High Pressure Gas - Lapped Joints Connections?

[TEIGRAY]

Hi All,

I've been doing quite a bit of R&D into Lapped Joint Connections and want to utilise some of these for high pressure and high temperature Steam applications.
Most likely up to 50 Bar(g) & 500'C
Reading through the standards for flanges, connections etc its clear that lapped joint flanges can and have been used, all for high pressure systems, some rated to 2500 psi, with the temperature depending on the material but SS 316 should be able to handle this.

My question is why there is little reference for the use of Lapped joint flanged connections with pressurised steam systems,
Most pages and forums etc often cite that lapped joints are only used for low pressure liquid systems. Is there a reason for this that I am missing? Why would lapped joints connections not be used for high pressure gas/steam systems when with the proper dimensions and fitting?
Is it because some lapped flanges are pressed from sheet metal rather than forged?

Kind clarification on this would be great and help me with my research

Many thanks

 

[rconner]

fyi

http://www.eng-tips.com/viewthread.cfm?qid=366161

 

[XL83NL]

This may be a useful article
I'd say LJ's are useful when the material cost is high (e.g. Hastelloy), and the load bearing on the flange is minimal (e.g. a flanges thermowell or pressure transmitter connection). Other than that, if the temperatures are really high with equivalent pressure (i.e. Cl 2500 and beyond), flanged joints should be kept to a minimum to reduce leakage points, especially for LJ's.

/edt; Ive used an LJRF connection for a 725 C/55 barg system for a thermowell connection. Although not the most economical decision as it turned out later (a welded-in TW was even better en cheaper), it worked, as we could skip one WNRF 800HT flange for a 316 LJ flange.