SA335 P91 Butt joint welding

By rvraman0 Date 02-21-2017 06:37

I have been welding SA335 P91 pipes of OD 558 and thickness around 80 to 90 mm.Root pass is by Tig process followed by two layers of SMAW welding.I also purge the joint with argon to prevent root oxidation while welding .Subsequently by SubArc Process to complete the welding .After PWHT radiography is taken which does not show any indication .How ever the UT exam shows indications mostly 3 to 10 mm from the root .Before UT grinding is done on the inside of the pipe to smoothen out any excess penetration . What could the the problem and the solution ?

By Joey

Date 02-21-2017 09:25

3"thk using RT? :eek:

Why must use two different NDT method?

Hard to guess, and difficult to pinpoint the problem in your post....there are many many solutions like using UT alone, or replace the welder, or hire a CWI to monitor the welding, get a welding consultant, buy the exact lenght of pipe without the need to weld etc etc.

By js55

Date 02-21-2017 21:31

I'm guessing you are using cobalt for RT given that thickness. It will not provide the resolution of other sources with thinner walls. Your indications are most likely lack of fusion in which the plane of the fusion is perpendicular to the source.