Hello Safa,
What's the piping design code? I did not see any clause in B-31.3,which calls for "allowable stress values should be chosen in accordance with the hydro test temperature which should be lower because of excessive PWHT". I may be wrong also ?
If you're fabricating P-91 spool then 7300C is not a high or very excessive temperature. This temperature or more is the recommended PWHT temperature range for this steel.
7300C or more typically is the annealing temperature range for carbon steel. A test cap welded and heat treated repeatedly in the annealing range will get softened considerably and eventually may not withstand the hydro test pressure. So as a rule of thumb they should not be reused more than once, unless there're documented proof of material properties.
Prior to reuse grind well so as to ensure previous weld metals and HAZs are completely removed.
Alternatively I would say the suggestions of Mr. Karthik is quite practical, since it may ensure safety during hydro test.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Karthik
Sent: Monday, August 30, 2010 5:07 AM
To: materials-welding@googlegroups.com
Subject: RE: [MW:6776] PWHT of dissimilar materials
| Hi, You can do PWHT before hydrotest without caps by add (200 to 300mm) small length of same P91 pipe to the existing pipe spool .After PWHT, you can weld the hydrotest cap to the end of added pipe length. After Hydro test finished you cut the excess length of the pipe with cap. This will be the best one, if you concern about the caps durability. Thanks & Regards, (karthik) Karthikeyan.S QA/QC Manager Getabec Energy Co.,Ltd. 379,Moo6,Soi8,Nikhomphatana, Rayong-21180, Thailand. Phone: 0066 38 897035-8 (Off) Fax: 0066 38 897034 Hand Phone: 0066 892512282
Dear John, Thanks for your reply, but as per our design codes PWHT should be done before Hydrostatic test. Safa From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Johnson Madukayil Why do you have to keep the hydrotest caps on after hydrotest? I would advise you to remove the caps and then do the PWHT. On Sun, Aug 29, 2010 at 11:23 AM, Safa Özhan <safaozhan@gmail.com> wrote: Dear All, After welding of caps are completed, we heat treat the spools together with (most of the time caps made of dissimilar material, mostly CS Caps because -- -- |
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