Dear Sudhakar,
In addition to the restriction mentioned in the trailing mail, control on heat input is more critical in Super DSS materials such as UNS S32750. Based on my previous experience on these materials, I would suggest heat input limit should be 1- 1.5 Kj/mm for smaller thickness and 2 Kj/mm max for thicker sections.
As Mr. Goswami suggested, the ferrite to austenite ratio also critical for G 48 testing. Heat input increases, the rate of cooling would be reduced, and in tern more % of ferrite formation in the final weld. It means that we are allowing more time to transform austenite to ferrite when we use increased heat input. In general the % of ferrite in the weld should be 35 – 65%.
Using lower heat input would minimize the formation of ferrite which is more important for SDSS welds.
Regards,
L. Prabhu kumar,
From:
Sent: Wednesday, June 30, 2010 6:42 AM
To:
Subject: [MW:5792] FW: 5772- ASTM G 48 testing for SDSS
Dear Sudhakar,
ASTM G48A(72 hrs), or and modified versions(24 hrs) is the most common specified corrosion test for duplex or super duplex S.S. This test is considered to be a check of the metallurgical condition of the steel rather than its performance in any service environment. The ferric chloride solution is very aggressive and resembles actual industrial service environments.
For base metals specified test temperatures vary considerably and are 22.5–30°C for 22Cr duplex and 35–60°C for 25Cr duplex(A790, S32750). In ASTM G48A, 72hour test period is stipulated, however shorter version 24hour exposure is also used in the industry.
For 22Cr duplex, the experience from service as well as from testing according to various specifications is extensive and shows that a test temperature of 22.5–25°C is suitable to ensure that materials properties after welding and heat treatment operations are within the limits expected for 22Cr duplex.
For 25Cr duplex, a combination of laboratory test results and service experience, although not as extensive as for 22Cr duplex, strongly indicate that 50°C is a suitable test temperature for solution annealed base metal products.
For welded coupons of 32750 typical recommendations of testing temperature of 400C , and either 24 or 72 hrs of exposure time, with no pitting be present 20X magnification.
From my past experiences in such materials I could advise you on these aspects:-
· Choose the base metal and weld filler metal with ASTM G48A or G48 C (determination of CPT) test done typically @ 50°C
· Monitor welding parameters closely, and stick to the welding heat input of 2-3 KJ/mm criteria. Super Duplex 32750 have a tendency to form excess ferrite, which may to turn to sigma phase, for thick section welding. Composition of shielding and backing gas(Argon+ Nitrogen) would be critical.
· I presume that ASTM G-48A test is not the only test you’re going to perform. If not look out for the test results of Ferrite count test, a good ferrite to austenite ratio and relative absence of sigma phase could be a good way to start for corrosion test.
· Surface preparation of samples could affect the test results. Generally after cutting the samples, the serrations and undercuts should be ground and the specimen should be ground to a 120-grit finish. Under all circumstances use new blades and avoid mix up with blades cutting C.S or LAS.
The test for welded coupons is required to be done in as welded conditions, thus the above guidelines would be of help. I have a attached an article on G-48 test and it’s implications.
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
-----Original Message-----
From:
[mailto:
Sent: Monday, June 28, 2010 8:43 PM
To:
Subject: [MW:5772] ASTM G 48 testing for SDSS
Dear members,
What are the extra special precautions that need to be taken for conducting ASTM G48 Method A test @ 40 deg C for A 790 UNS 32750 material.
Rgds
Sudhakar
Sent from my iPhone
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