Acceptance criteria after salt spray test

A. Hi Yunus,

I would reject the part, the 650 mm^2 you select should be a large continuous surface (in this case it's a big plate). The corrosion pit is larger than the standard and you should reject. The bigger the pit the sooner it started corroding or the plating / supplemental coating was not thick enough to inhibit the corrosion that you're looking for.

Cheers.

A. Hi Steven. I assume these steel panels are painted or powder coated rather than galvanized? Hopefully a reader with architectural experience will understand your question better than I do, because I'm not "getting" this idea of an "aluminum interior". I don't think there is any possibility of a panel which is painted on one side but aluminum on the other passing a salt spray test which exposes both sides.

My reason for asking about the paint or powder coating is that the specifications for the coating, rather than the standards for how to conduct a salt spray test, is usually where to find the pass/fail criteria. So I don't think anyone can direct you to that pass/fail info until you describe the coating specification. Good luck.

Regards,

A. Hi Steven!

Maybe ISO 4628-3 (Paints and varnishes -- Evaluation of degradation of coatings: Assessment of degree of rusting) or ISO 4628-8 (Paints and varnishes -- Evaluation of degradation of coatings: Assessment of degree of delamination and corrosion around a scribe) can give you a reference to agree with your client the "fail" test.

You must always make an agreement with your client beforehand so you don't have problems in the future. I participated in many part developments (we make fasteners but I think it applies for everything) and when we had some problems with corrosion tests, it was about how the "fail" was assessed.

I think ASTM D610 (Standard Test Method for Evaluating Degree of Rusting on Painted Steel Surfaces) can help, too. In ISO 4628-3 there is a correlation chart so you won't need to get both standards for this one.

Best of luck and hope you solve this one!

? Hi Kyle. I think we need to clearly understand what the substrate and finishing process are. Are we understanding these are stainless steel parts which have been passivated? Knowing the grade of stainless steel would be helpful.

Regards,

A. Hi Sri. You tried to post this under the subject of "Salt Spray Test -- ASTM B117 Operational Problems", but we moved your question here because ASTM B117 tells you how to operate the test cabinet, but it does not tell you what constitutes failure of tested parts. You find out what constitutes failure in the specification that you are processing to. That can be totally different for aluminum parts, stainless parts, steel parts plated with different materials, steel parts phosphatized or black oxided, steel parts powder coated, etc.

It is not your job to build pass/fail rules, but to find out where that "140 hours" requirement came from, read the spec that dictated that 140 hours, and determine whether the parts complied with the testing requirements for that processing specification.

I am not saying that the spec will be 100% free of ambiguity. You may well come back to us and say that you are still not sure whether the parts passed or failed … but we can't talk about it until we know what spec you are trying to comply with and what it says about the subject. Good luck!

Regards,

A. Hi Sandeep. Please tell us who you are and what you do (plating shop employee, salt spray test lab, buyer, designer) and why you want to know. Then we'll have a starting point towards understanding your questions in a more useful way.

May we assume the bolts are steel? You can't apply yellow dichromate to steel, but you can apply it on top of cadmium plating, zinc plating, zinc alloy, and tin-zinc plating. So we have to assume that those bolts are plated. And all of those platings can generate white rust. So if your question was understood, the answer is yes, if those bolts corrode, it is possible for them to get white rust. Good luck.

Regards,

A. The only thing I can contribute is Cd or Ni plated bolts last a lot longer in salt spray when chromate coated. This is based on actual testing experience. Never had them in the chamber long enough to see a failure.

A. Hi Shilsagar. Please share who you are, what you do, and why you want to know, then people will probably be able to help you better :-)

Pending a response, 192 hours salt spray should be a safe specification.

The world largely shifted from hexavalent chromating to trivalent over the last few decades, and most trivalent chromates cannot match the corrosion resistance performance of the hexavalent chromates without an additional top coat, which may be a titanium, zirconium, or similar final dip which helps seal the surface away from the environment. Good luck.

Regards,

A. Hi Vinodh. First things first, how do you intend to paint these structurals? Will you be blasting the steel to "Commercial" standard NACE No.3, SSPC-SP-6, Swedish Sa-2? Or to what standard will you be blasting? Then what: galvanizing, phosphatizing, e-coating, and finally painting or just painting?

A good starting point is probably ⇨
From this you should be able to specify what kind of coating system you are looking for, and after you have selected it, you can try to determine how to test compliance with your spec. Good luck.

Regards,

A. Hi Isvaran. One sample part may not be enough to tell you much; you may need to repeat it a few times. But note that ASTM B117 tells you how to build and operate a salt fog cabinet, but it doesn't tell you what constitutes passing vs. failing. So, before you get into long discussions about how one sample can pass according to one testing house and another sample fail according to a different testing house, I think the first thing you need to do is to agree on exactly what constitutes passing vs. failure (rather than leaving it vague and subjective).

If you can't find a good recognized spec that covers trivalent chromate conversion coating of diecastings, there are several that cover chromate conversion coating of aluminum, and you could probably see how they define passing & failure and incorporate something similar into your spec. Good luck.

Regards,

A. Years ago I was employed at a testing lab. Salt spray testing was a speciality.

ASTM has illustrations of the two main criteria that could constitute failure, creepage and/or blistering. Creepage is measured on edges or a scribe in mm. Blisters are rated on size and density. The illustration uses a scale from 2 to 10 indicating the size of the blisters, and such as few-to-dense to indicate density.

Your customer needs to inform you of their requirements in these terms.

Unfortunately I no longer have access to the ASTM specifications, ASTM B117 should point you in the right direction.

  Thank you so much !
I'll try getting better specifications from the customer in the future.
This basically caused me to panic and assume I have messed up big time.
I really appreciate the quick assistance.

A. Hi Anup. On one level, that's an easy one: The root cause of it failing in the salt spray test is that it's not plated and chromated properly :-)

But the issue of exactly in what way and why it is not plated and chromated properly is, of course, far more complicated. What specification is it supposed to be plated in accordance with? Is it rusting solely within the threaded area or everywhere?

Regards,

A. Hi Majesh. More words please! Sorry, but I don't now what you mean by "how to handle".

What has your customer told you to do? If no one has told you to do anything, what would you like to learn from a salt spray test? Does your shop operate a salt spray chamber or would you send the parts out. What are you plating, and what specification are you plating to? Thanks.

Luck & Regards,

A. Hi Sandip. Well, that's the main function of salt spray testing: to tell you that you are not finishing the product the way you should :-)

Unfortunately I am not quite understanding your situation. Are you saying that you painted a 100 x 150 test panel and it survived 500 hours, then you painted your actual product and it survived only 48 hours? You are calling this actual product a 'casting sample hub' -- does 'casting' mean that it's cast iron or sintered metal?

Please describe exactly what the component is, what general technology was used to manufacture it, and what cleaning and pretreatment preceded the painting. Failure probably has a lot more to do with pretreatment than with paint thickness. Thanks.

Luck & Regards,

A. Hi Prakash.
ASTM B117, "Standard Practice for Operating Salt Spray (Fog) Apparatus", does not define the acceptance value ... only how to run the tests.

The components are presumably plated, painted, or otherwise finished according to some specification, and it is that specification which contains the acceptance criteria for compliance with the specification.
Luck & Regards,


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

A. Hi Anupam,
Black stain in 24 hours may not be a problem: please see posting by Subramanian Ramajayam on this page. The spec you have agreed to plate to tells you and your customer what constitutes satisfactory plating vs. failure. If you are not plating to any specification at all, there is no good way to agree upon whether the plating is satisfactory or it isn't; but you could still look at specs like ASTM B633 to see what they say about it.
Luck & Regards,


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

A. Hi Kamlesh.
Are you agreeing to apply lacquer in accord with any particular standard? If not, then waiting for a 48-hour cure time sounds fine to me, especially if your objective is simply to pass the test rather than to use it as an early warning of the process getting out of control.
Luck & Regards,


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