Corrosion test for UNS 31254 in fittings vs forged flanges.

[Ratheesh_n]

Members,

One of client specification mentioned corrosion test G48 method A with duration of 24 hours for forged flanges for UNS 31254 material. But for same UNS 31254 fittings(formed from pipe or plate) G48 method A with duration of 48 hours. Please tell why there is a difference in the duration. Acceptance criteria and method is same for both.

1. Why there is difference in the duration for different product form
2. Is forge material is more corrosion resistant compared to the hot or cold formed fittings or pipes.

 

[EdStainless]

For these more corrosion resistant alloys we always used 48hrs.
What temperature did they request?
I presume that they want the surfaces left as-produced.
It is typical to allow mechanical polishing of cut surfaces though.
You need to find a very experienced lab to do this testing.
The mixture needs to be correct and temp needs to be +/-0.5C.
And even then repeatability of the test is poor.


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P.E. Metallurgy, consulting work welcomed

 

[SJones]

The difference is probably down to the quality of the engineering contractor, and the quality of the checking by the client.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

And method A is not preferred.
Method C will be more reliable.
Sounds like people don't really know what they are asking for.

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P.E. Metallurgy, consulting work welcomed

 

[SJones]

@Ed agreed re method C, however, the difficulty comes in setting the temperature of the acceptance criterion. Method A is selected because it has a set temperature, and doesn’t require multiple tests to ramp the temperature up. It’s even found its way into accepted standards for testing 625 at 50 deg C - a complete waste of time because even defective 625 will pass at that temperature. Just a few months ago, I was attempting to force several manufacturers into testing 625 clad products via method C with a single test temperature of 75 deg C. I got nowhere because the manufacturers had never had to do it, and they weren’t prepared for what they saw as a risk. We ended back with method A at 50 deg C to cut short the arguing.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

For high performance alloys (super austenitic, super ferritic, super duplex) we tested every lot with Method C at a temperature that was 15C below the published CPT (temperature of first pitting).
If they have been HT wrong, it will show.
If they are correct, then they pass easily.

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

 

[Ratheesh_n]

@EdStainless test temperature is 50 deg for both the cases. surfaces of the specimens is in the “as delivered” condition for testing.

 

[Ratheesh_n]

@SJones Requirement is same for all contractors and vendors. So, it's not related to the quality of contractor/vendor. Thats what the reason we wanted to know the metallurgical background.

 

[SJones]

@Ratheesh - I was referring to the quality of the engineering contractor who drafted the specification. The client then never checked the defective specification properly before issuing it for use.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.