Metal seated ball Vvlve leak 5

[zorans]

I have experienced following problems with 4" #1500 ball valves - metal seated, top entry, double-block-and-bleed.


4" #1500 Ball valve is with seats that are pushed by springs against the ball. In the middle of ball valve, there is 1/2" hole drilled to ball cavity in which we connected drain ball valve 1/2"#1500.

Here is the scenario...

1. With closed 4" ball valve was pressurized it from one side with 100 bar of natural gas.

2. With 1/2" drain ball valve connected to ball cavity we checked seat leakage by opening the valve and no leak was detected - which means metal seat is tight on that side

3. Using 3/4" bypass line around 4" ball valve we pressurized same ball valve from the other side on the same pressure - and still no leakage

4. 1/2" Drain valve was closed and 4" ball valve opened/closed - 3-4 times, letting gas go inside the valve and valve cavity

5. We tried to open 1/2" drain ball valve again to release the pressure from valve cavity, but after just small opening it was leaking and not stopping
for 5-6 mins

6. We closed back the 1/2" valve and tried to release the pressure after the 4" ball valve on 1" relief pipe down the line to atmosphere but the pressure remained 100 bar - like the ball valve is open

This all very strange to me.

I think it might have something with springs and metal sealing when the pressure enters the ball cavity -
maybe that pressure is causing springs and seats not to function well.

Hope for some help on this...

 

[zorans]

In original there were 12 springs.
We added 12 more but those 12 are actually spring in spring so total of 36 springs.

The result is that the valve that was holding 15 and 50 bars from different places are now holding 20 and 60 bars.

It is step forward but very small. Beside that valve was much more difficult to open/close.

Another thing I want to point out.

When valve in closed position is pressurized from the tap in ball cavity in the middle of the valve - seat are opening at 5-6 bar with original springs used. This is normal behavior if you look at seat image from my previous posts. Diameter where seat is touching ball is smaller than diameter where is the O-ring so pressure in ball cavity is easily opening seats once force due to pressure is higher than force in springs is.

I think it is the design problem as you can not trap pressure in ball cavity. What I want to say that is if you pressurize valve in half opened position, than close the ball and let fluid from each side go out from the valve, fluid should be trapped in ball cavity, but it leaks out until pressure drops to 5-6 bar. This is happening with valve that are good if pressure is applied from the side and you check leak on the other side.

 

[PeterIgg]

Just an observation on checking seat leakage via the cavity - you do need to take into account the volume of gas in the cavity. I would hazzard a guess that the volume of gas in the cavity would be around 2 - 3 litre. 2 l of gas at 100 bar is quite a lot. Is the pressure of the gas at the outlet still as great after 5 - 6 mins as it was initially?

 

[zorans]

We have gauge connected to cavity and the nitrogen connected to other side and in to the same cavity.

Valve is working like safety valve - once pressure rise to certain level, pressure opens against the spring.

This is bad behavior in my view, bat that scenario will never happen in exploration so it might be irrelevant.

Anyway in the past we tested valves with testing fluid trapped in cavity, but with this valves it not possible to trap testing fluid for more than 5-6 bars.

 

[tr1ntx]

as posted earlier:
"Manufacturer is from China" . . . well, there you have it.

I'm not trying to be a jerk about it, only to pass along what experience has shown me. Although the management of American companies, and European companies too I guess, have been in a mad rush, tripping over themselves to give the Chinese manufacturers all our hard-earned manufacturing technology in order to get items at a lesser cost, they don't always get it right. I've seen many cases where an important detail has slipped through the cracks, been "lost in translation", or just been ignored because it was too costly or unavailable. I've also seen more than a few instances where a Chinese "spin-off" company from one of the export parts manufacturers attempts to produce the complete product, but does so quite poorly. Crime doesn't always pay, I guess. (Not just China, India, Romania, etc. too, though I've seen it more from China.)

 

[PAN]

zorans,

Do you ask the valve manufacturer for this issue? What is their response?

 

[zorans]

Yes, I am in contact with them.

They have no explanation. I asked them to come and see what is going on but still they are hesitating about it. I also send them a video of out testing, but they answered that testing method is not good - which I agree it should be better, but we can not test real flow conditions in our lab. If they come and I take them to storage facility they will get real impression.

We had in the past bought many valves from them and always been able to fix if something is wrong with valves. What we did is always buy more items than needed than use them like reserve.

Once we also have been manufacturing ball valves, but with raw material being more expensive then their final product, we closed that production and now concentrating on testing valves before shipment and eventually fix malfunction valve.
But with this metal seated valves we have hard time to find the reason of leak and it is also for us impossible to repair or replace some parts as very accurate machining is required, which we do not have unfortunately.

 

[vpl]

Stepping in on this, though I realize it won't solve the problem:

The original poster mentioned that the vendor tested the valve with water, but that it's now leaking with air. My agency won't allow leak tests to be conducted with water when the final product has to be gas leak-tight (which is not a "zero" leak rate, but a "less than xxx sccm"). The different size molecules will allow a water test to pass, where it will fail the gas test.

Fixing it will probably come down to precision machining, unfortunately.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[zorans]

After long working hours, endless testing, strong headaches, ... it is now my opinion that the problem is not the design - this design is known as "single piston" and it must be down to material quality and its strength to resist deformations when high pressure applies.

I am not sure if anybody of established manufacturers has developed metal seated ball valves for this high pressures #1500 with "single piston" design approach. If so it would be good for me to know which is it.

 

[tr1ntx]

I'm pretty sure Vintrol can handle a 4" Class 1500 valve. E-mail is sales@vintrol.com

 

[Nilsoni]

First of all, changing or adding springs will not be any help. As you mention yourself the valve is a "single piston effect" seat, and the springs are there to seal at low pressure.
In my line of work we use a lot of MtM seated ball valves and gate valves. Valves designed to PSL3G and up to 10.000PSI (690Bar) and sizes up to 24" for subsea use and 25 year lifetime witout service.
I don't know your Cinese vendor, but we use only European vendors.
The trick with MtM ball valves are the hardfacining of seat and ball. I assume your valve has this, if not you can send the valve back to China.
At our vendors the last step before assembly and testing is the individual lapping of ball and seatring with diamond paste. This is done by hand by skilled craftsmen. If this isn't done right the valve will never seal at gas testing.
Another thing you mention is "pressurized cavity". If the bore pressure and cavity pressure are equal there will be no "piston effect" on the seatring, and the valve will not seal.
Reading this tread I think the problem are the valve quality and design. When you apply pressure to the closed valve the seatring will virually try to "swallow" the ball. And if the seatring are not properly designed, the contact area will move from the initial contact area at zero pressure.
If you want futher help send me the full documentation such as GA drawing with bill of material and FAT procedure.

 

[zorans]

@Nilsoni

Another thing you mention is "pressurized cavity". If the bore pressure and cavity pressure are equal there will be no "piston effect" on the seatring, and the valve will not seal.

------

Does it mean that none valve with single piston effect will seal or just these mine from China?

What I meant was do you know any manufacturer that has Metal seated valve with this kind - single piston effect type - that works?

Another thing we tried last Thursday and was on the facility and not in out testing lab.

We connected to 1/2" hole in ball cavity relief testing pipe 3/4" with opened gate valve to the atmosphere away from operator. Once valve in closed position pressurized from one side, leak was not detected on that 3/4" drain pipe. After that, over bypass valve, it was pressurized from the other side - the leak was not detected. This indicates that seats are good.

While opening that valve - rotating ball from close to open position, flow to atmosphere occurred on 3/4" drain pipe. Once ball in full open position - flow through 3/4" stops and when repeated from open to close position same happened.

This is prove to me that once I eliminate pressure in ball cavity, valve works fine.

This is what you say that if pressure is same in valve and in valve cavity - there is no piston effect, there are just springs pushing seats to close. I am not sure if any manufacturer can overcome this problem.

 

[tr1ntx]

"What I meant was do you know any manufacturer that has Metal seated valve with this kind - single piston effect type - that works?"

Yes.

 

[mqas]

Zorans,

A few comments which may not help you in this instance but should assist in the future.

1/ If you are purchasing a metal seated ball valve and it is intended for gas service then you should add additonal test requirements to your purchase specification so that the valve manufacturer has to perform a high pressure seat using gas. API 6D has an allowable leakage rate for liquid testing which cannot be correlated to leakage found during testing with gas.

2/ API6D has a series of static pressure tests and again additional functional tests should be specified in between the main body test and individual seat tests.
This helps to prove the repeatability of the valve test results.

I would have two concerns about the seat design: -

1/ The seat is very long and may be prone to tilting and locking, and this could be verified by visual examination of the seat pockets after test.

2/ Seat sealing face appears to be quite rigid and inflexible, therefore any movement in the ball during pressure test may not be taken up by a similar movement in the seat.

You could try lapping the seats to the ball using diamond paste and match the seats to specific sides of the ball. This could hel reduce the variability assuming seat tilting is not the problem.

Let me know how you get on.