Re: [PipingDesign] Regarding stress check for hydro test

From: <Christopher>
Date: Thu Jan 17 2008 - 18:55:00 EST

On Jan 17, 2008, at 6:26 AM, M. Engineer wrote:
> The test pressure producing hoop stress of 90% of SMYS
> is for newly constructed in-plant piping.
I've seen this before on the list and it really seems like a high proof factor. It isn't uncommon to have local secondary stresses that exceed the hoop stress by 50% or more. Testing the a hoop stress level of 90% of Sy will cause visible distortion in some areas, which n turn is grounds for rejecting a vessel during a shop hydro. Much more important is the possibility of extending a sharp defect like a weld crack to the point where the vessel or pipe run ruptures during the test. Or you might extend the crack to the point where subsequent stress cycles ultimately brings about a fracture. I've been through this a couple of times, and it really could spoil your whole afternoon.

> There are
> several

Christopher Wright P.E. |"They couldn't hit an elephant at chrisw@skypoint.com | this distance" (last words of Gen.

.......................................| John Sedgwick, Spotsylvania
1864)
http://www.skypoint.com/~chrisw/ Received on Thu Jan 17 18:55:00 2008

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