Regarding fabrication tolerances, the main ones -diameter, out of roundness, welds misalignment etc.- are specified by the Code.
Other tolarances should be stated by the end user or the project engineering firm that he appointed as consultant. Two examples are the leveling tolerance of the trays supporting rings, because the out of level of the trays will interfere with its operation, and the out of squareness of the nozzles.
I've got the Allowable Tolerances for Pressure Vessels issued by The M. W. Kellogg Co., which is (or at least was) one of the best project engineering firms in the world in the oil and petrochemical fields. It's not in electronic format, so I should make a copy and send it to you by air mail. It'll take 12 - 15 days to reach you, considering that we're 180ยบ apart on the Earth sphere. Before, however, you must let me know your mailing address.
Giovanni S. Crisi
Sao Paulo - Brazil