GATE VALVE BEHAVIOUR UNDER PRESSURE

[GAL02]

Dear all, Good afternoon !
Regarding the subject matter Gate valve following is the situation for which I need your expert & experienced feedback.
We are working over Steam Super Heater (High Pressure High Temperature service) who's outlet isolation Gate valve not getting operate i.e.
Open or Close) by manual Gearbox (Actuator Damaged due to malfunction) and now Gear box Drive Bush catches the stem (Due to thread damage)
situation is as follows:
1) Super heater develop leakage & need to attend urgently.
2) To isolate super heater need above said valve (12" X 10" X 12" X 2500 # BW)which is not getting operate.
3) If we want to remove Gearbox it need valve to be close (which is not getting operate)the valve to install new gearbox.
4) If we try to cut the gearbox to remove inside Drive Bush then what will be the valve stem behavior when line under pressure
of 130 Kg/ Cm2 and Temp. 135 ° C

Pl. Advice what will be Valve stem behavior if it will be un supported when line is under pressure (130 Kg/ Cm2 and Temp. 135 ° C)


With regards

 

[MFJewell]

Why not isolate further downstream in the system? Relying on single isolation for high energy systems is not a good idea by the way, you set yourself up for problems doing so.

 

[Danlap]

Better to kill the line prior do such hazardous job. It is not worth the risk

Your risk:
(correct me if I am wrong miss-interpreting your situation)
a. Quote"super heater develop leakage" meaning there is passing under the wedge than could easily lift the wedge uncontrolled. Thus spindle blow out
b. Quote "due to thread damage" this is the one that you visually can see. maybe the wedge/spindle is also crooked. Anyhow now you want to remove the only gearbox which the spindle hold upon. See point a
c.

http://www.eng-tips.com/viewthread.cfm?qid=236759

Many operator says line cannot be killed due to enormous cost they will bare. that is partially true. But live is not worth a gamble (if someone dare to do the job).
what I can imagine are (since this is a butt welded valve)
- prepare the new spindle or its raw material, body bonnet packing, wedge (or its lapping machine), new packing
- make a step by step plan, bypass all bureaucratic protocol to save time, but someone from HSE to supervise the action with minimum risk
- Kill the line and depressurized
- open bonnet,
- do machining, lapping, etc.
- it may not fix your problem totally, but worth a try

OR
- make some "yoke" anchored to the valve body to retain the spindle from blow out
- Refine the thread, install new gearbox.
PS: I am very pessimist about this solution due to your valve is passing and the leakage rate is unacceptable. So something is wrong inside (and not just the spindle)

anyhow, good luck,

Regards,

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[LittleInch]

Without seeing the details of the valve shaft and gearbox arrangement it is very difficult to see or judge what is likely to happen.

The valve might open, stay in position or close - very difficult to tell at the moment.

Also without knowing what you're tying to cut off or whether there are any worm gears in there or all staight cut gears

But this looks like a big mess and you don't say why the gearbox has failed, how old it is, what condition it is in etc etc.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GAL02]

Dear all, good morning!
Thanks for your valuable feedback.
I guess that there is something is not clear in my query, that I am going to made it clear.
Plant is 57 years old.
Super Heater Outlet Valve, (Connecting to main header)
1) Valve: Gate Valve
2) Size: 12" x 10" X 12"
3) Connection: BW
4) Class: 2500 #
5) Pressure Seal bonnet
6) Service: Saturated Steam (540° C)
7) Temp.: 540° C (Wrongly mentioned 135° C earlier)
8) Pressure: 130 Kg/ Cm2
9) Valve Position: Open (70 %)
10)Connect direct to main header, 130 Kg/Cm2 (4 boilers are in line)
11)Can't Isolate the line (Valve)from main header.
12)If main header isolate then whole plant will down & huge loss to production.
13) No spares available, valve production stopped by 'OEM' - 40 Years old valve.
14) NO space to anchor valve stem to hold in position if want to open the gearbox by cutting in two pieces.
Question: If we release the stem (Free the stem)from drive bush what will be the Stem Behavior under pressure of 130 Kg/Cm2?
Does gate fall down by gravity?
Does gate & stem move upward with enormous pressure?
Pl. Find herewith some of the photos & Gear box.

 

[MFJewell]

12)If main header isolate then whole plant will down & huge loss to production.

Sometimes you have to bite the bullet and doing things the right way. Is production more important than safety? With proper outage planning and staging of parts, you can minimize downtime. Good luck, hopefully nobody gets killed.

 

[GAL02]

You are very right, but just we want to check any possible option which can be execute to save production "safely".
For us my team "SAFETY is FIRST".

Thanks a lot to share your views.

With regards

 

[LittleInch]

We still have no information, drawing, photo or sketch to know how the stem is fixed to the actuator/gear, where the damage is, what the stem looks like etc etc.

It might be possible to remove the actuator, it might not depending on where damage is and what the stem drive components are.

All we have is your description and a very basic GA type drawing. Not enough to make a judgement.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.