🚀 go-pugleaf

Susan,
        I forwarded your question to my local welding instructor, Latham
Mortensen.  He brought me a book to read.  The book is Welding Handbook,
Volume one, seventh edition.  It has a short section on how magnetic
fields affect welding arcs.  Probably other welding books do also.  The
actual fields and effects are undoubtly quite complicated, but I did get
some general information from Latham.
        It is true that oil well pipe is magnetized.  The magnetic fields
involved in the welding process can cause a deflection of the arc called
"arc blow."   Adjustments may need to be made in the welding technique or
setup in order to keep the puddle in its proper place.  (Not only will
the molten metal spatter, it may just move away from the joint being
joined.)  Changing the
position of the arc and rod, changing the location of the ground clamp,
or running the cables over or around the pipe in certain locations may
change the magnetic fields enough to improve the situation.  According to
Mort you just have to play around with the setup until something works.
        If your friend has the ability to weld with AC instead of DC,
that may also help.
        Even without magnetized pipe you are always faced with possible
interactions between the field produced by the arc current and that
produced by the current in the cables and in the metal being welded.  You
may also have eddy currents in the metal.
        This is by no means an adequate explanation for a true physicist,
but it does verify that there is some interesting physics going on here.
It illustrates that physics has applications in everyday situations in
many more ways than most of us ever think about.

Thanks for a stimulating question.

Everett Hinton
Central Community college
Hastings, Nebraska