Knife edge flanges in PV?

[HDS]

I have been designing vacuum vessels for a while and am started to work on some pressure vessels. In vacuum systems flanges with metal gaskets and knife edges to dig into the gaskets are common. The conflat is the most popular one (

http://www.lesker.com/newweb/flanges/flanges_technicalnotes_conflat_1.cfm?pgid=0).

I have seen several pressure vessel flanges with metal gaskets. However, I haven't seen any flanges in the pressure vessel catalogs with knife edges.

I there is problem with the knife edges in pressure flanges? I have some theory about the risk of small imperfection in the knife edge or sensitivity to flexing of the flange. However, I would like to find out from you the real reasons they are not used. What would the failure mechanism be?

(I have read the other threads on ENG-tips about this but didn't find an answer.)

 

[HDS]

I should mention that I have seen PV gaskets with knife edges but no flanges.