Post from another section on PSV selection for PD pumps

[cannondale]

I'm designing a system to pump mud cuttings slurry and am looking for a pressure safety valve to protect the system.
The max working pressure is 520 barg and we plan to set the PSV at 572 barg (8294 psig). The pump is a triplex, 8" stroke 5.5" plungers, with a damper on suction and discharge to get me +-3% pulsation frequency.

Firstly is the set pressure too close to the duty point to prevent it going off under normal conditions?

Secondly i've been looking at auto reseat, lever reset and pilot operated valves. is there a technical reason why i shouldn't use the auto reseat over a lever reset?

Pilot operated valves are pretty much out due to cost, but I can't help but keep looking at the auto reseat valves on a price basis.

Plus, anyone know why I can't find valves at this pressure with PED certification.

Your comment greatly appreciated.

 

[Casimo5]

cannondale,

Regarding your set pressure/operating pressure, API 520 Part 1 shows the maximum expected operating pressure at 90% of your set pressure. Typically if you operate above 90% of your set pressure, you want to use a pilot operated valve to avoid leaking by. Your max working pressure is at 91% of operating pressure, so you're pretty close. The relief valve most likely will not go off during normal operating conditions, but you may have issues with leaking as time goes by.

As for your other questions, I am not familiar with the lever reset option. I'm only familiar with levers used on relief valves to manually cause them to lift. I thought all relief valves were auto reseat and that only devices like rupture disks and rupture pin valves did not automatically close. You may want to speak to a manufacturer about those options.

By the way, is this mud cuttings slurry a dirty service? Sounds that way. Have you considered a rupture disk? There are definitely some cost savings but you have to consider the effects of having a non-reclosing device in your system.

Casimo

 

[cannondale]

This is a slightly unusual scenario as the motor won't be able to achieve the psv pressure, at the duty flow anyway.
We have a fracturing duty of 6m3/hr @ 520bar and two production duties 66m3/hr @ 360 and 96m3/hr @ 240bar. The system will be controlled on the VSD somewhere below 800kw.
Our table shows constant torque at low speed and then tracks down a constant power curve, taking in the two remaining duty points. The PSV is only going to be protecting the system at the very highest pressure that they will likely use very intermittently.
The more fundamental issue is actual selection of a valve that will be fit for purpose.
Based on availability, I'd say almost everyone must be using auto reseat valves for system protection, unless there is some other motivation, and then they go for pilot operated valve (lots more expensive). Just found another lever reset valve (but likely to be the same valve rebadged)
Anyone with any field experience?