Steam turbine castings are similar to a high temperature pressure vessel but Para 1.2.4.2 (C) of ASME section VIII div 2 excludes some of the pressure vessels from its scope. which includes steam turbines also. Why so?
As per my understanding failure of boilers/reactors are more safety critical than a steam turbine casing and basic philosophy of design of a component, operating at high temperature, is similar. Only difference that I feel is there is a rotating component inside the steam turbine casing. Otherwise in a broader sense turbine casings are also pressure retaining components.
If I design a steam turbine casing as per ASME code (especially by DBA of section VIII div 2), whether it will be overdesigned or should I increase the factor of safety to get the allowable stresses? Or it is not at all applicable….
I think you will find that this is because steam turbine casings are also subject to thermal fatigue cycling which can give rise to a creep-fatigue mechanism. This introduces additional damage, which is not normally accounted for in simple pressure vessel design. Of course the thing to be careful of is if you increase the factor of safety to reduce the primary stresses this can make the thermal fatigue and creep-fatigue, which are strain controlled worse. You could consider ASME, Section III Div. 1 Sub-Section NH. This is a nuclear code but does consider creep-fatigue. Alternatives are the French RCC-MR or the British R5.
Dear Michael....
Appreciate your response...and it addressed the concern also...
I was searching the answer of this question from a long time and it is the second time I posted it to researchgate....I do not know why but I always missed that section VIII div 2 do not take care of Creep fatigue Interaction (CFI) for that I have to go for NH.
Can you please share some more about "why additional damage introduced by CFI is not accounted in simple pressure vessel design?", Either simple pressure vessel or nuclear - if loadings are similar interaction will happen...Is some conservatism is built in section VIII div 2 design calculations that take care of CFI or it is not at all considered...
Regards
In steam turbine casing the load come from thermal stress as well as pressure (dynamic as and static pressure)
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