There is no 'requirement'.
There are various codes, roughly divided into structural and pressure equipment. Each has its own rules, based on material, dimensions, ultimate application of the equipment, and other inputs.
We will need much more information to begin to answer this.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
If you thickness of vessel and nozzle reinforcing pad is 20 mm each, you would need a fillet weld of 20 x 0.7 = 14 mm
What should you write on your data sheet??
For shell, there is no PWHT requirement (thickness less than 32 mm) and assuming no hydrogen and lethal service. But the fillet weld size falls in the category of pwht now
What to communicate to your vendor in this case??
If PWHT is mandatory for welded joint of all thicknesses for lethal service (UW-2), how can you avoid fillet welds during PWHT? (Note (b)(3)in Table UCS-56-1)
I could have explained a littel better...PWHT is mandatory for vessel and most exemptions will refer to other parts of UW-2, but some things may not be done prior to PWHT.
Standard Designation: BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description: Section VIII, Division 1 (1998 Edition, 1999 Addenda); UCL-51 and Table UCS-56
Date Issued: 03/22/2000
Record Number: BC00-080
Interpretation Number : VIII-1-98-108
Question(s) and Reply(ies):
Question (1): A pressure vessel is constructed of P-No. 1 and P-No. 8 materials, and is intended for lethal service. The vessel is PWHT. After PWHT, but before performing the hydrotest, the interior of the vessel has a stainless steel lining applied using plug welds. Does Note (2)(c)(5) of Table UCS-56 in Section VIII, Division 1 permit the liner to be applied after the vessel has been PWHT without the need to perform any additional heat treatment?
Reply (1): Yes, provided that the preheat requirements are met.
Question (2): Does UCL-51 permit the liner to be repaired by welding to the P-No. 1 base material after the vessel has been PWHT without the need to perform any additional heat treatment?
Reply (2): Yes, with the acceptance of the Authorized Inspector.