ASTM G48 Tests

[Angsi]

The duplex stainless vessels are to be operated at temperature well above 60 deg C on an offshore platform.

As part of inspection and testing requirements during fabrication process, is testing to ASTM G48 necessary (due sensitization and emrittlement during welding process)?

What should the test temperature be held at? And what is the industry's acceptance criterion?

Thanks.

 

[Goahead]

You may find some information in the following page

http://www2.sandvik.com/sandvik/014.../HandbookWeb/4D2F725116DAD2ABC1256B490043561E

http://www.welding-advisers.com/

 

[metengr]

The G48 test results will confirm a CPT in comparison to published values for this material. However, this is really not an acceptance test, I have seen others refer to a "modified G48 test". However, you need to spell out specific test variables and practice.

Frankly, corrosion testing using ASTM A 923 Test Method B to verify a proper solution anneal of the duplex material used in vessel fabrication is most cost effective, and more important. If you specify Method B, this can be used as part of the qualification of the weld procedures and would provide more meaningful results.

 

[Angsi]

Thanks. For the following case:

- Offshore environment (tropical)
- DSS vessel design temperature at 100 deg C
- Vessel content hydrocarbon fluid

Will it be valid if I specify the test temperature to be 100+15=115 deg C and the concentration (corrosivity) of the FeCl3 solution to be similar to the seawater? Isn't the objective to ensure that the DSS has been supplied properly solution annealed and it is able to withstand the corrosive external environment?

 

[metengr]

Yes, the test temperature is acceptable and actually it would be considered artificial sea water. However, what is the point of only specifying the ASTM G48 test? As I stated, your concern should be an acceptance test that the duplex ss material received has been properly mill annealed, and you have demonstrated that after welding (with NO PWHT), the impact test properties are adequate. This is important because you do not want to embrittle this material during fabrication of a pressure vessel. ASTM A 923 Test methods can be easily done with weld coupons.

 

[Angsi]

metengr, you are going a bit too fast for me. So the ASTM G48 is for testing the base material where as the A923-B (impact testing) and ASTM A923-C (pitting corrosion test)for can subjected on weld? In other words, am I correct in saying the following combination of tests may be possible for the pitting corrosion:

A) ASTM G48 for the base metal and A923-B and C for the weld coupons
B) Better still A923-C for the base materials and weld coupons + A923-B for the weld coupons (at the lowest design temp)?

 

[metengr]

Yes. I would go with B. Get your hands on a copy of ASTM A 923. It is well worth the reading.

 

[SJones]

Ferric chloride will bear no resemblance to the fluid in the vessel and, therefore, it is no use relating the test temperature to the operating temperature. It is a coarse quality control tool that has evolved over the years. Take a look at NORSOK standards such as M-630 or M-601 to get an idea of the consensus "standard" test conditions and acceptance criteria adopted by the oil and gas industry.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/