Soft Seats being Shaved-off by the Ball

[Sid89]

Hi everyone,

We have some ball valves (1.25" and 6" sized)in which the upstream TFM seat is being clipped by the ball and damaging the seat which sends parts of the seat downstream.

Does anyone have any idea why this must be happening?

All valve parts have been designed and manufactured as per the dimensions so it shouldn't happen.

 

[The Obturator]

You state "All valve parts have been designed and manufactured as per the dimensions...."

Is it understood that you have made your own replacement parts and not used manufacturers own original parts?

The TFM seat (and other parts) may have same dimensions but is the actual material correct in all respects? hardness, composition, treatment etc.?

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Danlap]

Hi,

If I understand correctly, you want this forum to give you hint for your failure analysis report. Yet, no drawing, type of ball valve, photos, is this seat insert or just regular (floating) seat, process condition, operating temperature/pressure and more importantly timeline of the sequences??
Since you already put the blame on the ball... it is hard for me to imagine a round ball (without sharp edges) could slice seat without operator noticing it. They must have felt some resistance. One single hair sized brush wire could jam the ball in my experiences. I assume these sizes also lever operated..
Main keys of failure analysis is to remain objective: so IMO there are three suspect: manufacturing process; process condition and operational mistakes.

Not jumping to a conclusion, just examples based on experiences:
Manufacturing process:
- All parts fabricated from different companies e.g. ball, body and seat came from different companies. With poor dimension control. Once assembled, to overcome external leakage then excessive body to body torque was applied and might extruding the seat. Then seat was 'sliced' by process flow
- Someone might fabricates seat not according to OEM. Similar things as above occurred.
- loose parts might also causes same things.
- Only representation of batch was function and pressure tested. Ones that failed were not function tested.

Process condition:
- Operating temperature was above TFM 'creeping' temperature
- TFM is not compatible with the process condition??
- etc.

Operational mistakes:
- dirt got stuck on ball, thus 'help' slicing seat
- combination of all above, plus using ball valves a throttling instead of On/Off thus flow passing through cavity,
- etc. etc.

Regards,
MR

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

 

[Sid89]

The valves are actuated and service conditions are ambient. See below photos. If it had the dimensional problem, then why it is just happening on the upstream seat of a few valves? Dimensional inaccuracy could have occurred at the downstream seat as well.

 

[Compositepro]

The edges of the hole in the ball must be properly chamfered, or it will act as a knife edge. Also, excessive compression of the seal will extrude material to where the excess gets cut-off by the ball hole edge when closing the valve.

It appears that seal has been "rolled". This would be caused by very high friction between the ball and the seal. Friction between plastics and metals is very highly dependent on the surface finish of the metal, and there is a "sweet spot". Too highly polished will cause high friction.

 

[bcd]

This happens in a soft-seated ball valve when the upstream seat is not strong enough. When the valve starts to crack open, the upstream pressure (and flow) is bending the unsupported section of the seat into the ball port. As the valve continues to open, it chops-off the deformed portion of the seat. Need a stronger plastic or a way to retain the seat so it cannot bend into the ball flow port.

 

[gerhardl]

Hi Sid89!

Still difficult to diagnose without more info and detailed photos. Ball seal deformation/destruction will occur from a multitude of reasons, or combination of reasons.

It is already suggested deforming by rolling, which will occur from wrong dimensions, wrong mounting, wrong material quality or production, slack or misfitting parts, impurities, adhesion, material faults and scratches and other causes.

Often overseen is that cavity or drawing of materials will occur by cavitation over hairline cracks and scratches even by relatively low pressure differences.

Not complete closing and opening, or using the ballvalve as throttle valve is a common cause. Control and adjust endstops!

Fluid composition, impurities and 'cladding' on surfaces could contribute as well as pressure, temperature and impurities from the pipeline itself.

My guess? I would control that the affected valves are really accurately 100% closed or open first.

Good luck!

 

[LittleInch]

It's difficult to see what those red circles are trying to show - I can't zoom in enough.

Are these valves being operated 15% open so those marks line up with the ball to seat location? They appear to be nicks or cuts in the ball itself?

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