Caesar II 2011 - Pump Nozzle Loads & Moments

[Erhard]

It seems to be a problem for a lot of piping stress engineers using Caesar II for calculating nozzle loads on pumps/vessels/exchangers/etc.

Depending on the equipment, our business rule will depict whether we will model in the equipment or not. In cases such as vessels/exchangers we will model in the equipment due to the expansion coeff of the equipment material itself that will play a part in the expansion/growth of the equipment with the expansion of the piping.

In cases where pumps are involved, we would usually just anchor the line at that point, however the general feel is that the point on the flange is not rigidly fixed, and thus the use of a stifness parameter should be used?

My query thus do there exist a table with typical stiffness coeff/rates that could be used in Caesar to ease the high nozzle loads/moments calculated when only anchoring the line at a specific pump suction/discharge nozzle?

Any comments welcome.

 

[BigInch]

Anchoring a line to a 100% rigid nozzle will almost always produce high moments, usually over allowables. You can reduce rigid end moments by entering a rotational spring constant (stiffness parameter?), but at the expense of permitting rotation, which may be greater than what is allowed to meet casing distortion and misalignment limits. I've seen allowable nozzle loads for pumps, but not allowable rotational deflections, which as you imply, only addresses 1/2 the problem.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[SNORGY]

I have gotten into the habit, when feasible, of trying to model the volute of the pump as a short length of pipe with nozzles oriented in such a way as to closely match the pump geometry. Then I can use rigid elements to connect that geometry to the actual point of fixation in the pump assembly.

You could use the maximum casing distortion values in API-610 and try to derive a stiffness or spring rate, based on correlating those to a API maximum allowable loads.

The conservative design approach would usually be to assume that the nozzles are anchors and lay the piping out so that the load analysis passes.

You might want to re-post or move this thread to the COADE CAESAR II forum. Those guys avre very good.

Regards,

SNORGY.

 

[SNORGY]

And...again...stupid keyboard.

Regards,

SNORGY.