Centrifugal Pump Nozzle Loads Verification

[Boghi1990]

Hi,

Are centrifugal pump nozzle loads solved for the operating temperature or are they solved for the design temperature? In my piping stress model I have defined the design parameters as T1 & P1, and the operatin parameters as T2 & P2. The pump is a centrifugal In-Line Vertical pump. Any suggestions are appreciated.

Regards,

One Point

 

[C2it]

It depends upon the definition of design temperature. In some companies it is the real max operating, others add a constant value like 30 deg C to the max op.

So far as pump loads, or for that matter loads applied to any connected equipment is concerned, you need the realistic worst coincident temperature and pressure combination that the pump will be exposed to. The equipment manufacturer should have designed to the same loads. Remember that it is quite acceptable FOR NOZZLE LOADS (and support/restraint loads) ONLY, to use the hot Young's modulus in a pipe stress calc.

 

[StevenHPerry]

Remember that it is quite acceptable FOR NOZZLE LOADS (and support/restraint loads) ONLY, to use the hot Young's modulus in a pipe stress calc.

Acceptable to who and on what basis?

 

[C2it]

Steven, Acceptable to the realms of common sense. The hot modulus corresponds structurally to a high temperature which is going to cause expansion loads. The intent of a mathematical model is to represent reality as closely as possible. If a reduction of maybe 20% in calculated loads is possible in this way, meaning perhaps that a re-route or additional restraint is not required, then do it. That is intelligent and efficient engineering.

The use of cold modulus regardless of temperature is specifically required in the B31 and similar codes and is well documented. It relates to stresses alone. It may be convenient to use the cold modulus only to simplify a stress calc, but it may also be hugely over-conservative with regard to thermal loads.

Perhaps turn the argument on its head .... Say you are designing a turbo-expander for an FCC plant, operating at 750 deg C. When considering casing stiffness, blade clearance and shaft alignment, would you use the hot or cold modulus ? Q.E.D.

For good form I always include a statement clarifying use of the hot modulus in any project stress analysis procedure, which will of course be Client approved.

 

[StevenHPerry]

I'll retract the question. I've been away from B31 too long, sorry!

B31.1 explicitly shows that E_h should be applied for reaction load calculations. Should have looked before I lept.