Debasis As David Henderix has pointed out, go for the latest code API 650 or API 653 and follow the code restrictions/ rules for new design tanks. Answering your question on API 650 if it is still ordered and still under implementation under API 650, API 650 is clear than any shell to shell plate thickness exceeds 1" , it has to be mandartorily PWHT for Group I,II, III, III A materials. No designer or fabricator can deny doing PWHT if plate thickness exceeds 25 mm (>1" thickness) . For 30 mm thickness shell to shell plate (whether verttical ror horizontal welds between shell plate to shell plate or shell plate to nozzle welds), designeer and fabricator has to mandatorily carry out PWHT as per old API 650 amendments till 2000. API 653 code refers to the same and has not changed on this PWHT for thickness > 25 mm. You can insist on PWHT for 30 mm thickness plate to plate welds - both contractually and insist on meeting to code regulations as well. Trust this helps you. C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India July 17 E-mail:nishi@vsnl.com >Debasis: > >Please note that API 650 is a new construction tank code and >650 is up to at least the 10th Edition. If this is a new >tank construction issue, you should comply with the latest >edition of 650. If this is an existing tank, then API 653 >would govern instead of 650. > >Hope this helps! > > >David Hendrix >The Hendrix Group Inc.