Micrographic Examination for DSS 1

[energpart]

Hello,

Our company supply valves for the OnG industry. One job in particular has us supplying Duplex SS ball valves.

We submitted Mill Cert for end user review. They rejected and commented to have each heat be micrographically examined at 400x minimum to check for absence of grain boundary carbides, sigma, chi and laves phase. I checked and they did have this requirement in their project specification.

Problem is, the valves has already been delivered and there is no more test sample at material lab to do this micrography. The comment(s) came much later.

I tried to counter by asking them to refer to the micrograph from ferrite count which was done according to ASTM E562 19e1 to look for these phases. Also, that mechanical and corrosion test found acceptable to supplement no defect to microstructure. But, still not acceptable.

I attach one of the micrograph for ferrite count here for you guys to help clarify if you can't indeed check for the phases as per comment. I am not a material science expert and neither is the end user's engineer.

As my initial respond is rejected, do you guys have any suggestion on how to best respond to this comment so that they will accept the material(s) ?

Our manufacturer is on another continent and can't support much. They have no expertise on material science and there is no more heat lot to sample.

Thanks.

 

[dik]

I cannot answer your question, but it piqued my interest, and I found this site:

https://vacaero.com/information-res...of-phases-in-stainless-steels-by-etching.html

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EdStainless]

It is not uncommon for duplex customer to require both micros and another A923 test (corrosion or low temp impacts).
On problem with the attached micro is that it is etched for maximum contrast, not for finding secondary phases.
I would think that if you did A923 C and passed you have some grounds to appeal, but in the end you may need to take a few valves back and cut them up for samples. If it was in the order then you are responsible for it.

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P.E. Metallurgy, consulting work welcomed

 

[energpart]

Thanks for the input.

We did actually do pitting corrosion test in according to ASTM G48 and impact test at low temperature with no issue. I'll try to respond to the comment with these reports.

Regarding the attached micro, if sample(s) from corrosion/ferrite test still available, is it usually possible to grind/sand down and re-prepare the existing "over"-etched surface to check for the unwanted phases ? Or is the sample only good for one time use and examination.

 

[EdStainless]

G48 is not a test for intermetallics, you can pass G48 and fail A923 and vica-versa.
Yes, you should be able to repolish the sample and then etch for phase evaluation.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

I attach one of the micrograph for ferrite count here for you guys to help clarify if you can't indeed check for the phases as per comment. I am not a material science expert and neither is the end user's engineer.

Do not attempt a determination based on a printed micrograph, or worse, one that has been scanned. Grain boundary precipitates are very fine and the assessment should only be made live through the metallograph by a metallurgist or experienced lab technician (experienced with DSS that is).

You did not receive what was committed to you by the material supplier and/or testing organization, and now you are in a position where you do not meet your client's specification. You need to find some representative material somewhere; is there some dead stock you can take from somewhere on the valve body that will not impair it by removal?





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

 

[M.CH]

Hi,

If you obligated to perform metallographical examination, in-situ metallography may be possible check with laboratory expert.

 

[energpart]

I will try to ask for a waiver stating no sample availabe and see how it goes from there. The valves has already been installed and currently being used.

This is an initial purchase for tube rupture study purpose so there is a good chance will be accepted. Purchase for actual application will depend on this study.

If you guys can suggest a better wording/justification it will be much appreciated.

 

This is an initial purchase for tube rupture study purpose so there is a good chance will be accepted. Purchase for actual application will depend on this study.

What kind of study will validate the long-term corrosion resistance of the DSS material?
You are asking for a waiver on the most significant reason you are paying for DSS...?

If you obligated to perform metallographical examination, in-situ metallography

I have done it myself on a P91 valve body on a lab bench. A lot more comfortable than climbing up vertical ladders with my kit to work inside a dirty tank at 90°F in a refinery...

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