Re: Removal of gaskets after pressure test of piping system.

From: <Christopher>
Date: Tue Sep 06 2005 - 11:17:00 EDT

> The hydro test is for checking the soundness of the
> fabrication, not for the efficiency of the joint.
If you'll think about it, a test to 1.3 times the maximum allowable working pressure isn't a very good test, since ASME Code vessels has a margin of failure against bursting of about 3. Only the grossest construction or design flaws will show up in such a test. It happens from time to time, and the cause usually turns out to be some horrible blunder that should have been caught in the shop or design office. In fact most vessels fail from abuse, fatigue or environmental factors, not design flaws.

I was told one time a while back by a Code veteran on a committee I worked with, that the vessel hydrotest is actually a leak test and the proof factor (1.5 at the time) was set to make sure that riveted joints wouldn't leak. These days you might be able to pick up pinhole leads in welds or gross distortion leading to a leak, but you don't really learn anything about the vessel construction unless it bursts. That said, I think a hydro-test to 1.3 MAWP is a good idea, but it has about the same diagnostic value as kicking the tires or slamming the doors on a car you're about to buy.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=TDzNO6V9hY9HZpR11Tjb9RP7aPzbjBKYHRquXgs1DxBIfe9x4-iV9YkNIBPppxYlEx56ctfWn-HtPW8WEzk">chrisw@skypoint.com</a> | this distance" (last words of Gen.

.......................................| John Sedgwick, Spotsylvania

1864)
<a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a> Received on Tue Sep 06 11:17:00 2005