What is severe service ? some of you may ask, most of the answer would be corrosion service, desalted water service, sandy service, high temperature or cryogenic etc, yes,those are examples for severe service, but could the low pressure water be severe service too ? yes, the answer is " it could".
Common maintenance staff or media could be considered “severe service” if some valves are not able to cope with it. For some people running a marathon is no problem, but for most it would be impossible without proper training and preparation for it.
If the valve is not prepared for that long time operation,it would be severe service for the valve. A ball valve class 900 from one of our customer's old valve, which was installed in produced water with some sand, the valve was working for years without problems under non-severe conditions, then one day the valve was used as a throttling valve for some hours and came under high DP conditions.pls check the result out from the pistures as bellow :
The Ball The Body
When throttling the valve, it came under extreme conditions due to the abuse of the ball valve. This ball valve is fine for opening with DP or closing in flowing conditions, but it is a stretch to use it as a throttling valve with 80 bar DP with two-phase and some sand. This was a standard condition that turned severe due to improper knowledge from the operator. The result of this was a heavy external leak with oil and water and ultimately, a shutdown of the installation.
Another case is a conventional trunnion ball valve with soft seat insert, the ball valve was in gas service with a system pressure of 130 bar, material 316 and PTFE insert in the seat as illustrated. Nothing severe until the operator decided to open the valve with 100% DP, and as one can understand he did not fully open the valve at once due to down stream equipment. But as any good operator would do, he carefully opened the valve to pressure up on the down stream side; but again, a standard valve in a severe condition for that valve.
One should be careful to open a soft-seated ball valve with DP and especially at 130 bar. There is a rule of thumb: you should not open a soft seated valve with a DP higher than 20 bar. In fact, 20 bar can be too much already if the valve is put into a 15% open position for several hours. A standard metal/metal-seated hard faced ball valve or gate valve should not be opened with a DP above 60 bar. Of course it depends on the media, the time used for throttling, etc.,
We do understand that in some cases, like a refinery with raw oil cooking at 560 degree Celsius, they don´t install fittings and add leak points as the media is self-igniting. they do not want an external leak. Back to the analogy of marathon running: you may train yourself to become a marathon runner or an ultra-marathon runner, but you can’t train a valve to become a severe service valve.
