The National Certified Pipe Welding Bureau (NCPWB) has released a new Technical Bulletin that explains the origins of the 37-1/2°± 2-1/2° bevel, the normal bevel angle found on piping fittings and flanges and in many specifications and standards.
New NCPWB Technical Bulletin Explains the Origins of the 37-1/2 Bevel

show-title=”true”