Verify 316L

[Ivan krakow]

We recently purchased a number of 14mm 316l plates with MTR's.. However as a further step to ensure the quality of the 316L , we had samples tested on a Spectro Max spectrometer.. What we fond was that our samples did in fact indicate that this was 316L, but the composition % were different then what the original MTR's indicated. Is that normal? as I guess all testing machines will e slightly different.. This is my assumption, but would like to hear from others.

Thanks in advance
Ivan

 

[EdStainless]

Of course they are different, the machines and calibrations are different.
It would not even be uncommon to find some elements out of the original heat spec range, but within the allowed check tolerances.
There are special check tolerance requirements.

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P.E. Metallurgy, Plymouth Tube

 

I've observed that the growth of PMI (not the same as your instrument, I know) has been driven by growing mistrust of vendors. On a typical chemical plant pipe spool job, the same items will be tested three or more times between arrival at the contractor shop and field installation. This looks like a substitute for a quality system (or compensation for lack of same).

I've also noticed (at least in the nuclear industry) a tendency to overtest materials. This can mean tests that are not relevant to the design/service requirements, or multiple tests that yield similar information. More testing does not improve a product...

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[arunmrao]

At least for Carbon content in 316L, the analysis report should not be far different. One report might read 0.025% C and another might read possibly 0.027%. which to my mind is not very alarming.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

One report might read 0.025% C and another might read possibly 0.027%. which to my mind is not very alarming.

That is less than the variation within an item, and less than the measurement uncertainty.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Dhurjati Sen]

Dear Ivan,

State the Spectrometer result and also mention the material standard of 316L.

Regards.

DHURJATI SEN

 

[weldstan]

When I worked on the Space Shuttle over 40 years ago, we placed the same specimens in 7 different labs for spectrographic analysis and then compared the results with a wet chemistry analysis by the most respected chemist in the Southern California area. All of the spectrographic analyses were different from each other. We selected the lab with the closest analysis to that provided by wet chemistry to perform our analyses on rocket part metallurgy. As EdStainless stated there will always be differences between different spec analysis lab results. Do not be surprised. Be very surprised if they were the same as that on the MTR!

 

[EdStainless]

We get MTRs with both Heat and Check (or product) chemistries on them, they are often rather different.
A carbon variation of 0.021% on one and 0.028 on the other would not be uncommon. And these are from the same heat of material tested in the same machine.
Other elements will have smaller relative variations. Mo will have a heat analysis of 2.06 and a check of 1.98 commonly, which are both fine.

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P.E. Metallurgy, Plymouth Tube

 

[bobjustbob]

Your supplier did not test that specific piece of material. They took a representative sample in one part of the entire heat. They probably took multiple but they have a standard place inside of the heat to be most representative of the whole. Depending on their heat size and casting method the chemistry can change throughout the heat. In a continuous cast situation you have a certain amount of mixing from one heat to the next that can change the chemistry.

Look at the uncertainty in your check standards. The supplier is using similar standards. That is the uncertainty just in the check standard. That does not take into account all of the other minor difference like surface prep, optic cleanliness, gas cleanliness, etc..

In the case of light elements like Carbon and nitrogen your supplier probably used a combustion method instead of an OES. I have used a spectromax with the UV optic and it did give useful carbon and nitrogen, much better than the older 90's era spectro's, however, the LECO was more stable and give more consistent results.

You should probably familiarize yourself with the product analysis section of the ASTM standard that you are ordering to. For example ASTM A480 in Table A1.1 lists the tolerance over the maximum for Carbon Between 0.010 and 0.030% as .005%. So, if you perform a product analysis the acceptable carbon maximum would be 0.035%.

 

[Deanlover]

I think this is acceptable,
different machine and different method also can make the difference.