"If you do impact testing in which direction, in which end of the pipe, each pipe, each elbow, is the pipe long welded? Absolutely too risky for me."

Me too.... thats why I put my two cents in as I did. I would be amazed to find any high tensile carbon steel that would meet the impact test requirements of B31.3-2004 Chpt III

Mr. Lee has looked at this problem soley from the standpoint of needing a thermal expansion coefficient without thinking of the notch toughness brittle fracture consequences.