GJ:
that one trick i like to use but most area it is banned pratice for safety reason in case stray current get to somewhere else and do wonderfull damage. few years ago i ran 350 amp thru the frozen pipe and a bit of stray current went to next building and got the ground rod over heated almost point to start to burn the wood off.
air commpressor do pretty good trick once you get the air flow thru my most common trick is used my truck exhaust it is hot engough to thaw out the pipes and alot of gunk fly out on oppostion end.
honestly i try to rember what link or source saying about welder on frozen pipe is big no-no.
merci , Marc
