My full real name is Eugene Raymond Walker, and in the name of the King, I hereby lay claim to all mentions of ERW pipe, because it has my initials on it. So there.
Even if all but invisible, the seam is still present. I'm not sure, but I think the weld process is considered 100% efficient, with no reduction in allowable stress. (??)
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In vino veritas; in cervisia carmen; in aqua E. coli.