Need justification to eliminate salt spray testing of 300 stainless parts 2

[Screwman1]

I have a customer who makes marine accessories and uses a number of 304 stainless steel screws. They call out a 500 hour salt spray test for these screws. We get random salt spray failures even after passivation. I am trying to get the customer engineers to understand that this is not a valid test for these screws. Does anyone know of a document or source that specifically states that the B117 test should not be used for stainless steel parts?
By the way; I have tried to get them to change to 316L and they won't consider it because of the "prohibitive" cost.
I am almost to the point of recommending that we tell them that we will no longer supply these parts because of this salt spray test that they are putting the parts through.

 

[israelkk]

The old Federal Spec "QQ-P-35 PASSIVATION TREATMENTS FOR CORROSION-RESISTANT STEEL" is available at

http://everyspec.com/FED_SPECS/Q/QQ-P-35C_2385/

.It asks for only 2 hours. The NEW one AMS 2700E asks for 2 hours too. You can search them it google and you may find it too. The 500 hours request for passivation has no basis. Ask the customer for the spec he got the 500 hours.

 

[Screwman1]

Thanks KK,
That is the kind of info that I was looking for. I knew that I had seen the 2 hour requirement that is in QQ-P-35, but I couldn't for the life of me remember where it came from.
As far as I know, there is no actual scientific basis for the spec, it is something that someone at the customer "developed". This organization also tried to tell us that they had developed an "accelerated" test method that could determine if parts would pass the 500 hour test. The accelerated method consisted of wrapping copper wire around the parts to be tested, putting them into the SS chamber and then running current through the wire! When asked what the specification was for this, they were dumbfounded that we would ask such a thing.

 

[monkeydog]

I assume you are charging for the 500 hour salt spray test.
Charge accordingly for time, equipment etc. You need to make a profit on the 500 hour testing also.
If you are making a profit when you ship the parts, why fight it?

 

[EdStainless]

What is this guy making? I want to make sure that I never buy one.
304 will not stand up to seawater, even just spray.
And in a fastener application where there are tight crevices 316 will not survive long either.
316 only works in marine hardware where it can be washed off with fresh water regularly.

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P.E. Metallurgy, Plymouth Tube

 

[Screwman1]

Monkey,
They are conducting the test in-house on received parts. All we are getting out of it is returns on parts that are failing their test.

Ed,
These are lightly loaded AB tapping screws that are holding auxiliary electronics in the cockpit area. If it was any type of structural components I would be running too.

 

[btrueblood]

So they are pre-corroding the screws so the customer doesn't have to wait for the "patina" to form? Yeesh.

 

[mrfailure]

The salt spray test method in AMS 2700 "is used to detect anodic surface contamination, including free iron, on corrosion resistant steel" for a minimum of 2 hours. This seems to be a different purpose than salt spray testing for overall corrosion attack for a certain time of exposure as is required, which would be a customer requirement. Am I incorrect in interpreting that the 2-hour requirement is not germane for this purpose?

 

[weldstan]

The longest salt spray test that I have encountered was 5 hrs. The 2 hr test is most common. Never have seen a 500 hr test.

 

[mrfailure]

Stan,

The 5 hour maximum test makes sense if you are looking for anodic surface contamination. However, it is insufficient for general corrosion identification from exposure. That is a customer-specified property. In recent memory, our lab has conducted such testing for 300-series coupons for up to 200 hours of exposure.

 

[EdStainless]

By requiring 500 hours they are not looking for surface contamination, they are trying to find 304 that is marginally more corrosion resistant than general.

There are actually much more sensitive tests for Fe contamination.
My favorite is to use white Head and Shoulders shampoo. The active ingredient will complex with Fe and turn blue.
A thin layer of H&S, misting with DI water to keep damp, and a few hours. The most sensitive test that I have ever used.


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P.E. Metallurgy, Plymouth Tube

 

[monkeydog]

Seems like the best way to approach this is to certify to MS 2700E asks for 2 hours, anything tested in excess of that is on their nickle. Subcontracts folks have better words for what I am trying to say.