We want to heat the high pressure hydrogen gas up to 150 degree centigrade in a heat exchanger by using available thermic fluid of sytherm oil T-55
Charles Law states: That the volume of a fixed mass of gas held at a constant pressure varies directly with the absolute temperature. If you increase temperature you'll increase pressure.......
Are you asking what will happen if there is a leak in a heat exchanger with hydrogen gas on one side and hot oil on the other? Without a great deal of detail about the heat exchanger design and the two systems it is connected to there is little that can be said. In the first place you have used a general term high pressure that means different things to different people. There are many vapor and hot oil exchange systems in operation all over the world. Based on my personal experience, if you want a guess then my guess is there will be an over pressure of the heat exchanger and the connected oil piping system that might well result in a rupture of some component unless the pressure relieving system is properly designed.
