Re: Maximum Gasket Seating Stress

From: <Christopher>
Date: Thu Dec 01 2005 - 10:20:00 EST

On Nov 30, 2005, at 11:30 PM, HPRAJAPATI@ltcis.ltindia.com wrote:

> Can anyone tell me what is the maximum seating stress for Ring Type
> Gasket
> ( Octagonal ring ) having SS soft iron with BHN 90 ?
You need to do a quick estimate of the average compressive stress in your particular gasket detail from the gasket load and the cross-sectional area. You get the gasket load, Hg, from the flange calculation arithmetic for different bolt loads and you can estimate the cross-sectional area from the gasket detail you're using in Code table 2-5.2.

The hooker is mechanical properties for the gasket. A BHN of 90 is pretty damn soft, and there's no way to figure the compressive yield stress for the BHN anyway. The correlation for tensile strength [UTS = 515(BHN)] is approximate at best and probably not even close for such soft materials. The compressive strength of iron is much different than the tensile strength. If you're really serious about this you should probably do a compressive test on the gasket installed as it would be in the field.

The underlying question you need to ask yourself is whether overloading the gasket will damage the flange or compromise the seal. If you damage the gasket you may get it to seal for a while, but after a couple of load cycles everything shifts and the gasket can't accommodate the movement and it starts leaking. The smart thing to do is fix the flange installation so you don't need to crank down on the bolts.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=GkkxEs_KkBSVBpLII0S1HKEfgG66Ixt9HgjexFRkZGpMsAuU_8ECvlmwagRzPBF3-edJ7UcuWmCk">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 Dec 01 10:20:00 2005