[MW:7843] MW: 7800- Intergranular corrosion failure in 304H

Hi Srini,

Looking at the issue, 304H plates could bring surprises, through sensitization while welding. Due to higher "C", some grain boundary carbides would precipitate in this alloy. Unless precipitation is major, it would not cause failures during exposure to boiling ASTM Practice E solutions.

As this is procedure qualification you have no choice but to repeat the test. However investigation of some of these facts might help:-

Perform ASTM 262 Practice -A (oxalic acid test) test on the base metal. Presence of any ditched or end grain structure would make it a suspect. If so repeat the IGC -E for the plates.
Work out the correct heat input for, typically 2--2.5 KJ/mm. The values mentioned below 60KJ/in ( I presume) works out to be 2.4Kj/mm max, which is not very high. However keeping Q strictly in that range would help. If required reduce the Interpass Temperature to 125 deg C max. However looking at the data posted below, I do not major flaws with welding parameters.
Confirm that IGC Practice E test results are also satisfactory for welding fillers.
How was bending performed, by hammer or hydraulic press. The later method would be better.

I would think the scrutinizing the above would help to get PQR through.

Thanks

Pradip Goswami,P.Eng.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net

-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Srini
Sent: Monday, October 25, 2010 5:16 PM
To: Materials & Welding
Subject: [MW:7800] Intergranular corrosion failure in 304H

During a procedure development for nuclear component, the HAZ /Weld metal interface region is failing in ASTM 262 Method E test. Carbon content of 304H plate is .07%, GTAW (manual process), Heat input 60KJ max, Interpass temp 150°Cmax. Filler 304L, size 3/32", plate thickness 1/2".
Fissures are found during bend test after 15hours soak in 16%Sulphuric acid. This occurs at HAZ interface.
I did a micro at failure portion and found Chromium carbide precipitates along the grain boundary and cracks along the grain boundary.

Plate material was ordered to pass 262 Method E and it was reported as passed. 304H is non stabilized grade and it has to be H for the application. Solution annealing cannot be done due to size of the component. What are your suggestions / tips to fine tune welding and get rid of this problem?

Thanks in advance.

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