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Criteria for choosing lens ring and octagonal ring type gasket

Criteria for choosing lens ring and octagonal ring type gasket

Criteria for choosing lens ring and octagonal ring type gasket

(OP)
Dear All,

In our plant, we are using both lens ring and otagonal ring type of gasket in one pipeline and I am trying to find the reason for the same. The pressure is 340 bar, temperature is 380 deg C, line size is 4 inch

I shall be grateful if you could kindly share the criteria for choosing lens ring type gasket joint compared to octagonal ring type gasket joint. For example, which type of joint is more suitable for accomodating piping bending moments, thermal expansions, variation in pressures etc.

Lookinf forward to your valuable inputs,

Regards,
Ashwani

RE: Criteria for choosing lens ring and octagonal ring type gasket

Hy,

we are also using both types of gaskets, lens rings and RJ.

I think the type of gasket was formerly simply defined by the design standard. As far as I know there is no such thing as a "lens ring" in the ASME standards. Lens rings are still only defined in DIN2696 which was revised the last time in 1999.

From an operational point of view, the lens gaskets advantage is the higher tension on the sealing surface with increasing pressure. Therefore increasing pressure does not lead to as much "force loss" on the sealing surface then it does for other gaskets like RJ.

The RJ gasket is from my experience easier to install (center) and has the advantage of two sealing surfaces, one inside and one outside. It also "pardons" small pits on the sealing surfaces which a lens ring does not foregive.

In general I have made better experience with RJ than with lens rings. Lens rings need to be installed very carefully. Depending on the application, the flange surface needs to be machined everytime the connection is opened.

An additional problem of lens rings ist the plastic deformation if the tightening moment is too high. This would also occur if you have high bending moments at the connection (Which you shouldn't have). Temperature change is from my experience more a problem for pretensioning force than a gasket issue even if you are using different materials for flange and gasket.

What is your experience with lens gaskets? Do you have many leaks after installation?

Regards,
Dan

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