Dear particular,as far as we konw,when valve is closed quickly,there are water hammer generated either upstream or downstream of this valve.But refer to turbine trip,the main steam valve at the inlet of HP turbine will be closed quickly,we know there will be steam hammer act on main steam pipe which at inlet side of HP.But at outside of HP turbine,is there steam hammer as same as downstream of closed valve?How can we consider the influence of the turbine?And did you calculate steam hammer of Cold reheat steam of plant?
Thanks for your reply in advance!

Maybe somebody have this experience,would you please share it with us?

twing,

The difference between water hammer and steam hammer will hinge on the relative incompressibility of liquid versus compressibility (and expansion) of vapor (steam). Yes, the possibility of steam hammer at the trip valve at turbine inlet should be considered and restraint provided.
The downstream flow after the turbine will not be like that of liquid that might have column separation with vapor pockets. The fluid is already a vapor. The turbine extracts energy out of the steam flow. Pressure and density are reduced at the turbine outlet. The vapor would expand to equalize a reduced pressure pocket in the downstream piping. If there is a trip valve for the reheat section of turbine then a similar calculation of steam hammer could be done using the reduced pressure of reheat steam for inlet to reheat trip valve. I don't have experience with reheat turbines to say if there is an actual steam hammer observed at the reheat outlet, or not.

Thanks RechardYee,I agree with you about different between steam hammer and water hammer,and I think that the turbine's rotato will influence the pressure wave in cold reheat pipe,so maybe my question is how can we analysis steam hammer in cold reheat pipe?
Best regards!

Cold reheat pipe will face sudden decrease in flow from steam turbine outlet. As steam density and velocity are lower than the same in main steam piping, steam hammer will not be as pronounced.

It is neither very cheap to carry out this analysis, nor it is required - below 500MWe units or nukes, we have never carried out this analysis.


If turbine trip closing time is not very fast - say not below 100 millisecond, one may not have to bother much about steam hammer.

One should have a validated fluid transient software, model volumes of boiler suprheater, reheater, steam turbine stages, SRVs, trip valve, steam turbine bypass piping & valve - all with some simplifying assumptions based on experience & then have to be prepared to mitigate the effect with strategic placement of optimized combinations of mechanical snubber & rigid struts for both turbine trip & seismic event & co-ordinate with structural group for restraint load transfer.

regards,
sam

Thanks for your reply,Sam.
As far as we know,in EBASCO's rules,if the MSV'S closing time is lower than 0.2 second,we must consider steam hammer to main steam pipe,but refer to cold reheat pipe, there is no limit in our rules.
Our design plant is 600MW ,and the MSV's closing time is 0.12 second,so we must consider the influence of steam hammer.
Regards!

You are right; you should consider steam hammer force.

In cold reheat piping, you will have steam hammer due to fast closure of MSV, after that say, HPT modelled as 1 m^3 volume, NRVs, CR piping, RH (relatively larger voume), HR piping & HR control valve. Here, the MSV closure of 0.12 s is the reason of highest steam hammer pressure rise/fall in MS/CR piping & consequent force. If you have access to a fast transient capable simulator or you have experienced a turbine trip from control room or data logger prints of a similar size, you can better understand the sequence.

regards,

sam

Sam,Thanks for your reply,it's so helpful to me.
My trouble is that I have no any data about turbine trip and we all use pipenet transient(peoducted by sunrise of U.K) to calculate steam hammer,but there is no model of turbine in it.so our result of CRP steam hammer will ignore the influence of turbine's rotato,but I think it's an important thing to CRP's steam hammer.Would you please tell me which transient soft you use?
Best regards!

Last four years I am away from power plant design.
I have used our organization's own software. Every good E&C firm in power sector has at least one such software calibrated with industry standard benchmarks.

You can use BOS FLUIDS in public domain software, Bechtel's GAFT for single phase steam hammer & well known nuclear safety code RELAP5 for multiphase fluid transients.

But, with PIPENET-Transients, you can have have this analysis done with some small loss of accuracy which you can cover up by some factor of safety.

regards,

sam

Thanks for your patient explain,Sam.
Maybe I should go to some power plants to collect more data about turbine trip.Heretobefore,I have no any data about steam hammer in CRP,and I have not hear any accident about CRP steam hammer,maybe our design is too safety coefficient.But who can promise his desin is safe absolutely?At least I can not now because I have not learn about the stage of steam hammer in CRP.
Thanks for your reply again.
Best regards!

According to ASMEB31.1 Appenix V-10.2,it's as follows"Piping response to these momentary unbalanced loads can be significant in high pressure steam systems,such as main steam,hot and cold reheat steam,bypass and ..........",but it's nonmandatory,so we have two choice:one is consider more and pay more,another is ignoring the steam hammer in CRP to save some cost of snubber or material.Which one choice would you select?
Thanks for your kind attention!

You have to realize your responsibility of maintaining integrity against collapse. due to primary load, of piping after full load trip; for an unitsize of 600 MW, it may be costly to ignore steam hammer just to save cost of rigid struts, mechanical snubber, associated civil structural strengthening & analysis.

You must have some reference plant design / mentors to use as seed for calculation.

Making piping flexible to meet steam turbine allowable loads & stability calculations are for better operability. To have good slopes & steam drain facility in piping & code comliance for steam hammer is for avoiding deformation & accident post full load trip. None can be ignored.

regards,
sam

sam Member Member # 884 March 07, 2006, 02:50 AM: Message edited by: sam

RE: You can use BOS FLUIDS in public domain software.

TECHNICAL NOTE:
BOS FLUIDS by Paulin Research Group http://www.paulin.com/

My understand is not public domain software.

I am very sorry for wrongly writing 'Paulin Research Group's BOS FLUIDS as public domain software.

What I wanted to write that it is a software whose user license can be bought unlike the proprietary softwares of A/E firms.

It's my mistake, I accept.

regards,
sam

Dear sam,you are right,none should be ignored,especially we have no data about steam hammer in CRP.But you know,stress engineer consider more about the safty of the piping system,but the owner cosider more about the cost.If there is no snubber on CRP in all his other plants,the owner will ask why we use it here,I shall only answer:"more cost mean more safty." so maybe it's only my business,but I want to know who have used snubber to prevent steam hammer of CRP in our form.If all not,at least we can know that is not more important in our analysis.
Sam,Thanks for your kind again,you help me a lot.

Twing, If you have some idea of the steam hammer load from minimum to maximum you could use your availble software to undertake a sensitivity analysis. This could take into account the turbine rotation etc.

If this shows no problem over a large range of conditions you can justifiably go no further. If you find there are problems you may need to engage a specialist company to show you how to analyse it. Then in the future you can invest in the correct software and perhaps do this analysis yourself.