American Welding Society Forum
I have been running into a lot of stainless suppliers that have cobalt in their 316 Stainless. The ASTM/ASME specs make no allowance for cobalt however on the web I have found some papers that say cobalt is allowed by some of the EN standards. I can not get EN standards though. Some of our European suppliers that supply to EN are the ones with Cobalt but I have even found it in US suppliers who hold to ASTM/ASME. One European research paper I found says the limit is .20 but most of the suppliers are at .3 or so. One US supplier today even had as much as .5 Co in a 316. Should I be concerned about this???? I get annoyed when I can not find these kinds of answers.
I heard rumors about cobalt in stainless a few years ago. I guess I forgot about that scare.
Cobalt is common for jet engine parts. In my last job we welded a lot of Kovar which is similar to stainless or Hastelloy except it has small amounts of Cobalt. I don't think it was properly sorted in the scrap process. They often would throw stainless, Hastelloy, and Kovar all into the same recycle bin. If the the steel mills do not run a PMI test on every little piece then it all goes into the mix.
I went through 500 pages of material cert reports today on an audit and nearly every stainless supplier had cobalt in the chemistry reports. My first thought is that it would increase tensile strength and hardness but it might hurt impact values - but we do not test 300 stainless for impacts so...
I don't know which one it was for sure. Now I am curious. I will look at the Kovar specs. It is used to increase hardness in wear applications.
I read all the links. Thanks they were great information. Kovar has 17% cobalt but I don't know which cobalt it is.
The 316 stainless I saw today had .5% cobalt worst case. It was blessed by the "certifiers". Now it might be in a finished pressure vessel for all I know.
Just got back to forum -
In the old Nuclear days we had a govt spec MIL S 23195 which was originally set at 0.2 % Co in types 304 and 304 ELC.
. . . . that spec was active up to about 1965 and then it was replaced by MIL S 23195 A which had an upper Co limit of 0.10 percent which was active all the time I was in the nuclear industry. In 1991 there was a proposal to make a MIL S 23195 B with a Co limit of 0.05. That 0.05 spec did not get adopted because this was in the noise range of the detection limits.
I had a case with MIL S 23195 A with 0.09 Co which was rejected by Portsmouth Naval Shipyard because their incoming check analysis showed 0.11 % Co. My boss taught me a really good lesson . . . . and had me cut a piece off of the bar in question and then take it to another department and cut it into 4 pieces like a pie. We then sent 1 each of the " pie "pieces to 4 mills which did 100 's of analyses each day and found out something verrrrrry interesting - the mills which calibrated their spectros with lower value standards gave us lower results values and the mill which used the highestvalue standard gave the highest result !
The real purpose of this is what is the point ? In our application we were trying to fabricate low cross section parts and it was thought quite logically " Lower Cobalt means less radioactivity ".
What are you trying to do ?
I know this may shake you up but some of the imported SA / A 516 Grade 70 made in Russia has reported in the analysis the Arsenic content of the steel -
So again what is the purpose of what you are doing ? INCO Nickel listed the ( Ni + Co ) content as one value -
Some of the material was bars and some was plate. This is for oil field equipment. It could be a pipline, drilling rig structure, or pressure vessel. I did not dig deep enough to find out what the end application was. When vendors submit material certs it is for an entire contract. In this case I had to review 500 pages of material certs. Review included check of chemistry, mechanicals, and certifying inspectors stamp stating conformance.
Just a question -
When your inspector accepts a copy of someone's cert for chemistry/physicals what does he check off ?
Let's say it is for 1" thk sa 516 -70 - In the case of 1 % Cerium being reported would the inspector check it off
because it was there or just circle it to acknowledge it was there with no limits ?
The vendor inspector signs the cert for conformance to spec and our inspector checks it audit style and stamps it with a special stamp. Then it goes to engineering where we do our own audit mainy cr, ni, and mo for stainless and mechanicals for tensiles. Just a quick overcheck. I did 500 pages in 4 hours and that is when I found the Co as an outlier in chemistry.
Actually, while there is only know known stable isotope of cobalt (mw=59), the standard molecular weight of cobalt of 58.933195g·mol−1, recognizes that other isotopes are always found with cobalt in nature, albeit in very low proportions.
What's interesting, is that all isotopes of an element have the same chemical properties (because their electron shell is the same, since they have the same atomic number and hence nuclear charge), so cobalt sulfate found in nature will contain cobalt of many isotopes.
This is much like heavy water, which contains heavier isotopes of hydrogen (duterium and tritium are names for hydrogen with a mw of 2 and 3 respectively), and which can be found in all bodies of water, just in very small proportions. Interestingly enough, Isotopes of oxygen are also found in water, and the ratio of the isotopes of oxygen in ground water is being used in surveying, to give an estimate on the "age" of the water (as it relates to how quickly that groundwater is replenished from rain water), to determine the long term viability of pumping from an aquifer.
Oh, and yes, I get the joke. :)
The chemical analysis for stainless plate under ASTM A240 is required to be meet both A240 and A480 (general requirements). A480 contains the following provision:
6.2.2 All commercial metals contain small amounts of
elements other than those which are specified. It is neither
practical nor necessary to specify limits for unspecified elements,
whether intentionally added unspecified elements, residual
elements, or trace elements, that can be present. The
producer is permitted to analyze for unspecified elements and
is permitted to report such analyses. The presence of an
unspecified element and the reporting of an analysis for that
element shall not be a basis for rejection, unless the presence of
that element causes the loss of a property typically expected for
that metal, for the type and quality ordered.
Thanks. That really clears things up for me. The certifing authority engineer on the project I was working on insisted that the ... in ASTM specs meant not allowed. At any rate, my contribution to the project is complete. The project is winding down, my contract has expired, and I am no longer responsible for working this issue. We did request the supplier to explain the cobalt I think but I don't think we rejected the certs. This has been a learning experience for me at least.
The paragraph Marty posted is a very telling, and typical paragraph. Think of who it is that actually sits on the committees that determine these rules.
They are not going to allow too many opportunities for rejection. This is not irresponsibility. Far from it. It is more often well thought out, intelligent, and common sense. Those of us without extensive material experience have a tendency to lose sight of common sense. For example rejecting something due to ......
When responsibility is combined with ignorance common sense will be the first casualty.
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