Our maintenance department wants to weld a ASTM A105, class 150, welded neck flange, std, to a ½ dia, A53, schedule 80 pipe. I have found sound technical reference for joining butt-welding fittings to pipe of equal or lesser wall thickness. However I have not found solid reference for joining a fitting to greater wall thickness. My guys want to bore the ID of the pipe to match the flange. I can’t support that idea because of the post welding hydro test requirement of 1.5 times the operating pressure (225 psi test pressure). This line transfers sarin nerve agent to an incinerator and we would prefer no leaks on the way and a solid connection at the instrument flanges. Our site specification requires class 150, schedule 80 bore, welded neck flanges, on the agent line for sizes ½ to 3 inch diameter but, I’ve been told that there is no such thing as a class 150 schedule 80 bore welded neck flange for ½ inch pipe. My search on the internet for class 150, schedule 80 bore flanges, for ½ inch pipe has not be very productive. How can such a specification be in error for so long? Or haven’t we found the right place for flanges? Its only a few thousands difference why not weld it as is?

Regards Donnie Mann