Best practice for bead sequencing on large diameter steel pipe using mechanized GMAW-P?

by J. Russell
(Iowa)

I'm having difficulty qualifying a procedure using GMAW-RMD (Miller short circuit process - not the problem) followed by filling the joint with GMAW-Pulse (the problem).

Here are the finer details:
1. 18"OD pipe, 3/4"thick, steel SA106 B
2. ER70S-6 filler
3. qualified to ASME Section IX
4. V-groove
5. Miller Axcess 450 power source
6. mechanized process
7. single pass GMAW-RMD root (great)
8. fill/cover passes using GMAW-P (fails radiograph)

Our company requires radiograph examination of all of our qualifications and of course we're having a hard time getting our GMAW-P passes to pass radiograph. We get lines of lack-of-fusion mostly on the side walls but also sometimes in the middle between passes as well. I've attempted oscillation to make our bead profile flatter (so we don't get harsh valleys in the weld) and attempting some dramatic torch angles to keep us ahead of our puddle but with no avail.

Any suggestions?

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My first impression is that you should position the torch at a position where the welding is slightly uphill...like 11 o clock with a 90 degree torch angle ...or slight push angle...as well as torch oscillation to flatten the bead profile.