Para 3.7.4 calls for Thermal Stress Relief i.e. PWHT (as per note of para 3.7.3). Please comment for requirement or no-requirement of PWHT for shell plate to shell plate vertical and horizontal welds having metal thickness greater than & equal to 3/4" for Carbon Steel standard Plate MOC

Debasis I do not have the latest API 650 standard to refer and clarify your doubts. My information may be outdated and may not be latest code rules if the API code had been upgraded to reduce to 0.75" thickness onwwards. Para 3.7.4 - you are referring - for PWHT for Group I, II, III or III A speficies that shell plate exceeding 1" thickness - whether it is branch connection, whether shell to shell plate connection requires PWHT except for flange to neck or man-way neck attachments provided the weld is outside the reinforcement. Since your question is related to Group I / II (Carbon Steel material), i guess, you can safely assume that 3/4" thickness is probably may not come and could be exempt from PWHT criteria provided enough pre-heat is applied and the weld is allowed to cool not too rapidly after welding. Please note that my information, posted here , is not on latest API 650 requirements. If API had revised to reduce the thickness to 3/4" (0.75") you have to adhere to this requirement of PWHT for any joint of thickness 0.75" (3/4") - shell to shell plate bottom weld joints (vertical and horizontal).for PWHT. Please note that the same will change when applied to Group IV, IV A, V or VI for opening connections or reinforcement and the strict need to do PWHT even at 0.5" (1/2") thickness. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India July 16 E-amil: nishi@vsnl.com >Para 3.7.4 calls for Thermal Stress Relief i.e. PWHT (as per >note of para 3.7.3). >Please comment for requirement or no-requirement of PWHT for >shell plate to shell plate vertical and horizontal welds >having metal thickness greater than & equal to 3/4" for >Carbon Steel standard Plate MOC

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.