Welding and Magnetism

[cacofes]

On a recent pipeline cut out operation, our welders found some magnetism in the line. This is a 12in 70 km long dry gas pipeline. From what we saw, there was no magnetism previous to cutting the line but once we cut it, it was magnetized. There are many theories about the source of the magnetism but one we want to discard is that it could have been produced by the pneumatic cutters we used. Has anyone experienced magnetism from pneumatic pipeline cutters?

 

[EdStainless]

You can only see the magnetic field effects at a transition, such as an end. The line didn't change in magnetic field, the cut became a place to see its effect.
Any long piece of steel will have a magnetic field, because the earth has one.

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Plymouth Tube

 

[stanweld]

Does the pipeline run east/west. Telluric magnetic fields are commonly induced in such pipelines.

 

[TTT]

Not unheard of. In remote sites it is possible to demag the local area sufficiently for welding by wrapping the welder leads around the pipe ajacent to the weld. Switch to AC, and make several welds (on scrap), each time reducing the ampage. Sometimes it works enough to stop the weld rod being attracted to the parent metal.

 

[metengr]

There are many theories about the source of the magnetism but one we want to discard is that it could have been produced by the pneumatic cutters we used. Has anyone experienced magnetism from pneumatic pipeline cutters?

You can discard magnetism from using pneumatic pipe cutters.

 

[brimmer]

Very common... ever run an MFL tool in the line?