Letter 26009

Does my vendor's COLD passivation process for 300 series stainless steel meet the specs?  

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Is there a cold process for satisfying the requirements of QQ-P-35C [link is to spec at TechStreet] Type VII or does the process have to be accomplished with a warm to medium nitric acid bath. Currently a subcontractor that is finishing parts for my company is maintaining that a cold bath, with extended soak time, satisfies the requirements of QQ-P-35C. (I am aware that the spec is now ASTM A967 [link is to spec at TechStreet] )

I would appreciate a reply at the earliest....

JAMES SARLES
Ordnance Engineering - BRENTWOOD, TN, USA

James, if you take a Type VII bath (Nitric 3 in ASTM nomenclature) and use it at room temperature (70-90 F), you have a Type VI bath (Nitric 2). Unless your print calls out the bath, I'd guess you're OK to do that: they're used on similar alloys. The time is 30 minutes minimum rather than 20.

You know, if you take the opinion that QQ-P-35 was replaced by ASTM A 967, then in paragraph 6.1.1.5 of the ASTM it allows "Other combinations of temperature, time, and concentration of nitric acid, with or without other chemicals, including accelerants, inhibitors, or proprietary solutions, capable of producing parts that pass the specified test requirement." The specsmanship hassles come should you have to go the "QQ-P-35 becoming AMS-QQ-P-35 which will eventually be superseded by AMS-2700 [link is to spec at TechStreet]B" route.

Lee Gearhart metallurgist East Aurora, NY

REF AMS-QQ-P-35C AND/OR CURRENT SPECS FOR PASSIVATION;
DO ANY OF THE PASSIVATION SPECIFICATIONS ACTUALLY REQUIRE TESTING SUCH AS HIGH HUMIDITY? (TYPE II, VI, VII, VIII) MIL-F-14072 E300 - DOES THIS DIFFER FROM OTHER PASSIVATION SPECIFICATIONS? IS TESTING A REQUIREMENT?

THIS IS A GREY AREA FOR ME. I AM NOT WILLING TO PURCHASE ALL OF THE RELATIVE SPECS AS WE USE OUTSIDE VENDORS FOR ALL APPLIED FINISHES. I AM MOSTLY CURIOUS ABOUT THE ADDED COST FOR TESTING THAT I AM NOT CERTAIN IS A REQUIREMENT.

RICHARD GOULDMAN
JOB SHOP MACHINING - RICHMOND, VA, USA

AMS-QQ-P-35 has been superseded by AMS-2700C. The standard lists Method 1 Type 6 as "Low Temperature Nitric Acid". Basically, this is 20%-45% HNO3 with 30 minutes minimum immersion time at 70F-90F. The Method 1 Type 7 is considered "Medium Temperature Nitric Acid". This type is 20%-25% HNO3 with 20 minutes minimum immersion time at 120F-140F.

The AMS-2700C states that three types of testing for corrosion resistance verification are acceptable. They are:

Humidity - 95% Min. relative humidity at 100-115F for not less than 24hours. No red rust.

Copper Sulfate Test

Salt Spray - 2 hours exposure in salt spay environment in accordance to ASTM B 117. No red rust.

Our company used the Salt Spray for our PPAP testing. It only cost us 50 dollars for a minimum run charge since the time is so low.

Clay O'Shell
- Tyrone, PA, USA

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