Piping Loads on steam turbine

[garfio]

I need to check the loads imposed by piping to a steam turbine. The turbine manufacturer has provided the allowable loads per NEMA SM-23. A quick look to these allowable loads shows that one of the constraints is that the resultant force at the turbine inlet shall not exceed 500 lbs.

Being a 450 psi steam system and a 3" inlet nozzle, only the pressure thrust generates a load of about 3,300 lbs on the turbine inlet nozzle, far in excess of the allowable load.

The steam pipe comes on a pipe rack turns down (after a horizontal loop) and turns horizontally towards the turbine. There is a stanchion below the last elbow.

I don't see that a expansion joint will help either because even the pressure balance type balances the "spring force" but not the pressure thrust.

The turbine and pipe expansion will generate an opposite force on the turbine nozzle and stanchion, but relying in this fragile balance seems unsafe.

However I have seen inlet lines in small turbines connected as I am describing above (not necessarily saying that is right).

My questions are:

1) Is it correct to include the pressure thrust when verifying compliance with NEMA (or API when pumps or compressors) allowable loads? It is a real force on the turbine flange, but it will make impossible to satisfy the turbine allowable loads.

2) Is this piping arrangement the correct solution or there are better piping arrangements that can allow taking care of the pressure thrust?

Any other comment or information will also be greatly appreciated.


Thank you

 

[ColonelSanders83]

1) The caseing is designed to handle the pressure thrust of the piping internal pressure (much like any other flange joint). The allowable nozzle load values refer to external loads imparted onto the turbine by the piping i.e. live load, dead load, thermal grownths, seismic, wind ect. Pressure thrust is only taked into acount when using an urestrained bellows joint.

(P.S. your statement regarding pressure ballanced bellows is reversed. Pressure balaced bellows will have no pressure thrust, you only need to be able to handle the forces and momnet imparted by the bellow spring rates see here

http://www.usbellows.com/products/elbow_joint.htm

.)

2) Pressure thrust as you have described it, is not applicable. Evaluate the combined forces and moments imparted to the turbine from the piping due to all loads and operating conditions and compare the reactions to the allowable.

Please note that the 500 lbs is not a hard value and can easily be mush less depending on how the other nozzles from the turbine are being loaded. An individual nozzle limit is very rarley, in my experience, the governing load.

From you post it seams like you may be justified in hireing an expert to determine the adequecy of you turbine.

Just my two cents worth.

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

 

[rmw]

The pressure thrust you seemed concerned about will be reacted by the turbine foundation.

ColSanders has it right regarding the pressure thrust (or lack thereof) for a pressure balanced bellows vs. an unrestrained bellows.

rmw

 

[racookpe1978]

Work up your proposed design, and the resulting loads. You can guess and re-guess and re-approximate all day, but you need to put a design down on paper/drawings so a second person can evaluate it.

Get it evaluated by a consultant (Reviewed by a second experienced engineer, drawings together with your calc sheets AND assumptions for your external loads, at a minimum.)

Review results with the turbine supplier. (They (the supplier) really do want your business, and don't want your project to fail - and cost them reputation and money.)