I was told today that this guy has a friend that works for the pipeline and he tells me that he can weld high pressure line with a thickness of 2-5" with a tig. Why would this need to be done? All the pipeline guys I know use Arc welding on the pipelines so I am just asking to see if this is tr...

With both tig and mig welds, if both are done correctly on the same material which is stronger or are they equally as strong and why? What do you think?