I'm working on a Prototype solid state hydrogen store which was built by some other group last year. My main objective is to analyze its performance. But the problem is this system needs to be leak proof before I can do any performance test. There are couple of issues I would like to discuss in this thread and seek experts advice. Firstly, the main problem is the sealing between cap and the vessel flange. I have used steel gasket but the system fails a pressure test. The gasket seats on a groove. The temp and pressure should be 350C and 15bar respectively inside the vessel. I really need to make it leak proof before doing anything. At this high temp. rubber o ring is unrealistic. Really seeking some expert opinion regarding sealing.