water induction preventing main stop valve to work.

[JokaSteel]

Hello,
I'm facing a problem where has been said that a huge water induction in a steam turbine prevent the main stop valve from close.
I wonder to known if this sounds good for anyone or about papers that treat this subject.
Thanks.
JokaSteel.

 

[mk3223]

Can you share a simple system sketch to show what's the problem of the stop valve?

 

[JokaSteel]

Hi mk3223,
Thanks for your post.
Unfortunatelly, I don't have any sketch. I do known that huge water induction took place from a high level boiler situation.
The turbine's main stop valve has been found 80% closed (near of). As the huge water mass was passing through at the same time stop valve was closing, I need to known if such mass can prevent the valve from 100% close. I search for this in the internet and found nothing. Also, no words or warning on valve's books and manuals about such possibility.
Please, let me known if you have any ideia on this subject.
Regards.

 

[stgrme]

There are two main consequences from water inductions: damage from the impact of a "slug" of water and thermal quenching causing high thermal stresses. Impact damage to internal parts of the main stop valve could result in broken parts preventing the valve from fully closing and/or damage to the valve seat.

Thermal quenching can result in distortion of the valve body and/or internal parts, which in turn could prevent the valve from fully closing.

Failure of a main stop to fully close (even a small leakage path) after a turbine trip could result in a catastrophic overspeed of the turbine rotor.

I suggest that you disassemble and inspect the main stop valve immediately.

Also note that the turbine could suffer similar consequences. In addition to those described for the main stop valve, distortion of the turbine's stationary parts could cause "rubs" and "bowing" (a permanent bend) of the rotor.

Best of luck!

 

[sjrfc2]

I'd look at the effect of the momentum of the water. If it's a gate valve, the mass of the water against the gate, (as opposed to the mass of steam) will create a lot more drag and make it hard for the valve operator to work. In that case it would stall.

 

[stgrme]

Further to my earlier reply, you should obtain a copy of ASME Standard TDP-1-2013, Prevention of Water Damage to Steam Turbines Used for Electric Power Generation: Fossil-Fueled Plants. This document is the most comprehensive guide for design, operation, inspection and testing to avoid turbine water induction. For your incident in particular, see Design Sections 3.1 and 3.2, Steam Generators and Steam Attemperators, respectively.

Best of luck!