Equivalent to QQ-P-35 spec for passivation of stainless steel? ASTM A967?

A. Dear Pam,

Unless you would like to possibly destroy parts you must investigate the ASTM spec. Look at finishing.com's FAQ on passivation of stainless steel and you will learn from the experts in the field...suffice to say that I saved myself a lot of grief by going with the ASTM spec.

I don't know if you are a job shop, or a captive shop, and as you will see from the write-ins on the FAQ...it makes a lot of difference. I don't know where your alloys are purchased from, and that makes a huge difference too. Please pay particular attention to the section on tooling changes (frequency) and how they can affect the surface composition of the alloy, and the necessity for sufficient cleaning time (up to 40-60 minutes) to remove all possible oil contamination from your parts. The very characteristics that make for free-machining stainless alloys (is it 416se?) also tends to trap oils. If you have the opportunity to extend your "process improvement technology a.k.a. Deming" to your supplier, or to the manufacturing side of your operation, you may be able to minimize the possible negative effects of overheating due to infrequent tooling changes. Selecting the best possible lubricating solution (that won't impregnate itself into the alloying constituents of your alloy) will help. Ensuring that what you bought (in terms of alloy) is what you really got, is also important. If I were you, I would do some very rigorous multiple-factor variance analysis coupled with copper indicator solution tests, as well as appropriate salt spray and other testing (re: appropriate ASTM specs).

Going from nitric to either citric-based or phosphoric acid solutions would be real advantageous. In fact, if your parts are expensive, investigate electropolishing in phosphoric acid solution. I spoke to ASTM people who were responsible for drafting the spec. Though they wouldn't directly admit it, (or accept any liability for it) they were in effect saying that the reason they drafted the spec. was to encourage and in effect justify what medical equipment and other manufacturers had effectively discovered for themselves: nitric is way too dicey, QC of stainless alloys too problematic, and consistent QA of machining processes (re: bit changes and lubrication) not possible in the job-shop world. Again, I refer you to the excellent compilation of passivation problems covered by finishing.com's FAQ on the subject at their web-site. Good luck, and here's hoping you can get the nitric out of your shop!

A. Victor:

QQ-P-35C has been cancelled in favor of ASTM A967 except for aerospace use. For aerospace you must use the AMS specifications AMSQQP35 [canceled] (nitric only) or AMS2700 (nitric or citric).

Many aerospace customers have tested the proprietary citric acid formulations and found them to be better than nitric, so they are switching over. Hopefully we will only have the AMSQQP35 [canceled]C canceled soon, also.

Let us know if you need details.

A. ASTM A967 is listed as the replacement for QQ-P-35 Rev. C, so I would think it would be for all cases.

A. QQ-P35C states Type IV solution has been withdrawn; see Table II for guidance. For 303 SS, Table II specifies Type II passivation solution (warm nitric acid + sodium dichromate). This solution is available in both QQ-P-35C (canceled) [link is to free spec at Defense Logistics Agency, dla.mil] and ASTM A967. The passivation of 303 SS can be problematic (pitting/frosting and early rusting), and a lengthier A-A-A (alkaline-acid-alkaline) procedure has been recommended since at least 1973. See letters 20840, 17774 and 639 as well as the FAQ: Problems with Passivation of Stainless Steel. AISI 303 is merely a composition. The passivation properties and corrosion resistance of 303 SS are greatly affected by the distribution and morphology of the MnS inclusions. Stringers are far worse than nodules. For salt spray requirements, I suggest using SS from well-known suppliers experienced in controlling these inclusions, such as Carpenter Technologies, Colt Industries, Jones & Laughlin, US Steel, BHP (Australia), British Steel, Dominion Foundries and Steel, Kawasaki Steel, Nippon Kokan, Sandvik AB, or Ugine Aciers. These companies published research results in the book Sulfide Inclusions in Steel (1975), and are not necessarily current SS producers.

A. Armando,

AMS2700 (which will eventually replace a to-be-cancelled AMSQQP35 [canceled]) does have the olde type IV listed.

A. Chris:

Not all stainless steel springs are passivated by the manufacturers, although it certainly would be advised if it is going into any kind of humid or corrosive atmosphere. We supply formulations to many of the spring manufacturers around the world for this purpose.

QQ-P-35C has been canceled in favor of ASTM A967 for all passivation except aerospace, which should use AMS2700. The passivation specification for nitric in ASTM A967 is IDENTICAL to the now defunct QQ-P spec. In addition it allows the improved passivation using citric formulations. There is no longer the need to passivate using the hazardous nitric systems, although passivation with nitric acid is certainly acceptable.

A. If you cannot use sodium dichromate you cannot use Type II, you must use Type VI or another Type depending on the alloy.

adv.
If you cannot successfully use Type VI you can contact us with more information and we can tell you how to do it.

A. RoHS is concerned with what is on the part, not what chemicals the part may have been exposed to during its processing, Mohammed. I don't suspect that there will be sodium dichromate compounds on the parts you ship, although I hope to be corrected if someone believes otherwise. Good luck.

A. You're asking the wrong questions. The technical differences are slight and shouldn't affect 304 SS:

QQ-P-35C, Type VI: 25-45 vol% nitric acid for 30 minutes at 70-90 °F.
ASTM A967, Nitric 2: 20-45 vol% nitric acid for 30 minutes (minimum) at 70-90 °F.

Black residue could be carbide or machining residue, heat treat or weld scale inadequately removed, residual machining lubricant that reacted with the nitric, or some unusual contamination in the passivation solution.
Verify that the material is 304, not a higher carbon alloy.
Check the entire machining, cleaning and passivation process.

A. Yes, much of A967 is copied fairly directly from QQP-35C. The major change was the addition of citric acid based passivation as an alternative to the nitric and nitric/dichromate.

Hi Sanjeev.

My read of cancelled QQ-P-35 is that if your customer is the American military/DoD, you might be able to automatically use ASTM A967, except for aerospace parts which must be done to AMS2700; but if the parts are destined elsewhere you must get spec replacement orders from your customer.

Regards,

A. Wow, QQ-P-35 Revision B! That's impressive. Revision C was released in 1988, and then QQ-P-35 was canceled ten years later as Ted mentioned. Your customer is over 25 years out of date! Revision B is so old, the US government's "ASSIST" mil spec site doesn't even have a copy.

Just to review various things:
The Type I and Type IV baths in fact were removed in revision C, which had only Type II, VI, VII, and VIII. The ASTM replacement for QQ-P-35, A967, renumbers these to Nitric 1, 2, 3, and 4. SAE's replacement for QQ-P-35, AMS2700, brought back all the removed baths and lists them as Method 1, Type 1-8.

ASTM A967 also has a Citric section, and AMS 2700 has citric as Method 2.

Officially, only DoD users are compelled to the automatic rollover from QQ-P-35 to the two newer standards. Everybody else ought to anyway, though. It's not as though there's a substantial difference, the new standards were specifically designed to keep the text of QQ-P-35 largely intact.

Q. Hello,

Thanks for your response.
I have another query regarding, whether QQ-P-35 Type- 1,2,3,_,_,_,_,8 are equivalent to AMS 2700E Type- 1,2,3,_,_,_,_,8 ?

Ex: If customer specifies QQ-P-35, Type-I, Can we consider the process according to AMS 2700E, Type-I?

Please advice.

Regards,

A. Hi Sanjeev. Yes, Ray implies that that is the case. However, you cannot substitute one spec for another except with your customer's approval. And don't even think about claiming to be plating to a spec unless a copy of that spec is in your hands :-)

Regards,