Guide
AMS 2700 passivation or ASTM A967: which should your drawing call, and what proves it was done?
AMS 2700 passivation is the SAE aerospace specification for removing free iron and other less noble contaminants from corrosion-resistant steel parts, with controlled nitric (Method 1) or citric (Method 2) treatments and lot verification tests. Call AMS 2700 when the requirement flows down from an aerospace or space customer; for general industrial parts ASTM A967 is usually enough, as long as the note names the test practice and the certificate reports it.
By Saola Manufacturing engineering team · Published · Updated
The basics of what passivation does, nitric versus citric, and why free-machining grades need care are in the ASTM A967 passivation guide, and pickling is covered in the ASTM A380 guide. This page is about the two specifications side by side: what each one makes the processor do, which test proves the lot, and how the certificate should read.
On this page
What is AMS 2700, and which revision is current?
AMS 2700 is an SAE Aerospace Material Specification first issued in 2000; SAE lists AMS2700G, revised May 2025, as the current revision after AMS2700F of 2018. Cite the letter on the drawing, because methods, tests and ordering data have changed between revisions.
The scope in the SAE record is short: the specification covers the requirements for a process to assure removal of free iron or other less noble contaminants from the surfaces of corrosion resistant steel parts (SAE Mobilus record for AMS2700F, with revision history). Some drawings and process specifications still use the Roman-numeral type names of the older AMS-QQ-P-35; NASA's PRC-5002G says so in a note to its alloy table.
AMS 2700 is a paid document, so this guide does not quote its bath ranges or acceptance values. What can be read on open pages is how a large customer flows it down. NASA Johnson Space Center's process specification PRC-5002G, for example, requires all its corrosion-resistant steel passivation to follow AMS 2700 with local modifications, allows only Method 1 nitric acid, and requires all corrosion-resistance testing to meet Class 4 (NASA JSC PRC-5002G, 2021). That is a good picture of the norm: an aerospace buyer rarely calls bare AMS 2700, but adds a method, a type and a class.
How do AMS 2700 and ASTM A967 differ in practice?
Both specifications aim at the same clean, passive surface, but AMS 2700 is written for aerospace process control and flowdown, while ASTM A967 is a general industrial specification that leaves more of the choices to the purchaser. The table shows where the differences show up on an order.
ASTM A967/A967M-25 says in its scope that it defines several alternative chemical treatments, gives non-mandatory guidance on choosing one for a grade, and makes no recommendation about which grade, treatment or acceptance criteria suit a particular application (ASTM A967/A967M-25 scope). In other words, A967 gives you a menu, and the drawing has to choose from it.
| Point | SAE AMS 2700 | ASTM A967/A967M |
|---|---|---|
| Typical user | Aerospace and space primes and their supply chains | General industrial, medical device, food and fluid-handling parts |
| Treatment choice | Method 1 (nitric, several types) or Method 2 (citric) | Several nitric, citric and other treatments; purchaser or processor selects |
| Type names on drawings | Often QQ-P-35 Roman numerals, such as Type II or Type VI | Named treatments, such as Nitric 2 or Citric 2 |
| Verification tests | Lot tests detailed in AMS 2700, several citing AMS-STD-753 methods | Practices A to G (water immersion through boiling water) |
| Test selection | Set by class and by the customer flowdown | Purchaser names the practice; the spec does not pick one |
| Process control | Bath analysis and temperature records expected by flowdown documents | Bath control left largely to the processor |
| Where it fits | Parts whose drawing or contract already names it | Parts with no aerospace flowdown |
What do the methods and types mean on a drawing?
Method 1 is nitric acid and Method 2 is citric acid; the type inside Method 1 picks the nitric bath, with or without sodium dichromate. If the drawing names no type, the processor normally chooses one that suits the alloy.
PRC-5002G gives a plain example of the type language. Its Type II is a medium-temperature nitric acid solution with sodium dichromate, and its Type VI is a low-temperature nitric acid solution with no hexavalent chromium; NASA prefers Type VI where its alloy table allows it, and marks Types VII and VIII as not recommended for new design (PRC-5002G). The same document notes that martensitic and free-machining grades such as 416, 420 and 440C sit in different type columns from 304 and 316, which is the main reason a single bath is not right for every grade.
Two warnings in PRC-5002G apply to any order: do not passivate stainless parts with nitrided, carbonitrided or carburized surfaces, and do not descale or pickle before passivation unless the drawing says so. If your part is case-hardened or has been heat treated with scale, write the sequence on the drawing rather than leaving it to the finisher.
Which verification test should you name?
Name one lot test, and state how many parts it covers. For AMS 2700 work the common choices are water immersion, high humidity, salt spray or copper sulfate; for ASTM A967 work they are Practices A to G.
PRC-5002G lists the four AMS 2700 lot tests it accepts: water immersion per AMS-STD-753 Method 100, the high humidity test in AMS 2700, salt spray for a minimum of 2 hours per ASTM B117, and copper sulfate per AMS-STD-753 Method 102 (PRC-5002G section 8.1). ASTM A967 lists seven qualitative practices, from Practice A water immersion to Practice G boiling water immersion (ASTM A967/A967M-25).
Choose by part. Copper sulfate is quick and sensitive, but it plates copper onto any free iron it finds and marks the surface, so it is usually run on sample parts. Humidity and salt spray take cabinet time and are better as lot or qualification tests. Water immersion is simple and suits parts that tolerate wetting. Whatever you pick, put it in the drawing note; otherwise the processor picks, and the certificate may report a test you would not have chosen.
What should the drawing note say?
State the specification with its revision letter, the method, the type if it matters, the class or test practice, and the sampling. Those five items are what the processor and the inspector will read back to you on the certificate.
Generic wording to adapt, not any customer's standard:
PASSIVATE PER SAE AMS 2700 [REV], METHOD 1, TYPE [ ], CLASS [ ]. VERIFY EACH LOT PER [TEST]. NO ETCHING, PITTING OR FROSTING. — for parts that carry an aerospace flowdown.
PASSIVATE PER ASTM A967/A967M-25, NITRIC OR CITRIC AT PROCESSOR'S OPTION. VERIFY PER PRACTICE [ ], [SAMPLE SIZE] PER LOT. — for general industrial parts.
Do not write both specifications on one drawing “to be safe”. They have different test sets and class schemes, and a processor working to one cannot easily certify to both. If a customer needs AMS 2700, say so and accept the extra process control; if not, A967 with a named practice is clearer and is the more common industrial call.
What should the certificate and process records show?
The certificate of conformance should name the specification and revision, method and type used, the test run and its result, the lot and quantity, and the processor. For AMS 2700 work, ask that bath analysis and temperature records be available on request.
PRC-5002G requires the method used and the results to appear on the facility or vendor certificate of conformance, and it requires weekly analysis of the passivation solution against the AMS 2700 ranges and a bath temperature check before each use (PRC-5002G sections 6.2 and 8). Those are a reasonable model for what to ask any processor to keep, even under ASTM A967.
When machining and passivation happen at different companies, ask for the certificate to come from the shop that ran the bath, or to be backed by its record. Ask also how parts are handled and packed after passivation, since carbon-steel racks or bins can put free iron straight back on the surface. At receiving, a visual check for etching or frosting and a review of the certificate against the note are the practical acceptance steps; the certificate of conformance guide covers the general format.
How is passivation handled on a Saola order?
Passivation is not on the current finish menu, so raise any AMS 2700 or ASTM A967 callout at drawing review before quoting. The stainless grade on your drawing is also confirmed at that review.
The lead plant in Vietnam machines turned and milled parts on its CNC turning and CNC milling lines. Finishing is a managed process at partner plants, and the current menu on the surface finishing page lists eight finishes: electroplating, gold plating, zinc plating, RoHS blue trivalent chromate, oil-dip rust protection, anodizing on aluminum, powder coating and pad printing.
Because passivation is not one of them, a drawing with a passivation note gets reviewed for that step before any price is given, and the quote states where each step would be done. Stainless grades such as 303, 304 or 316 are not on the turning page's standard bar list, so the grade and its source are confirmed at the same review. Material certification is available on request, and the first-article and lot inspection records are described on the quality page. Send the drawing for a quote with the passivation note written the way you intend it.
Frequently asked
Can a part passivated to ASTM A967 be accepted against an AMS 2700 drawing?
Only if the customer agrees in writing. The tests and process controls differ, so a supplier deviation request is the right route, not a quiet substitution.
Is citric acid passivation allowed under AMS 2700?
Yes, as Method 2. Some customer flowdowns still restrict it; NASA JSC's PRC-5002G, for example, allows only Method 1 nitric acid on its hardware. Check your customer's flowdown before choosing.
What does a Class mean in AMS 2700?
The class ties the part to a level of verification testing. Class definitions sit in the paid specification and differ between summaries, so take them from the current revision your customer cites rather than from a secondary page.
Does passivation change part dimensions?
A correct treatment should not visibly change size or appearance, and both specifications treat etching, pitting or frosting as a defect. A frosted part, especially in a free-machining grade, means the bath or the grade selection was wrong.
Do I still need passivation on electropolished parts?
It depends on what the drawing and the customer flowdown accept. Electropolishing is a different process with its own specification, so do not assume one replaces the other; the electropolishing vs passivation guide compares the two.
Sources
- SAE AMS2700F, Passivation of Corrosion Resistant Steels (record with scope and revision history, listing AMS2700G of May 2025), SAE International, 2018
- ASTM A967/A967M-25, Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts (published scope), ASTM International, 2025
- PRC-5002G, Process Specification for Passivation and Pickling of Metallic Materials, NASA Lyndon B. Johnson Space Center, January 2021