RE: Thick and High Pressure Pipe

From: <Christopher>
Date: Thu Jun 21 2001 - 12:06:00 EDT

>The two are almost alike with one signifcant
>difference - the factor of safety. The Power Piping uses 3:1 and the
>Process Piping uses 4:1. What does it mean -?, the b31.1 will require a much
>thicker pipe sched than those of b31.3. thicker pipe cost money.
If the factor of safety is different the codes are different--they don't overlap, just like Section III and Section VIII Div 1 don't overlap.

Just for cultural value the Code allowable stress of UTS/4 isn't the same as a safety factor of 4. The actual burst pressure of a cylindrical shell is about 3 times the pressure needed to stress the shell to the allowable value. Properly built pressure vessels eventually fail from fatigue at stress concentrations like nozzles, not by bursting. The actual margin against fatigue failure is 1.3 to 1.5 for infinite life, higher for smaller numbers of cycles.

Christopher Wright P.E. |"They couldn't hit an elephant from <a href="/group/PipingDesign/post?postID=vM6PT6BwuYXGWceknCnThL61gCWFtpmp3eymgidfUVrsqHCWU5a8xNKQRytlUGcXBXMIgXjppgbN-puY">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 Thu Jun 21 12:06:00 2001