2 replies to this topic

[NFA]

During start up in our plant we faced problem with 2 PSV as they popped up during normal operation (142 barg) whereas the relieve set pressure for the PSV's 155 barg. the set of action lead to this pop up was as follows
1- the control room operator opened the flow control valve to divert the flow from up stream pressure of 142 bar to down stream pressure of 81 barg and the flow accross the flow valve increased from zero to 130 mmscfd in 7 second time.
2- we have got 2 PSV's popped up, one in the up stream of the flow valve and the second on the down stream of the flow valve, but found that both of them popped at pressure almost 15 barg less than the psv set pressure.
3- the only change that observed was the sudden increase in the velocity.
My concern is that I would like to know is there any relation between the PSV and the energy (velocity) in other hand is the increase in velocity can lead to PSV pop up?

[kkala]

I think increase of velocity alone cannot result in PSV pop up, but water hammer can. Fluid is probably gas, yet at such high pressures (increased density) hammering can be sensible.
I assume that flow control valve (FCV) stem had some oscillation, which caused water hammer on the upstream pipe. Though it is not easy (for me) to explain how hammer passed downstream of FCV, I suppose the upstream pressure wave reflected and passed through the open FCV to pop up the downstream PSV, set at (about) 95 barg.
Local pressure on a given pipe section increases instantaneously as pressure wave is traveling along it, and again when coming back by reflection; this could explain pop up of PSVs.
This is a personal interpretation, practical experience on both control valves and water hammer could give a better explanation to be welcomed.

Edited by kkala, 27 November 2012 - 06:41 PM.

[S.AHMAD]

1. Concur with kkala comments that the increase in flowrate has no effect on the popping of the PSV.
2. It seems that the control valves are design based on blocked discharge
3. Hammering is normally due to quick closing of downstream valve, but in you case it is opening of downstream valve. Therefore, popping due to hammering is unlikely.
4. I suspect that the spring pressure is lower than what it should be. So, I suggest that you recheck the PSV spring pressure.

Edited by S.AHMAD, 02 December 2012 - 09:53 PM.