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. Otherwisein a broader sense turbine casings are also pressure retaining components.
If I design a steam turbine casing as per ASME code, whether it will be overdesigned or should I increase the factor of safety to get the allowable stresses?
Steam turbine design is based on creep, fracture and fatigue of high temperature components, along with theory of vibrations, while design of pressure vessel is based on the value of steam pressure,that vessel is subjected to as per ISO-R831 and ASME codes.
Ref>Creep and Fracture in High Temperature Components: Design and Life ...
edited by I. A. Shibli, S. R. Holdsworth, G. Merckling
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ASME BPVC is predominantly related to design and fabrication of pressure vessels . Although turbine is mechanically important aspect it can not be considered vessel.
There might be three reasons to provide higher safety factors.
1. Rotating component
2. Vibration
3. More wear and tear
Hope you got answer.
subjected to centrifugal stress ,tension defects crack associated with high temp fatigue creep makes it liable to fail
thanks to all of you for your responses.....will wait for some more...
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