1) Root Gap Tolerance is an non-essential variable and shall; comply with the WPS. Normal Root Gap used is 2.4mm +/- 0.8mm and it depends on factors like Thickness, size of Filler wire used for root pass, welder's skill and no restriction as per ASME B 31.3.
2. Offset or misalignment as per WPS as specified in the client specification and B31.3 only recommends for Tapering for unequal thicknesses or diameter.
3. Bevel angle for steel as recommended below but may vary for Materials based on their thermal conductivity
ASME B31.3 normally references ASME B16.25 for bevels
Thanks & Regards
J.Gerald Jayakumar