Institute, republished 2020
- Citric Acid Passivation of Stainless Steel, United Space Alliance and NASA Kennedy Space Center, conference presentation, 2011 (NTRS 20110001362) (summary of ASTM A967 and AMS 2700 requirements as they stood at the time)