INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Typical (average) MTBF for Actuated Ball Valve

Typical (average) MTBF for Actuated Ball Valve

(OP)
Hi,

This post is related to the previous thread "ball valve & actuator assy in vertical orientation".

I'd like to get some inputs on a typical MTBF for a ball valve in 110 bar, 80 degC operating conditions, vertical mounted.

Thanks!

RE: Typical (average) MTBF for Actuated Ball Valve


MTBF (= mean time between failure?)

Any mechanical device, made up of several components, will obviously depend on the quality of each component, nothing better than the weakest link and weakest part of any component.

Any comparison between similar (but not in all parts equal) products, could give an indication, but nothing more.

The best practical advice would be to check and test your product at the time for normal production equipment check for other production equipment. If really critical for the plant, and high cost of unplanned stop, it would be reasonable to have one complete unit (actuator inclusive) in stock as spare, and change to the new at regular inspection stops. You can then check and repair the one taken out separately.

For theoretical information it would probably interesting to have a look at the European view:

https://en.wikipedia.org/wiki/Safety_integrity_lev... or this forum thread408-180990: SIL certification



RE: Typical (average) MTBF for Actuated Ball Valve

(OP)
Thanks gerhardl.

Yes, MTBF I meant is Mean Time Before Failure.

We've just got 3 occurrences with failed ball valve (stem tilted due to side load, exerted by heavy actuator), and all occurrences are days apart. Thanks for your input on the risk assessment for the failure, and the need to look at our spare parts strategy.

RE: Typical (average) MTBF for Actuated Ball Valve


Hello Orga78,

I see now the connection with your thread408-428919: Ball valve and actuator assembly in vertical orientation (stem in horizontal direction).

With your post above describing incidents 'days apart' you have either (if this is different, but similar position for more than one valve) a systematic failure after x hours in process, or (if repeated for one valve after repair) already weakened components not changed, contributing to new failure.

The cause of failure for ball-valves with actuators, not including failures of the actuators itself, is most often wear of sealing, often given by extreme fluid conditions with abrasive actions and deposits.

A 'normal' failure sequence is, depending on application, somewhere between three months and factory's lifetime, average perhaps 1-3 years up to 10-25 years.

Both type of repeated failures will show you nothing but weak, not correctly selected and/or supported equipment for your purpose. 'Tilted stem' may be caused by heavy weight, but also tells you that some of the stem construction or bearing is too weak.

Sidewise mounting can contribute to abrasive wear of sealings/bearings for the stem.

Check that the ballvalve you use have solid stem bearing, solid stem, supported with bearings top and bottom, extra sealing rings to prevent fluid reaching the stem bearings etc. In addition check that the supplier says OK to sidewise mounting, preferably with references,and this in addition to aligned support for pipeline, valve and actuator.

Note: a too stiff connection between actuator and valve, can give stem and bearing/sealing damage if unlinear forces occur.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close