Copper gasket.

Even the nonstandard solution is being adapted and in most cases the site personnel do violate the codes and standards to find some solutions specifically without even consulting the engg. office.

So I go by what Bhattaji says as, it does pose serious hazard being a 1500# rating and with a gas service. A big potential for a high speed accident. The reasoning for this is simple. The B16.5 flanges does increase in the OD and thickness of the flange and the hub as the size increases and does have the backing for those dimensions under those Max. Working Pressures. Already it is a weak point in a piping system and if you are prescribing a flange dimensioned for 2" and going to use as a 2.5" connection, moreover a bored flange without a hub, which makes it the most weakest point. A 6mm fillet weld cannot substitute a hub.

So use of SPW / copper gasket can be at the descretion of site and if from engg. office it is to be replaced with a 2.5" reducing flange. As Bhatta refered the bore dim., which is a purchased defined parameter and the para 6.8 very well says that the hub will be as per 2" and thk/od as per 2.5". So I do not find any problem in going for it.

Sometimes such decision is like being with angel / devil.

With regard to your other query, in ethylene plant copper is used only in some cold fraction part and not as a flat gasket but as a V groove O-ring gasket. Aluminium and copper are also used in air seperation units . The torquing calc is the standard procedure and same as the ring joints. But I remember some posting was there by Raghuram some time back on the subject. Pl. check the group's archive.

You can also check http://www.futek.com/boltcalc.aspx

With regards,
Kannan



Thanks Kannan,

 
Kannan, please ignor questions in earlier mail.  
As you said the comparision of diameters was done and we were able to eleminate most of the cases which were originally thought to be problematic.  On most of the cases comparing the gaskets ID and instrument tube OD, it was found that standard 16.20 spiral wound gasket can be used.  So the problem was reduced down to small numbers.
 
As you have said that standard SPW gasket torquing cannot be used for copper gaskets.  Is there any reference to calculate the required torque?
 
regards
yogesh