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Category: Equipment Design
Question: If the incorrect design pressure was stamped on a shell and tube heat exchanger by the fabricator, is it necessary to repeat the hydrotest to have the nameplate corrected?
Keywords: v1i10,shell,tube,heat,exchanger,rating,rerating,wrong,design,pressure,asme
Answer: BACKGROUNDThe heat exchanger in this case was stamped for 115 psig/FV on the tube side and 150 psig/FV on the shell side. The unit was tested at 195 psig on both sides by the fabricator (which corresponds to the required 1.3 times design pressure needed for ASME code). The 115 psig rating the tubes was in error and it should have been stamped for 150 psig/FV as requested by the buyer and per the testing pressure that was actually used in the shop. This heat exchanger has never been in service.ANSWERThe fabricator in this case is most likely protecting their interest. The have two pieces of information (the name plate design pressure for the tubeside and the hydrotest datasheet for the tubeside). In this case, for them to simply restamp the unit, they would have to be 100% certain that the mistake was made on the nameplate and not of the testing report. ASME Code section U-2 and UG-90 will help with this topic, however, this is a matter of safety and procedure. There's most likely no way to know for absolute certain that the tubes were tested at 195 psig with the conflicting nameplate. It would prudent course to allow the fabricator to retest and then restamp the unit. This will ensure the safety of the personnel responsible for working near this unit. Additional, it may be good idea to audit the fabricators quality system if you're to continue to conduct business with them as this is a mistake that should not happen again.Reference: Mr. Phil Leckner, First Content Manager, CERP