In general PWHT is only required for carbon steel material if the weld thickness>38mm .
In between 32 and 38 mm of weld thickness if u maintain a preheat of 95C u dont need any PWHT for Pno1 materials.
Every organization has their own procedure for PWHT that stays within the restrictions of UW-40 of ASME section 8 div1.
For example one company has a procedure for PWHT like this.
Rate of heating-100c/hr max
U can’t go beyond 222c/hr on heating rate and 280c/hr on cooling but u can use the temp range within this limits.
And rate of heating and cooling shall not lower than 55c/hr.