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topic 35573p.3

Acceptance criteria after salt spray test

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A discussion started in 2005 but continuing through 2020

February 23, 2018

Q. Hi, how are you.
We are producing mortise locks. We are using EN 1670 [link by ed. to English BS EN 1670 spec at TechStreet] for salt spray test results. So I want to know about rust. It says that there cannot be any spots larger than 1,5 mm in 650 mm2.
I don't know how to interpret that because which 650 mm2 area will I choose. I mean if there is a big plate and there is just one spot with 2 mm, what should I say. It is ok or not?
Thank you so much

yunus sezgin [returning]
kalekilit - istanbul TURKEY

February 27, 2018

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.


Erick Leong
Vapor Bus International - Buffalo Grove, Illinois

March 16, 2018

Q. Hi, my name is Steven Sze. I'm an aluminium panel design engineer. The panels are mostly used for building cladding. Our company is about to have one of our steel panels tested (aluminium interior) against Salt Spray Test 1000 hours. May I know if there is any standard that we can refer to, to define if our product "Passed the test" or "Failed the test"?

Steven Sze
- Brisbane, Queensland, Australia

March 2018

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.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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March 19, 2018

A. Hi Steven!

Maybe ISO 4628-3 [affil. link to spec at Techstreet] (Paints and varnishes -- Evaluation of degradation of coatings: Assessment of degree of rusting) or ISO 4628-8 [affil. link to spec at Techstreet] (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 [affil. link to spec at Techstreet] (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!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

March 15, 2018

Q. We are following ASTM B 117 and NADCAP regulations on our chamber and I occasionally have parts that get a brown stain that I have failed previously as rust. However, on my most recent test pieces, I submersed them in Copper Sulfate to plate them and they did NOT turn pink. We abrasive blast with aluminum oxide prior to passivation. Any ideas on what my brown stains are?


Kyle Major
- Boss, Missouri, United States

March 2018

? 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.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

March 20, 2018

Q. The material is 300 series stainless steel that has been abrasive blasted and passivated.

Kyle Major [returning]
- Boss, Missouri, United States

How to QUANTIFY the extent of failure in salt spray test

August 11, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. My situation:
Anyone can help? How to quantify the failure in salt spray testing?

For suppose I found the failure at the last minute or if I see the failure at very little amount?
How to measure the extent of failure in the test.
Because I found the black coloured rust formation on the steel sheet within 140 hours.

Sri Raj
Tester - Puducherry, INDIA

August 2018

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 [affil. link to spec at Techstreet] 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 as the tester to invent pass/fail rules; it is your job to find out where that "140 hours" requirement came from, read the spec that dictates 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!


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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September 10, 2018

Q. Hi,

We have some bolts which are coated with Yellow dichromate. Does white rust appears in this case also?

Sandeep Pawar
- Syracuse, New York, USA

September 2018

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.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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September 13, 2018

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.

Ronald Zeeman
Coil Coating - Brampton, Ontario, Canada

November 15, 2018

Q. Dear all,
Our company uses coating Fe/Zn12/A/T2 on steel and zamak hardware. We start a discussion regarding evaluation of white rust. My question: how should we treat changing of part of coating surface to matte and grey/black color. I don't mean black spots, but whole areas. One of our laboratories claims it is white corrosion but I have doubts.

Anna Borowska Kos
- Gdańsk, Poland

February 6, 2019

Q. Dear sir,

Please share SST hours for Yellow Passivation of 8-10 micron thickness.
Also share details about what is top coat and why it is used

Shilsagar kedare
- Pune,Maharashtra,India

February 2019

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

Pending your 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.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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March 21, 2019

Q. Hi, All, I am Vinodh from a fabrication Industry, I would like to have the experts suggestion on the Structural Painting. We have to supply fabricated structures to the Coastal area. As our customer does not specify any requirements on the test hours, as a general practice how many hours we have to do the test and what is the acceptance criteria. Kindly suggest which standard to refer.
With Regards

- Hyderabad , India

March 2019

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.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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March 22, 2019

Q. Hi Sir, Thank you for the response. We would like to carry out the surface preparation as per BS 7079 SA 3. After surface preparation 2 coats of Primer, 1 Coat of MIO, 2 Coats of Finish Paint. DFT requirement is 325 Microns. For the above painting which type of test is suitable. Environment is coastal areas.


VINODH NAIR [returning]
- Hyderabad , India

April 26, 2019

Q. Hi Sir,
My name is Isvaran. I'm a quality engineer in a zinc die-cast company. We are also specialized in plating including nickel-brass & nickel-chrome. For the first time we coated our zinc die-cast part with high corrosion resistance trivalent chromate. Process: deburring, tumbling, soak clean, acidic etching, chromating, drying at 35 °C for 5 minutes.

We sent 2 different samples (coating & without coating) for SST under the following condition:

1) According to ASTM B117 [affil. link to spec at Techstreet] -2018 modified
2) Testing chamber temperature: 35 °C ±2 °C
3) Saturation chamber temperature: 47 °C ±2 °C
4) Ratio 95% water (De-ionized water or Pure water) / 5% NaCl
5) pH = 6.5 to 7.2 (Measuring at 35 °C)
6) Air Pressure: 1 A ± 0.3 kg/cm square
7) Duration: 48 hrs
8) Test mode : Power off.

The result tested by us is failure due to white rust formation & discoloration on both samples.

But when the samples with the same condition tested by customer, the result was pass. No white rust formed & no discoloration. They just noticed some little black patches after 48 hours. Can you explain what could make the result different?

Isvaran Ramakrishna
- Masai, Johore, Malaysia

May 2019

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.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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September 27, 2019

Q. Hello you beautiful people,

I am a manufacturer of turned components on traubs (automated lathes) and a recent product has me confused with the specifications for plating.
White rust appears 96 hours on a product which is 9 mm in diameter and 5 mm in length with a knurl all around the putter dia.
They have given that the part should must comply with JIS C 0023 for a period or 96 hours.
They do not define the failing criteria of the product clearly (is the 96 hours specifically for white or red rust) and JIS C 0023 simply tells how to do the test without any failing criteria.
Looking further down the thread I found that ASTM B633 [affil. link to spec at Techstreet] States that appearance of white rust at edges does not constitute as failure, but a knurl is nothing but edges.

Am I correct in stating the above to the customer or is there a logical flaw in my thinking?

Navi Kalsi
- - Gurgaon, haryana, India

September 28, 2019

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 [affil. link to spec at Techstreet] should point you in the right direction.

Ronald Zeeman
Coil Coating - Brampton Ontario Canada

September 29, 2019

thumbs up sign  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.

Navi Kalsi [returning]
- Gurgaon , haryana India

Nut with black zinc coating fails 96-hour salt spray test

January 17, 2020

Q. Good Evening everyone,
I have a problem but I'm not finding the root cause of this problem ... a Nut with Zinc Black coating and it fails in SST test within 96 hours (Red Rust Problem)?


January 2020

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?


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

July 15, 2020

Q. Please let us know how to handle samples for salt spray test? Is it mentioned in any standard? If yes then please provide.

Mahesh Kenjale
- Mumbai India

July 2020

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,

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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

August 7, 2020

Q. I have a casting sample hub; I painted it.
My plate sample size (100 x 150 x 0.8 mm) has received 500 hours of salt spray test.

But the salt spray test on the actual casting sample is failing, even keeping the paint thickness at 200 microns.

Found red rust after 48 hrs.

Sandip Vitkar
- Pune, Maharashtra

August 2020

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,

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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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