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Hollow Bead Defect

Hollow Bead Defect

Hollow Bead Defect


Can someone spare their precious time in answering my below question please ?

Well, we are constructing a 10" Water Pipeline using API-1104 as acceptance criteria.  We are applying a dolly-mix procedure (Root-uphill with E7010 electrodes and rest downhill with E7010 electrodes). Pipe W.T is 9.27mm.  This dolly-mix procedure is due to the pipe ovality problems to avoid the lack of root fusion and root undercut defects.

While interpreting films, we have found an hollow bead defect in the root pass.  our client is telling that hollow bead will not occur when applying uphill root progression welding.

Can someone explain this statement is correct or incorrect with reasons please.

Thanks in advance.

RE: Hollow Bead Defect

Normally the 7010 for the root would be downhand using a drag technique (DC+).

The following is a very general statement and all may not agree. This is based on research done in Au.

Problems with hollow beads begin in the root pass when the primary causes, very high welding currents and travel speed are used. One additional contributor is the high cellulose electrode such as your 7010.

Here is a paper where this was presented.

Cantin D., Bee J., The causes and control of hollow bead in pipeline girth welds WTIA/APIA
Research Seminar, Wollongong, NSW Australia 26 October 1995

RE: Hollow Bead Defect

Thank you unclesyd. As you said E7010 for the root would normally be downhand. But since we had applied an uphill root pregression, travel speed would not be that high. Hence, are there possiblities for Hollow Bead to occur in root pass?

Thanks for your time.

RE: Hollow Bead Defect

I've seen it going both ways and checking with some RT technicians they all said they have seen it with either process.
There are secondary conditions that can contribute to the hollow bead defects. One of more prevalent contributors is running (DC +) where there are several papers that state that (DC -) will help prevent same. In V-up some welders tend to take the squeeze off the electrode if using the drag technique. Long arcs with relatively high amperage is supposed to be a prelude to form hollow beads.
At times it can be hard to pin down the exact cause as the biggest variable is the welder.
I've seen it most when a welder has been gigged for wagon tracks and turns up the heat to overcome this problem.


RE: Hollow Bead Defect

Thank you unclesyd. Finally i got the answer from you.

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