I work in a large oil refinery and am not aware of any applications requiring a metal-to-metal seal without the use of some sealant. Are you asking for a pure, dry, metal-to-metal seal with no sealant compound applied? It might be best if you describe the application in order to get replies from people familiar with that service.
With that said, we seal metal-to-metal joints with no gasket in water (up to 3,600 psi), steam (up to 600 psi) and lube oil (generally low pressure). But, all of these use a sealant and often use a joint design that makes the sealant less necessary. For our highest pressure applications, (water at 3,600 psi), the joint consists of a cast carbon steel head bolted to a cast carbon steel case that has the sealing surface overlaid with 309 SS. The bolting on the joint is designed to result in stress beyond yield in the SS overlay. Even then, we coat the surface with triple boiled linseed oil or a non-hardening sealant like Permatex or Copaltite. Some would argue that the sealant in this application is really used as a lubricant. But, we have no requirements for surface finish in this joint and it has never leaked a drop despite being disassembled over 20 times during the past 60 years.
Steam turbines often use joints with no gaskets on the case joints, governor valve to case, nozzle ring mounting, etc. But, once again, a sealant is applied. This is typically a hardening sealant, but some use non-hardening compounds like triple boiled linseed oil.
The case split line on a large multi-stage centrifugal compressor is also metal-to-metal with no gasket. But, they use a hardening sealant like RTV and deliberately leave a slight cross-hatch pattern on the faces to grip the sealant. Even then, it is common to perform a contact pattern check to make sure of full contact between the mating surfaces. Contact is more important than surface finish in some applications.
So, basically, the design of the joint and the use of an appropriate sealant are probably more important than the surface finish in the range you are describing. Additional information will yield more useful responses.
This forum might not be the best place for your question.
Johnny Pellin
