Standard Pump Piping Layout especially Min Flow Lines 1

[sshep]

My Friends,

I am looking for an industrial standard (hopefully API) for standard piping layout around pumps, especially the minimum flow lines.

In virtually every plant I have ever worked in, each pump (including spare) at a distillation tower bottoms (for example) has its own minimum flow protection. The normal sequence would be: suction line, pump, minimum flow branch, check valve, block valve, and the the common discharge piping. The minimum flow branch would include a check valve also. This arrangement of check valves and lines will stop backflow into the tower, or forward flow around the pumps through the min flow line. I hope you can visualize this good practice for now as I am sure most of you have seen it that way.

I am now facing a new plant where the design is a single minimum flow line shared by both pumps with with an RO. The min flow line comes from the common discharge piping. There is no check valves either forward of the min flow branch, or in the min flow line itself so material can flow out or in to the process from the tank farm or other downstream equipment. I think this design is lame, but the claim of the designer is that this is actually a common cost savings arrangement. I don't believe that! However, when I looked at our own company standards, there is little reference to minimum flow piping layout in any of our standard drawings. API STD 610 does not give any help on the subject either.

After more than 25 years I know what to expect for good pump layout, but wish for an industrial reference. Can anyone direct me to an API practice or any other recognized source which gives a standard piping layout for pumps, including minimum flow piping? Any help is appreciated.

best wishes,
sshep

 

[LittleInch]

I'm not aware of any standard as such as there are too many permutations and what suits one location won't suit another. However issues like you describe normally should be addressed during the HAZOP where you look at all permutations of operations and consequences of flow in the wrong place and time, but I guess you know that.

A diagram or schematic of your two arrangements would be good to make sure we all understand your post.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Latexman]

sshep,

Do you have access to Process Industry Practices (PIP)? If so, refer to REIE686 - Recommended Practice for Machinery Installation and Installation Design, Second Edition and REIE686A - Recommended Practice for Machinery Installation and Installation Design (Supplement to PIP REIE686/API RP686).

Some history. REEP004 - Guidelines for Piping Arrangements for Centrifugal Pumps was withdrawn in March 2012 and its contents incorporated into PIP REIE686A - Recommended Practice for Machinery Installation and Installation Design (Supplement to PIP REIE686/API RP686). I know REIE686A speaks directly to your question on parallel or separate minimum flow lines. It says they must be separate on parallel pumps.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[sshep]

Gentlemen,

Thank you for your replies. I tried to post a sketch- hopefully the link works.

Unfortunately a HAZOP is only as good as the experience of the people involved. Sometimes you get great results you feel confident in, and sometimes not so much. I work with great teams at the plant operations and commissioning team level, but we are often downstream of cost driven design decisions and forced to manage whatever configuration is thrown our way.

best wishes always,
sshep

 

[sshep]

Thanks Latexman for the good advice as always. You, LittleInch, and the other regulars have been very helpful to me over the last 10 years in this forum.

I can see PIP REIE686A on the IHS website, but it is not in my company subscription. More and more of my projects seem to be referring to PIP standards, so I am trying to get it added.

best wishes always,
sshep

 

[petrochemical87]

sshep,
I concur the first design is superior to the second, but I have seen several configurations in the plants where Ive worked in that have employed the second design. The second design is good enough to handle min flow requirements when atleast one of the pumps in running. Backflow should only occur when both of the pumps are stopped.

 

[TD2K]

I've seen both used and sometimes both in the same unit. The project I'm working on how is basically #1 but coming off downstream of the check valves, not sure why it was designed that way.

For a relatively low head pump and where there are no plans to routinely operate both pumps, I'm okay with option 2. If both pumps can operate in parallel then whether you are actually ensuring both pumps have minimum flow depends not only how the orifice was sized but also the slope of the curves and the differnetial pressure both are seeing given the piping hydraulics. For high head pumps where the pumps are not only expensive but the energy wasted across an RO isn't minor, I prefer a minimum flow loop or automatic recirculation valves if the fluid is clean for each pump.