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Salt Spray Test for Powder Coated Fasteners

May 22, 2011

I am asked to perform SST on the incoming screws we purchased. Both screws are black oxided.
Based on the screw material, what is the salt spray test standard to follow and how many hour do we need to test.

1. Alloy Steel
2. Mild Steel

Husri Hussain
QA - Penang, Malaysia

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Hi, Husri.

Generally the purchaser establishes what criteria the finish should be tested to. But black oxide is not powder coating, so it seems that there is some confusion. So I think the first step is to gather the specifications to which the fasteners were supposed to be processed from your designers, and the certifications that they were processed to that specification from the plating/coating shop before we can even suggest what standards to look at.

As has been said here in other threads, putting the salt spray hours first is putting the horse before the cart because parts are not exposed to salt fog in real life. What needs to be done is to establish your real life requirement, and then see if salt spray hours can be helpful as any sort of gauge that you will achieve that desired life. Black oxide offers almost zero corrosion resistance, so the value of salt spray testing is doubly called into question. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 24, 2011

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Thanks for the feedback. its my mistake on the powder coating. It's black oxide screw that we are ordering on the two different type of base material.If the black oxide is non corrosion resistance , I would agree with you that the SST may not be the right test to determine the corrosive resistance ability on these black oxide parts. Hence, what will be the test that one could do/perform to determine the level of the corrosive resistance that the black oxide can sustain.
Thanks.

H.Hussain
- Penang, Malaysia
June 8, 2011

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August 9, 2011

Its really a waste of time testing black oxide finished parts. They will give probably between 1 and 8 hours if your lucky.
OK for internal use, any time outside and they will rust.

Barry

Barry Sloman
- Kilsyth Victoria Australia