Strange SDD steel weld corrosion test result

[Liuk]

Dear all!

We have received very strange SDD pipe welded joint corrosion test (acc NORSOK M-601/ASTM G48) result. Weight loss is 40 g/m2, but no pitting on sample surface. Pickling (5%HF+20%HNO3) was performed before corrosion test.

Micro examination result is acceptable: no continuous precipitation and intermetallic phases.

Ferrite content is adequate too: cup 56%, root 46%, HAZ -59%, BM-50%.

Weld quality is good: no external/internal defects.

We perform about 10-15 corrosion test in week and we haven't gotten result like this.

Is it possible?

Thank you in advance!

 

[metengr]

Double check your mass loss, sounds like an error.

 

[Liuk]

Thank you very mach!

We have performed triple test: result the same: 38, 44 g/m2. New test solution was used in each test of course. Samples were prepared acc. ASTM G48 as usually...

It seems as error, and I can't understand it. We never have result like this. If weight loss was big there were some pits on sample surface and we have problems with micro structure (sigma phase).

I really don't know what shall we check yet.

One doubt: heat tint in root was up to bluish...

 

[EdStainless]

But if you pickled it then you removed all heat tint, right?
Why would you pickle it, don't you care about the actual surface being used?

What was the test temperature?

There are a few things that could cause this.
Have you done a chemical analysis, on both base and weld filler?
Make sure to check N also.

I would also look harder at the micros, alpha can be very difficult to see.


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Plymouth Tube

 

[Liuk]

Yes, heat tint was removed. But as I understand surface metal Cr content is smaller under heat tint.

The corrosion test is part of welding procedure qualification acc. to NORSOK M-601. Sample shall be pickled before corrosion test acc. to this standard.

Test temperature acc. to NORSOK is 40 C. This temperature is lower than CPT for UNS S32760 as well as for filler material (OK 2509).

We will check chemical composition after Easter holiday, but unfortunately we can't determine nitrogen content using our optical emission spectrometer. But tensile properties (welded joint break location is BM) and BM ferrite content is very close to values indicated in material certificate.

Our microscope max. magnification is 1000x and it isn't enough for alpha revealing...

Very many secondary austenite in root, but..

No pittings at all! Is it possible for weight loss 40 g/m2 (0,15 g)?!