Maximum Differential Pressure for Gas Pipeline Ball Valve

Is the company unreachable because of no longer existing, or because of inconvenient location? If the latter, maybe someone can help.

The company does not exist any more.

So, how is it known that this code exists? For if the company no longer exists, it cannot update any policies.

...and if it doesn't exist any more then its code is unenforceable, notwithstanding the fact that companies don't have the ability to enforce.

Further, companies don't issue codes of practice for other companies to follow. Institutions do.

Further, the company in whose domain the valves are installed is in a position to write its own standards.

Further, the author and applicability of the code of practice should be stated therein; there is therefore no need to ask an international Engineering forum as no other subscriber here can actually read it. And if it isn't, then it's just a chink of useless text.

Is it the differential pressure or the sonic velocity that's thought to be the problem? Sonic velocity can occur at low differential pressure, depending (as you say) on pressure ratio.

Any reason why you jump from 50 psi to 50 bar?

You could speak to other manufacturers, the constraints are likely to be similar.

The problem seems to be the wear of the ball and the seat, so I guess it's the high velocity.

Regarding the jump from 50 psi to 50 bar: The recommendation about not exceeding dp more than 50 psi, was found by googling. The 50 bar is the actual working pressure. Hope it is clear now, sorry for the confusion.

I have asked one manufacturer which repied that his valve can reliably open and close under the full differential pressure that the valve is designed for.

But in practice, there is erosion of the seat and ball when there is high velicity, and we should avoid unnecessary wear of the seat and the ball. So, does this unnecessary wear start at dp 1 bar, 50 psi, or 15 bar?

Google says:

7.2 Pressure and temperature ratings The nominal pressur

API 6D: Specification for Pipeline Valves

Piping codes, valve standards and ball valve selection

Thanks Lyn, I have looked at them, but they do not answer my question.

SolarEagle, thanks. The 100 and 200 ft/s is for the average speed of normal flowing gas, right?

Yes for the pipe...The material and design of the valve will determine the parameters of flow velocities....without that information you have to go with the worst case scenario...

"Gas moving through a pipeline at 100 ft/sec is moving at approximately 68 mph and at 200 ft/sec approximately 136mph. A good rule of thumb is that when inlet pressure is more than twice the outlet pressure (both absolute), critical conditions will exist and high velocity will be present. Elbows, tees, flow restricting valves, reducers, and increasers will create turbulence affecting velocity and capacity.

Another consideration is the temperature of the gas and the effect pressure reduction has on the gas. For every 15 PSI pressure drop equals 1 degree Fahrenheit temperature drop. Low temperatures can cause ice to form around the outlet piping, causing cracks in concrete pads, or upheavals in the outlet piping. This may also create water and hydrocarbon condensate in the gas stream."

This multitude of considerations is what makes the questions in the thread so good. Possible chilling and condensation of liquid fractions could induce liquid hammer in the piping, for instance. (I don't know if that is much of an issue in methane or natural gas piping, though it can be in refrigeration piping.)

Don't know if this will help...I think a lot depends on the valve design....

"The rule of thumb concerning velocities in ball valves is to limit the gas velocity to 100 ft/sec in above grade piping and 200 ft/sec in below grade piping. Staying at or below these thresholds along with properly supporting the adjacent pipe will minimize or even eliminate any vibration that leads to mechanical wear and fatigue at the pipe joints."

http://asgmt.com/wp-content/uploads/2016/02/108.pdf

The criterion of DP < 1 bar would pretty much prohibit opening many valves altogether. The language might need some clarification or adjustment.

If you are using a ball valve in a throttled position, this may be the problem. Ball valves should be open or closed, not throttling. I was unaware of any differential pressure requirements but a max pressure should be observed. I would think any differential pressure up to max working pressure would be fine. I concur with a previous post about looking at several other manufacturers valve specs.

You may want to check the actuator sizing to see what it is rated to open against. Is the actuator electric? To actually calculate it might require more information than you have but in pipeline service they may not be rated to be opened at high DP.

During my career I learned, was taught, engineered, used and problem solved more utilizations of ball valves than I want to remember. From the start, I was instructed by a very experienced master pipefitter that only in an extreme situation is a ball valve to be used for throttling. The primary reasons is that there is only a 90deg movement of the handle to go from no-flow to a full-flow. This is a big change in flow from only a small physical movement of the control handle. Also, the ball within the valve, will probably abrade due to any particles in the liquid, slurries and even drinking water will do this over a long time period that it is in use. Gate or globe valves are better for throttling use.

About fifteen years ago a saleswoman came in and insisted that her brand of ball valves could be used for throttling. She didn't know why but insisted that it was true. She sounded like the "pep-talk" from a sales meeting.

Of note, ball valves are usually available special order for the handles to be perpendicular to the bore when in the fully open position. Great for limited access situations. This is done on many portable shipping containers such as what is commonly referred to as a "tote container". The valve is located on the bottom adjacent to the side wall. Using a regular valve handle puts the handle beyond the side wall where it could be hit causing the valve to accidentally be opened or broken.

Also, for higher flows consider the use of a "full port" ball valve to get greater flows from the same size valve body.

Old Salt

I know this is an old thread, but...

Not everybody's keen on gate valves for throttling.

For gases and liquids with negligible solids, butterfly valves are fine. Another good choice is eccentic plug - Masoneilan Camflex, de Zurik or similar (a few manufacturers do that type)

Codemaster-

Thanks for the correction! I had no intention of including "gate valves". I, as most others know, gate valves are one of the worst types of valves to use for throttling. They are prone, especially when solids or other types of abrasives are in the materials are being throttled. The gates and the seats wear rapidly and then the valves begin to leak through.

They also give very non-linear flow rate changes when compared to changes in the gate position. In almost every application, gate valves should be used in only the fully open or fully closed positions.

Old Salt

Well put