Ball Valve High Torque: Water Service

[Phil121324]

Hello,

Im looking for some support, research paper, standard or maybe just good old experience to assist in determining the cause of some high torque on some ball valves in water service....

There are 20+ ball valves where i work (water injection facility) that are problematic to open under rated differential pressure. To get around these issues valves have been positioned "just closed", approx 5% open so then when they need to open the travel is minimal OR we have to equalize pressure across both sides of the valve.

The valves are 10"class 1500, Stallite clad ball and seal sealing area, trunnion mounted, SPE, according to OEM documentation the FOS on the BTO is approx 298% (3x) the required. However, as stated we still have operational issues constantly with these valves. We have valves from different manufacturers, with similar size actuators and they both have the same issue.

The valve is relatively new(3 YEARS), my immediate thought is the excess torque is being caused by the seat to ball seal face and not the bearings, just my thoughts as the likely cause.

The valves are regularly opened against rated DP, perhaps overtime the sealing faces have shined up/lapped in/matched nicely and this may be causing the high torque.

Does anyone have experience of this, im interested to know how you might think the water service could be affecting the opening of the valve? One thing to consider with the water is what happens when your Beer glass is on a table and condensation has formed on the outside, you go to lift your glass up and it's stuck to the table or hard to move, could this be happing inside the valve????

any thoughts...

 

[LittleInch]

Phil,

First you will need to supply some technical information to us or any other valve company.

So what is the deign maximum opening torque against full DP?
What is the opening system - gear or powered actuator?
Can you post a sectional view through the valve?
What is the measured opening torque?
What is exactly "problematic"? Does it just take a bit more effort? or can't you open them? does the actuator fail?
Have you tried to inject lubricant into the stem and trunnion?
Have you removed any of the valves and taken them apart to see where you have excessive wear?
What does the vendor say / what do the manuals say?
What it in the produced water?
How often in the last 3 years would you estimate that you've opened these quite large high pressure valves against full DP?

Of course ball valves are not really intended to work this way. I accept that's what tends to happen, but once you go to 10" class 1500, that's a huge force on the ball and seat and increase in opening torque is not surprising.

And no - the glass on the table issue is not the same as what you have.

Was the original design to open these under full DP or is this something which the operators have started doing?
It's surprising to me that anyone would design such a system to do that on a regular basis.

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

 

[Phil121324]

Thanks LittleInch, appreciate the response:

Details below:
So what is the deign maximum opening torque against full DP?
Calculated BTO is 8500Nm (at stem)
MAST 29000Nm
What is the opening system - gear or powered actuator?
Pneumatic spring return, currently set to provide 29000Nm

Can you post a sectional view through the valve? See below, very similar but the valve we have is metal seated
Trunnion plates, 3 piece, ball valve (i carnt post image for some reason)
What is the measured opening torque?
Its not measured, however, regulator set pressure for the actuator is set at the maximum allowed to provide the 29000Nm
What is exactly "problematic"? Does it just take a bit more effort? or can't you open them? does the actuator fail?
Valve will not break open on some occasions, other times it does but mostly not. DP is always minimum 180bar.
The valve and actuator assembly operates fine when subject to balanced or Zero pressure
Have you tried to inject lubricant into the stem and trunnion?
No injection points, the volume of water traveling through the valves will remove any lubrication very quickly, flushing won’t be effective for this reason also
Have you removed any of the valves and taken them apart to see where you have excessive wear?
Not yet, awaiting valve to be removed for investigation: given the price of oil at the moment it might not happen for a while.
What does the vendor say / what do the manuals say?
No help from OEM, MAST is the MAST and they did not have any issues during FAT
What it in the produced water?
Sodium Hypochlorite
How often in the last 3 years would you estimate that you've opened these quite large high pressure valves against full DP?
Approx. 50
Of course ball valves are not really intended to work this way (Why?). I accept that's what tends to happen, but once you go to 10" class 1500, that's a huge force on the ball and seat and increase in opening torque is not surprising.(Why?- valve should be designed for the size and class)
And no - the glass on the table issue is not the same as what you have.(Why?)
Was the original design to open these under full DP or is this something which the operators have started doing?
The valves are rated to be operated under full DP

 

[LittleInch]

To attach a file click the "click here to upload" link at the bottom of the post and follow instructions. To add an image into the post click the camera symbol and browse to the file and then click upload.

Thanks for the extra information - very useful.

As said, ball valves CAN open under full DP, but the normal design process is that they don't do this as a regular thing, especially once you get to the bigger higher pressure sizes. One reason is that as the valve starts to open there is a split second where there is a very small orifice as the ball moves and the fluid squirts through at several hundred m/sec. This can easily damage both the seat and ball. Even if the seats are metal, they often include elastomeric elements to add sealing capability to the valve. They get ripped off fairly quickly if you open under high DP many times.

The force on the trunnion is huge - 200 bar DP on the ball is a force of approx 100 tonnes force. That is being resisted by a relatively small area of bearing on the trunnion bearing and the lower stem bearing. The force from the seal is much less as the area of the seal is quite small but can add to the opening torque.

This is why when you repeatedly turn the ball with this level of force the trunnion starts to wear quite rapidly. And also why ball and gate vales for that matter are essentially isolation valves, not normally used to open under very high DP. For that you normally need to use a globe valve or control valve which are designed to open under high DP and gradually open to allow fluid flow to start.

So yes, the valve is designed to open and close under full DP, but unless you specifically told the vendor that this was a normal mode of operation, then the valve is likely to start exhibiting the behaviour you are finding. Especially nowadays where everything has been trimmed to the limit to reduce CAPEX.

I am a little surprised that anyone would design a system to normally operate this way which was my question as to whether there are ways to equalise the pressure before opening the valve or if this has been bypassed?

As for the beer glass thing - the water creates a seal either around the edge of the glass or within the base of the glass. Then as you try to lift the glass, the very small air bubble under the glass can't let air in and the reduced pressure creates a force on the base of the glass from atmospheric pressure. This is very different to a valve under high DP.



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

 

[Phil121324]

Thanks again,

For the small orifice observation, i don't agree but i understand the point your making. I worked for a valve OEM, conducted many PR2 and endurance tests on metal seated (TCC) valves, and didn't see this issue occur....not saying it can't happen.

For the bearing issue, yes, agreed, high force, worn bearing, = increased torque.

Lastly, the beer glass thing, i understand the concepts are different but i think its still worth looking into, I could be barking up the wrong tree! but....I still think sure something is happing with the friction between the two surfaces of the ball and seat with the water layer in-between. I have seen this also during endurance at the OEM i worked, 5000cycles testing: 5 1/8" API 6A, 10KSI Ball valve, HSR, over time the torques continued to increase, however no notable bearing / busing defects on disassembly.

I also posted a question here

https://www.eng-tips.com/viewthread.cfm?qid=492649

regarding the potential change of COF....who knows!!

Thanks again for your detailed response,

 

[LittleInch]

OK, you've probably got more info than me - my experience is possibly more relevant for gas where you might get higher velocities for longer as the valve starts to open. The soft seats within a metal seat if you have them are the bits that get damaged, The meatal seats and the ball will probably be ok, but any inserts or lip seals just get destroyed after a few high DP openings. IMHO.

You may well get some increase in friction and a bit of wear between seat and ball over time, but after many cycles I think the majority increase in torque will come from the bearing surfaces. Fluid surface affects are minor compared to this.

But I still find it odd that this was the original design concept - normally things like this would get picked up in HAZOP that it's not a good idea to use a ball valve of that size and pressure as a working on/off valve.



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

 

[bcd]

My initial thought is different than yours. Not sure why you chose to focus on the ball and seat interface first. My first focus would be on the trunnions and ball stem connection. My reason is that the trunnion bearings are what support the pressure forces on the ball and generate a majority of the torque. My reason to focus on the ball to stem connection is if the trunnion bearings wear, a tight spline or key connection between the ball and stem can cause binding of the stem.

The seats should be spring-loaded and allow the seat to move away from the ball and maintain relatively constant contact force against the ball. Polishing the surfaces will not triple the coefficient of friction.

But, with no picture of what the valve looks like, we can only guess at the possible problem(s).

 

[Nick_Gray_88]

Erm, what concentration is your Sodium Hypochlorite? Usually when there is any of this you’d used a Titanium valve.

The actuator output is also set to the MAST rather than a multiple of your BTO I.e. BTO x 2 would be 17000Nm. So looks like you’ve damage the stem or drivetrain or related components in the valve due to tolerance in actuators you’re likely getting an output more than the MAST.