pressure and temperature

[EngineerPhil]

Perhaps I am missing something.

I'm redesigning a PV to take a MAWP of 14.5k psi and be little less than 10 liters in internal volume. The medium is hydraulic oil with a max temp of 300°C.

If I want to test at this 14.5k psi at a temperature of 200°C, what should I consider in terms of design?

The obvious are hydrogen embrittlement (but I want to use a low carbon steel, P110 to be exact. This is similar to AISI 4145 in properties), creep and thermal stresses. But how do I go about calculating these? Are there more that I have missed?

Is it ok to utilise the gas laws to design the pressure vessel such that at 200°C I do not exceed the 14.5k psi pressure? My thermodynamic theory is failing me.

In practice the vessel will be held at relatively low pressure of 2k psi whilct the oil is heated, then when stabilised (pressure will increase slightly and level off) the test pressure is then achieved at 200°C (typically 80% of the MAWP). Will the temperature have any real effect as the pressure obtained is that at temperature and not equivalent to that at ambient. Does that make sense? It is a pressure but not a constant volume due to the additional volume pumped through to raise the pressure.

Well I'm confused .....

Hope to hear some clever thoughts soon,

BR

Phil.

 

[deanc]

What Code are you building to? If this is welded,suggest you consult a good welding eng.

 

[EngineerPhil]

Deanc,

Not building to any code. This is a vessel to test parts at temperature and under pressure. I am using a general non descriptive guide as I am not manufacturing the vessel for commercial purposes and am working within the pressure directive (UK) which allows "safe engineering practice" as long as the max pressure and fluid volume is 1000 bar and 10 litres.

The design is a flat capped cylinder and I am going to have threaded flanges put on.

Hope this helps to clear things up?

Phil.