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topic 20345

How to compare ASTM B117 Salt Spray and ASTM B368 CASS Test?

A discussion started in 2002 but continuing through 2019


Q. We are plating ABS with 20 microns of copper, 10 microns semi-bright nickel, 10 microns of bright nickel, 2 microns of micro porous nickel and finally 0,15 microns of conventional chromium coating. The Dubpernell Test shows more than 10000 pores/cm2 .

After 30 hours of CASS TEST, hemispherical pits develop in the nickel deposit beneath the chromium topcoat, but the copper is not seen. Should we consider that a failure? Should we consider the parts having failed the CASS TEST when pits appear in chromium layer or when the pits have crossed the nickel layer and copper appears?

We thank you for help.

Norberto Martin
NICRODUR S.A. - BsAs, Argentina


Accelerated corrosion testing is a QA measure often undertaken to get an early indication if something goes out of whack in the processing, such that the components are unlikely to survive the previously expected period in the real world.

Such tests are also often erroneously used as predictors of real life, despite the fact that the corrosion mechanisms are fundamentally different, and the approach will lead to erroneous expectations.

In either application, certain variations in the test procedures for different substrates and coatings may improve their predictive value. ASTM B117 [link by ed. to spec at TechStreet] Salt Spray (Fog) Test (sometimes called "Neutral Salt Spray Testing") is the most commonly applied protocol across the board. ASTM B368 [link by ed. to spec at TechStreet] Copper-Accelerated Acetic Acid-Salt Spray (Fog) Test (CASS test) is another widely used accelerated corrosion test, especially for nickel-chrome plated components.


A. Some automotive fuel components have this type of plating and CASS testing. We use both an appearance criteria (5% red rust at 24 hours) and a functional requirement (a burst test at 72 hours).

The interpretation of CASS and any other corrosion test data is always subjective and open for debate. This sort of thing is usually agreed upon between a customer and supplier based on technical experience and judgement. I have not seen an industrial requirement that uses a microscopic analysis of pores or corrosion sites. It could be done, but would you want a manufacturing process that requires constant microscopic analysis of test parts? This type of analysis may be better suited to research or an initial validation.

I suggest you strike up this conversation with a nickel-chrome plating chemical supplier.

tim neveau
Tim Neveau
Rochester Hills, Michigan

To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.


Q. 1. How to compare ASTM ASTM B117 [link by ed. to spec at TechStreet] Salt Spray and ASTM B368 [link by ed. to spec at TechStreet] CASS? If component resists 200 hours B117 test, how many hours should it resist for B368 test?
2. What is organic coating? Inorganic coating? Chrome plating is organic or inorganic?


Xiao Liu
- Nashua, New Hampshire


A. 1. The only way to accurately and reliably develop a correlation is to build one yourself. That is, put some parts in neutral salt spray and some in CASS and see what you get. Keep in mind that both tests have significant variability, so it'd actually take numerous tests, control panels or parts in both tests, multiple cabinets, etc.


NSS = Neutral Salt Spray, i.e., ASTM B117

SWATT = Sea Water Acidified Accelerated Test, described in Annex 3 of ASTM G85 [link by ed. to spec at TechStreet] Standard Practice for Modified Salt Spray (Fog) Testing

People often ask these types of questions, especially for SWAAT and NSS. There is no simple formula or factor to convert one test to another. They all induce different corrosion mechanisms on different substrates.

BTW, my investigation found that CASS was developed for Ni-Cr plated parts in Detroit. I talked to a guy who worked on the test, and he told me that they eventually determined that 8-12 hours in CASS meant 1 year in Detroit's environment (in the 50s or 60s). If you're not doing Ni-Cr plated parts, technically you're not even using the right test. Then again, I've seen lots of people use CASS (or NSS or SWAAT for that matter) with no idea as to how the test was developed or what its original purpose was. I'm sure many can relate.

Christian M. Restifo
- Pittsburgh, Pennsylvania

Corrosion Tests and Standards, Application & Interpretation
0-15V 0-5A


A. Hi Liu

2. Organic coatings are coatings that are based on organic chemicals (basically chemicals that contain carbon). Most paints and powder coatings would be organic coatings. Inorganic coatings are coatings that don't contain (significant amounts of) organic chemicals. Metallic coatings like galvanizing and nickel and chrome plating are inorganic. There are probably some blurry areas, as there almost always are. Good luck.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

2006 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We manufacture parts for mostly military end use. Our parts generally are aluminum with Cad Plating over electroless nickel plating. Has anyone ever compared CASS Testing with the standard neutral salt fog spray testing? We are developing an alternative to Cadmium plating, and if there is a comparison that someone has done, it would be great to find the results of the comparison, i.e., one hour (or 7 hours) of CASS = XXX hours of ASTM B117.

Tom Saxe
Manufacture aerospace products - Chatsworth, California, USA



One of the reasons predictive correlation of accelerated corrosion testing to real life is problematic is that the corrosion mechanisms are fundamentally different.

For example, hot dip galvanizing is no doubt the most durable of any finish, often surviving on electrical transmission towers for 75 years or more with no maintenance. This is because it is a relatively thick zinc coating which (under favorable conditions) reacts with the small amount of carbon dioxide in the air over the months and years to form tight, non-porous, almost glass-like, complex zinc carbonate reaction products which greatly slow the corrosion of the zinc. In a salt spray chamber these carbonate reaction products can never form, and zinc corrodes away quite quickly.

A. Hi Tom. If someone can suggest which of the two tests is better for your situation, or can propose another test, that would be great. But we appended your inquiry to an earlier thread which touches on the difficulties of correlation. Unfortunately, I think the answer is that you will not know the real world life of your cadmium substitute, nor how it compares to cadmium in the real world, except by real world testing. And only after that can you build a correlation to accelerated testing. While developing correlation can be useful, trying to develop a predictive correlation that doesn't require real world testing probably won't work. Many have tried.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.


Q. Sir,

We, the pioneer in auto electrical manufacturer in India, do various types of high corrosion resistant plating/coating systems based on customer requirements (in case 720 hours NSS is the requirement, we need to wait 30 days for the result).

Is there any other accelerated tests available to correlate NSS test to avoid the longer time? Can we correlate NSS & CASS tests? For What application & evaluation CASS test can be recommended?

Thanks in advance.

P. Narasimhun
- Chennai, Tamilnadu, India


A. First a side note about CASS. A few years ago, I tracked down a gentlemen who was involved in the original development of CASS. According to him, CASS was used for chrome plated bumpers. 8-12 hours in CASS correlated to 1 year performance in Detroit in the 50s/60s. (He didn't say how they defined failure in the test or the field.)

Those in the business know that CASS is used for a bunch of things, yet you'd be hard pressed to find anyone who could tell you *why* the test is used in a specific instance. (You could probably say that about a lot of these tests.)

That said, you generally cannot correlate accelerated tests to tests such as NSS for numerous reasons. The corrosion mechanism may not (and usually is not) the same, and CASS (and even NSS) is not representative of what goes on in the field. Salt cabinets (assuming they're run properly, which is generally not true) also have a great deal of variation that makes any correlation, in my opinion, greatly suspect.

That said, I have seen some published R&D that correlates electrochemical tests (DC/EIS) to NSS for painted parts. Note, however, that you must develop the test yourself. You cannot simply pull a "method" off the shelf and say that an expected corrosion rate of x mm/yr in an electrochemical test corresponds to y hours in NSS. You must take the time to develop this correlation yourself because it depends on the paint, substrate, chamber, and test equipment.

Christian M. Restifo
Circle-Prosco, Inc. - Pittsburgh, Pennsylvania, US

2007 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I'd like to speed up our 1000 hours for coil coatings requirement of ASTM B117 [link by ed. to spec at TechStreet] . I'm planning to use CASS test. Is it comparable? If so, what will 1000 hours of B117 equivalent to CASS test.

Raphael Atienza
Twin aces industries - Philippines


A. CASS is not comparable to NSS, at least not in any generic way. It will give you a different corrosion mechanism.

If you want to use CASS as a proxy for NSS, you will have to very carefully develop your own correlation which will depend on the substrate, paint, even the cabinet(s) themselves. You'll also have to run periodic tests to verify that your correlation is still correct. This assumes, of course, that you're running the test purely as a quality assurance test to make sure your process is running the same sample to sample. If you're trying to mimic some field failure, you're talking completely different corrosion mechanisms....

Christian M. Restifo
Circle-Prosco, Inc. - Pittsburgh, Pennsylvania, US

July 25, 2012

Q. May I ask a question about Salt spray test and CASS? We have a standard salt spray test equipment, but we want to do CASS test on this equipment. Is this possible? If it is, what should we do?
Thanks for helping.

Kerem Kurkcu
- Izmir, Turkey

A. Hi Kerem. The supplier of your salt spray cabinet can advise you on this, but if not, it would be best to get access to ASTM B368 [link by ed. to spec at TechStreet] because it specifies the equipment and procedure required. It's only 4-5 pages, and then you won't be guessing whether your procedure complies :-)


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

In CASS test we get rusting only on knurling

February 24, 2014

Q. We have checked the part for 48 hours CASS TEST but we have observed the rust only on the knurling area.

So my question is whether there is any specific requirement of CASS test for threaded, knurled area?

Pankaj Mahajan
- Gurgaon, Haryana, India

February 26, 2014

Hello Pankaj, which exact standards does your CASS test comply with?

Davey Shaw
Shenzhen, Guangdong, China

February 27, 2014


Pankaj Mahajan [returning]
- Gurgaon, Haryana, India

February 27, 2014

I doubt the standard gets that specific, it is probably more a matter to discuss with your customer. If they only require that the non-knurled areas pass CASS, then you should be fine.

Are these parts stainless steel, or a non-ferrous alloy perhaps? If the knurling process is causing iron contamination, passivating the parts should help.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

July 25, 2014

Q. From many threads I can see that there is no relation between NSS and CASS. But I see in some webpages, which claims that CASS is 9 to 15 times faster to NSS? Can we take this as a thumb rule?


"Atmospheric factors affecting the corrosion of engineering metals"
by Seymour K Coburn
from Abe Books
info on Amazon

July 2014

A. Hi Praveen. You appear to be acknowledging that there is no correlation, but then asking whether the correlation would be 9-15:1 if there was a correlation? :-)

I think it's true that CASS is more aggressive than NSS and will always be faster. Other than that, any correlation there may be would only be for a given plating on a given substrate ... because how much more aggressive the CASS solution is would depend on what you are trying to corrode with it.

The origin of your 9-15:1 ratio may be that copper-nickel-chrome coatings are sometimes spec'd to pass a few hours in CASS, but several times more hours in acidic salt spray or neutral salt spray. Good luck, but please accept the general thrust of this whole thread that any correlations between CASS, NSS, and real life are at best no better than the backup data for your parts that you have accumulated to demonstrate them :-)

Luck and Regards,

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

September 18, 2014

Q. I am curious, does anyone know how many hours of CASS testing would be comparable/estimated to years a vehicle corrosion "in the field" would be. I understand that would be a estimate (especially considering there would be a difference between what part of the country the vehicle would be "in the field").....I am just looking to see if anyone has an opinion on this question.. I am specifically questioning/asking 48 hours or 80 hours of CASS replicate the amount of corrosion would equate to years of a vehicle would see in lets say Michigan...
Any opinions or thoughts would be appreciated..

Derrick Wolfe
- Grand Rapids, Michigan USA

September 2014

A. Hi Derrick. Back in 2002 Christian Restifo expressed his belief that "CASS was developed for Ni-Cr plated parts in Detroit . . . they eventually determined that 8-12 hours in CASS meant 1 year in Detroit's environment (in the 50s or 60s)."

But Christian also remarks that there is significant variability throughout, such that you need multiple tests, multiple panels in each test, cabinets from different manufacturers, etc.

And I need to repeat, so that your Q&A can stand on its own without being misquoted, that this correlation applies at best only to nickel-chrome decorative plated parts. Other materials and coatings corrode in fundamentally different ways such that CASS test results have essentially no bearing on their anticipated life. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

sidebar2 September 19, 2014

thumbs up signThanks for your response Ted, appreciate your time!

Derrick Wolfe [returning]
- Grand Rapids, Michigan

September 2014

Hi again. Way back when (way, way, back when) I was chief engineer of the Equipment Division of Harshaw/Atotech and we built a very large plating-on-plastic line for the company you work for. At the time, it was perhaps the biggest plating-on-plastics line in the country. It was a blast from the past hearing from you :-)


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

December 17, 2019

Q. Hi
I want to do salt spray test on the stainless steel by CASS method but I haven't any information about it. As well I know we don't use the method for stainless steel. But the NSS method test duration is too long, and I have little time.
Thank you all.

ahmad reza jannat
- isfahan iran

December 2019

A. Hi Ahmad. You can learn the details of CASS testing in ASTM B368 [link by ed. to spec at TechStreet] or ISO 9227 [link by ed. to spec at TechStreet]. Still, such tests are designed for QA: that is, if the parts previously survives X number of CASS hours, and they no longer do, something has changed that will probably reduce the life of the component in the real world. But establishing an initial correlation between this QA test and real world life can be a challenge; and to assume that X hours of CASS equals Y months of real world exposure is highly questionable, and depends on the type of component, the exposure conditions, the substrate, etc. For example, does accelerating the corrosion with copper really have any relationship to the actual exposure? Good luck.


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

December 18, 2019

thumbs up sign  Thanks a lot dear Ted

Q. I read those standards but I can't find any information about stainless steel salt spray with CASS method.
Do you know for example X number of CASS hours is equal how long number of NSS method?????
Did you do any experiment on the stainless steel salt spray?

ahmad reza jannat
- isfahan iran

December 2019

A. Hi again. CASS is more severe than NSS, but as has been said many times on this page, I don't think any further correlation is possible.

Do you passivate your components, or do you electropolish them. What alloy(s) are they? Thanks.


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