Re: presure drop during hydrotest

From: <Christopher>
Date: Fri May 12 2006 - 12:39:00 EDT

On May 11, 2006, at 10:31 PM, Wutt wrote:

> Any calculation to support my hydrotest.
> The pressure is drop according to temperature, I want to use the
> calculation to prove to client that this is not cause of leak.
The material inside the vessel changes with temperature according to the principles of thermal expansion = CTE x length x (temperature change). So does the vessel itself. If the volume change of the contents is different than the volume change of the vessel, the pressure changes. Note that the volume change of the vessel (say a cylinder) is found from the relationship between volume, diameter and length: V = piD^2L/4 delV = pi (2D delV +delL)/4 del L and del D are the changes in vessel geometry from thermal expansion del L = CTE x L x temperature change. The volme chance of the contents, presumably water is the bulk coefficient of expansion x volume x temperature difference.

If you were doing this for me I'd also want you to prove to me what the actual temperature change of the vessel is. It won't be the same as the ambient temperature change because the vessel changes temperature much more slowly than the surrounding air. You'll have to do a heat transfer calculation to estimate that. A measurement of the tank wall will help, but it won't telll you the whole story.
Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=Kh_ejSXrbuBw5BAssgtGS5eShKFr6M-eLMiYxPgrupLiJYRokJaCGuFCx2KDo_zUUh_42vcNKwlSCvsyrA">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 Fri May 12 12:39:00 2006