Steam hammer and Cold Reheat Piping?

[c1rowy]

It is well known that for Main Steam (Live Steam) and Hot Reheat piping steam hammer caused by turbine valves emergency closure need to be considered and calculated.

My question concerns Cold Reheat Piping.

Closing HP turbine valves cause immediate stoping of Main Steam flow. But also the flow in Cold Reheat Piping (which is downstream the HP turbine) stops (the same period of time). I did some simulation which shows that unbalanced forces induced by pressure differences between bends in Cold Reheat piping are significant and in my opinion should be taken into account.

However, reviewing stress calculations (done by other engineers) I can not see such a case to be considered for Cold Reheat piping.

I know that there is HP turbine betweenn Main Steam and Cold Reheat Piping, but still I can not find a reason why it is ignored.

So the question is: what do I miss?


Thanks in advance.

 

[davefitz]

There may be 2 comments to address CRH pipe and "steam hammer".

First, the momentum pulse from the closure of the STG intercept valve is likely dampened by the multiple small tubes and alternate flowpaths presented by the reheater heat exchanger assembly- this can be field-tested using fast trace pressure transmitters.

Second, there is a worse case , which is "water hammer" that has occurred many times on some incorrectly drained cold reheaters. In units without a steam to reheater bypass system, water can accumulate in the cold reheater if the cold reheater is either drained to a common flash tank in common with the superheater drains or is not correctly and directly drained to the condenser, because the reheater will operate at vacuum prior to STG synchronization and can pull liquid water up a 7 m gravity head. At the instant of STG synchronization, a steam pulse will accelerate the water that accumulates in the cold reheater transfer pipe and will straighten out the elbows, and frighten the operators.

"Nobody expects the Spanish Inquisition!"

 

[c1rowy]

Thank you for reply.

The first one is something I'm afraid of.

I agree that momentum pulse will be dampened when it reaches the reheater.

But the "low pressure wave" in cold reheat piping starts at turbine side.
So it goes from turbine to reheater and produce unbalanced forces at each straight pipe.

Am I right?
If so, can Joukovski formula be used to calculate forces at each straight pipe?