Re: Vessels not failing in hydro test

From: <Christopher>
Date: Mon Aug 29 2005 - 10:22:00 EDT

On Aug 29, 2005, at 3:35 AM, Tomy John wrote:

> 1. Why vessels are not failing in hydro Test, where the pressure is
> 1.5 times the design pressure.Becauce t=PD/(2*Str)(Hoop stress).
The allowable stress at maximum allowable pressure is lesser of 2/3 the yield stress or the ultimate stress/3.5. (ASME Code Div 1). The proof factor isn't 1.5 any more but 1.3, so the hoop stress never gets to the yield value during hydro-test. There's also a 15% margin (roughly) between the actual yield strength and the statistical minimum which is specified for design. And it's a practical impossibility for vessels to be designed with the wall thickness precisely equal to the minimum required value for the few materials where the yield strength governs the design allowable.
Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=I_jHBJ2f9eaV-PJf10zmzjZnP2a7OcybkggBtnfDNsftV_nTP0tKLeP3YHupr6D9-IGnsJqNdf9Yvxl3">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 Mon Aug 29 10:22:00 2005