Hello all,

One of the frequently asked (and not always completely answered) questions in this forum concerns how much variation from the designed (and analyzed) system is allowed in the "as built" system. It would be good if a recognized agency would make a statement on how much variation from the design is allowed.

My answer has always be to reference the WRC document "Technical Position on Piping Installation Tolerances", Welding Research Council Bulletin 316, July 1986 and also the EPRI document "Guidance for Piping System Reconciliation", NCIG-05, Electric Power Research Institute, EPRI-5639, May 1988. I think one of these documents even has guidance on how many changes in direction there must be between existing piping and the system you analyze to assure that you can "declare" a "virtual anchor".

A colleague pointed out to me today that some of the information from one of these two documents has made it into the ASME B&PV Code and resides in Section III, Nonmandatory Appendix T, Article T-1000, "Recommended Tolerances for Reconciliation of Piping Systems". Sadly there is no mention of "virtual anchors".

I hope this information is useful to someone.

Regards, John.