Some gaskets specified in mechanical design is very expensive and I'm looking for a low cost solution for gaskets to be used in ordinary hydrotest for ASME VIII div 1 vessels. Could I use a gasket, different from that specified in mechanical design, only to perform the Hydrotest. only comment with this is that I have seen a very soft (forgiving)gasket used for hydro and it does not leak but when the unit is placed in service with a harder gasket the unit does leak. This is more of a case with specially fabricated flanges (in the case I am referencing it was fabricated rectangular flanges) where the surfaces were not machined properly and the softer gasket conformed to the irregularities and the required service gasket did not. Typically, I specify that the hydrotest gaskets be equalivent to the services gaskets, especially when fabricated flanges are used (in addition to make sure there is proper tolerancing on the flange). While this can be perceived as expensive it really isn't when you are on a shutdown replacing a piece of equiment and you are starting back-up and the connection/attachment point starts leaking.

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