longitudinal weld flash

I am looking for information on the allowable flash which can remain on the longitudinal seam of welded pipe for both the ID and OD of the pipe. Can anyone help?

Our company designs piping systems for molten polymer flow for fiber extrusion (dental floss, carpet fiber, the little red and blue thread in US paper money...). Deformities in ID's of the pipe can potentially create dead spots leading to the degradation of the polymer (burnt polymer). These can break free and cause defects or breaks in the thread line. We typically buy seamless pipe but this particullar application requires us to us a Hastelloy material which we can only find in welded pipe.

The problem is not the butt weld of joints and flanges. The problem, I think, is the longitudinal weld of welded pipe itself. The pipe runs can be many feet long so any honeing or machining along the axial length is not an option. There must be a ASME/ASTM spec for the alowable tolerance of the flash weld produced when making welded seamed pipe.