My Client is expecting mechanical damages on the internal surface of vessel shell (suction drum) which is in service. We are required to prepare for repairing unexpected vessel shell damages during upcoming plant shutdown. The vessel shell material is SA 516 Gr.70N, shell thickness is 71mm, design MDMT is -37 deg. C & service is non-lethal. The vessel was originally PWHT'd per ASME Sec. VIII Div.1 (due to weld deposit thickness in excess of 38mm). Impact testing is also required.
We were required by the Client to follow the stringent requirements of NB-23 & API 510 while repairing the vessel. Both NB-23 & API 510 call for alternative welding method, viz. controlled deposition method, when PWHT & imapct test are required by the original code of construction. However, we proposed WPS for repair using normal welding technique instead of temper bead welding (TBW) method with the following justifications:
1. Repair depths are not expected to be more than 38mm.
2. Weld build up can be carried out by ordinary welding technique instead of TBW method since PWHT is not required until 38mm weld deposit thickness as per ASME Sec. VIII Sec.1 (UCS-56). Both repair codes (NB-23 / API 510) refer to original code of construction for PWHT requirements.
Kindly confirm if our justifications are valid for repair welding without TBW method applying NB-23 / API 510 stringent requirements. Note that R-stamp is also required after repair.