Hi,

We need a socket weld of a 1.5" pipe into a casing.  According to Figure UW-16.1 (t), I need an undercut for the fillet weld if I have a slip fit.  Because a very old drawing called for it, we NPT tapped this port.  So we will be threading and socket welding.  Is this acceptable, I can't find any language regarding this type of connection in VIII?  Furthermore, are there separate requirements for a threaded and welded connection vs a slip fit connection? 

I see there is a requirement spacing below a slip fit (1/16") connection.  Is this gap for temperature growth?  Room for any gases during welding to escape?  Will a threaded connection cause problems with welding?

Thanks and cheers,