Stainless RTJ w/ Stainless Gasket - Relative Hardness

[ConstantEffort]

A client wishes to use RTJ on CL900 systems in both 304SS and 316SS. The gaskets are to match the metallurgy of the line, so I've got two 304SS flanges squeezing a 304SS gasket. Ditto for 316.

My concerns are...

Will this situation produce a satisfactory seal at reasonable bolt loadings?
Will the flange continue to function if the joint has to be broken and remade with new gaskets?​

304SS and 316SS ring gaskets apparently are available at a max hardness of Rockwell-B 83 or Brinnell 160. (

http://www.sealing.com/fileadmin/docs/Ring_Joint_Handbook.pdf)

ASTM A182 does not directly control hardness on F304 or F316. ASME B16.5 is no help on hardness either.

My limited understanding of gasket sealing is that the soft gasket should plastically deform to meet the hard, rigid flange which only deforms elastically. So in this case it seems that the plastic deformation may be shared between the gasket and the flanges.

Anyone have other recommendations for the situation? The 304SS line is operating at -200F and the 316SS is in corrosive services (rich amines, condensing H2S, condensing H2CO3).

 

[LittleInch]

I'm with you on this one - the ring should deform not the flange surface. B16.5 though then refers to B16.20, which I don't have a copy of. What does that say?

I have seen it in piping specs that hardness needs to be a certain number below the flanges, but can't recall by how much.

Probably best to find a technical agent in your ring supplier and get their advice. They've seen it many more times than you or I.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MickMc]

Previous Project had 18/8 Stainless Steel RTJ gasket as a maximum brinell hardness of 135 with ring hardness being a minimum of 15 HB less than flange hardness.

 

[SNORGY]

I'm with MickMc and LittleInch. I have had "superiors" in the past - both on the EPC side and on the Producer (Client) side - who would get irritated with me and tell me, "It doesn't matter.". They even wanted me to write it *out* of the Specifications, a request I have always ignored. I always ask for 20 HB or more softer in the gasket than the flange. If it takes Procurement a bit longer to find it from suppliers because "the spec is tight", well, so be it. I also think MickMc's recommendation for materials in this instance is reasonable.