Pump Nozzle Loads ?

Hi Caesars,

Why Pump nozzle Loads are solved for operating temperature instead of Design temperature as we do for Pressure Vessels.

I think Pumps (Rotating Equipment)are very sensitive to Piping Loads , Which We Should Solve for Design temperature.

Please Throw Some Light on this Topic.

I already Used the search option for this question but i can't get any relavent answers.

Thank u in advance

hi ravanan,

Generally nozzle load shall be verified with operating condition, stress shall be checked with design parameter(EXP.)

rajan

Ravanan,

To expand on Rajan's comments, we use the ambient temperature modulus of elasticity in analysis "runs" to calculate the STRESSES as this is currently required by the B31 Codes. However, when we calculate the loadings (forces and moments) on strain sensitive equipment (e.g., turbines, pumps, vessels) for comparison to the prescribed maximum allowable loadings we use the modulus of elasticity of the piping material at the operating temperature.

With the operating temperature modulus of elasticity (if we are discussing a system where the operating temperature is higher that the ambient temperature) the piping will be more flexible and the loadings on the equipment will be more realistic. In this case if you use the ambient temperature modulus of elasticity in the evaluation of loadings on the strain sensitive equipment your results will generally be conservative.

Note that if we have a system that has an operating temperature that is lower than the ambient temperature we STILL will use the modulus of elasticity of the piping material at the operating temperature for calculating loadings on strain sensitive equipment. In this case, the piping may be LESS flexible and the calculated loadings MAY BE HIGHER than the loadings that would be calculated using the ambient temperature modulus of elasticity - but these loadings will also be more realistic loadings. In this case if you use the ambient temperature modulus of elasticity in the evaluation of loadings on the strain sensitive equipment your results will be neither conservative nor realistic.

Regards, John

I answered a question but it just was not the one that was asked. Another case of me posting before I have had my morning cuppa. I TOTALLY missed the point until I read Ed's reply below and reread the original question. Oh well, .....and the olde guy toddles off for his afternoon nap - nice sunny day today in Trinidad (for a change)!!!

JB

Sara,

It really comes down to how your "design" temperature is defined. For many companies, the "design" temperature, which is used primarily for wall thickness calcs along with the "design" pressure is generally a padded number. Different companies have different criteria, but +50F above the maximum operating temperature is not uncommon.

In determining wall thickness for a pipe, that temperature generally doesn't have a big impact. But, for stress, particularly for rotating equipment, an extra 30-50F of padding can have a big effect.

The other thing to keep in mind for rotating equipment in particular - the allowables that we work with are based on deflection more so than stress. Long term exposure to excessive loadings causes unacceptable levels of shaft deflection, leading to early seal failures, leakage, and extra maintenance and down time. Short exposures, as you would see in an "emergency" condition are generally not going to damage the pump in the way we would expect in a pipe or pressure vessel where the exceeding the limits results in an actual over stress of the material.

So, while we very often need to provide additional flexibility in rotating equipment systems, we need to do so with a mind of why we are doing so and the consequences of making a system more flexible than it needs to be.

Hi John

Regarding modulus of elasticity for cryogenic lines, Since it is greater than ambient modulus of elasticity,loading calculation using ambient modulus of elasticity will be non conservative as well as non realistic as you already mention. But will it be violation of code B31.3( reaction 319.5)?

If say I use cold modulus of elasticity ( Eh1 by caesar) will caesar follow same same formulae for maximum reaction load for complex system (319.5.2) as it follow for simple system (319.5.1) ?

Regards

Habib

B31.3 suggests, under what situations, use of E at 21C can be less conservative.

Regards