Suction Header with two different elevations

[Khansahib]

In a production facility, the existing Overhead suction header (elevation: 9 ft) needs to be extended to accommodate two new pumps. The new pumps are bigger in size and to accommodate the valves and fittings the extended header is to be elevated by two feet (elevation: 11 ft). In other words the suction header will be 50% 9ft and 50% at 11 ft elevation. I have a feeling that the elevated header may develop gas pockets that can cause problem for the new pumps. The same case is with discharge header, which goes to metering skid. Your comments please

 

[ash9144]

I'm not sure how you're system is set up. But as long as you maintain enough liquid in the vessel you are pumping out of to meet NPSHr of the pumps it doesn't matter how high the suction is.

 

[pennpiper]

I would consider adding an equalizer line frop the top of this new high point, stepping this new line up back to a higher nozzle on the suction vessel. Maybe the Vent connection?

 

[pmover]

just curious, it is possible/feasible/practical to elevate the entire suction header? any restrictions, other than the additional pipe &/or fittings? Seems that if you can extend and elevate an additional suction header, the existing can be modified somewhat to match the proposed suction header.

Is the suction header the high-point in elevation of the system? It may be necessary to vent the higher suction header to avoid any entrainment of air into pumpage (if this is a concern).

are there any issues to address about balancing the flows with/without the 2 different suction header elevations through each pump (assuming parallel operation)? Without knowing flows and pressures, this may very well be a primary concern.

something to think about . . .

good luck!
-pmover

 

[Khansahib]

Ash, The upper deck has separator whereas the suction header and pumps are at lower deck. Logically, it is true that the line will be filled with liquid but in a production facility there are possiblities of gas break out (paticularly in three phase system. Although the separator and suction header will be operating at 120 psig whereas discharge at 220-240 psig but a little pressure variation in suction header may cause gas to break out and therefore to avoid that possibility I would be in agreement with pennpiper.

pmover, It would have been great to make a new Header and set at new elevation but there are number of constraints w.r.t prodution, time, space and welding etc. To your second point, NO the header is not at the the high-point in elevation of the system. In response to third point, there is no balancing problem but in an offshore plateform one alway have sapce problem and system shutdown is a big hue and cry.....

Thanks gentlemen for your valued input.

 

[rzrbk]

You may not have a problem with gas pockets depending on the type of pump.

The pump Centerline should be kept at or above the suction line, with suction pipe flat or continuously rising. This will be easy to do with an end-suction pump, but not with some types of between bearing pumps.