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Centrifugal pumps alarms and trips

Centrifugal pumps alarms and trips

Centrifugal pumps alarms and trips

Hello everyone

I was wondering if there is any standard or recommended practice regarding typical alarms and trips to be implemented around centrifugal pumps?

The reason is: in the refinery I am working in, I see plenty of alarms and trips that I don't see the purpose.

For exemple, on pumps (canned motor pumps coming with their own winding TSHH) discharging LPG from debutanisers (gasoline HDT and catalytic reformer) to deethaniser, we can see:

- PDAH on suction filters (OK)
- PAL on suction (OK)
- TAH on suction (redundant with PAL on suction?)
- FAL in discharge (OK)
- PAL on discharge (why?)

- LSLL on suction drums (OK)
- PSLL on suction (OK)
- TSHH on suction (redundant with PSLL?)
- PSLL on discharge (why?)
- FSHH on discharge (redundant with PSLL on discharge? but maybe a better option?)

On other pumps, I have also seen PDAL and PDSLL (between pump suction flange and suction drum) to trip the pump on low NPSHA (similar to PSLL on suction)...

So could you please let me know your thoughts on that (I have indicated my comments next to the above items)?

I do understand that alarms and trips are selected on a case by case basis, but maybe there is a minimum set to implement, but I don't know where to find this information.


@Lionel_Sheiko / geniechimiquefacile.com

RE: Centrifugal pumps alarms and trips

The vendors of the canned motor pumps should be able to give you a preferred configuration for pump protection and the reasons for each device.

It is my understanding that high-temperature operation poses the largest threat to canned motor pumps, with run-dry and bearing failure being the second largest threats

I would consider the purchase of a packaged protective device devices available for these pumps. There are many advantages of a continuous monitoring system



Sr. Process Engineer

RE: Centrifugal pumps alarms and trips

IMO, the redundant of the pump alarms and shutdowns may be resulted form the HAZOP, AOA, and SIL requirements. Typically as the level identified per risk assessment matrix, it requires certain number of the safety measures in place to mitigate the potential risk. The additional alarm or shutdown may be required to satisfy the risk level as identified.

RE: Centrifugal pumps alarms and trips

Check the hazop worksheets and / or with the pump vendor if the PSLL on pump discharge will pick up some serious abnormality within the pump that the FSHH wont.

RE: Centrifugal pumps alarms and trips

"Is there a standard practice" - Not really.

Most of those you've listed are though pretty standard, but it depends on the process, size of pump, fluid, design pressures and temperatures etc.

What you're trying to do is protect the pump from damage if it sees fluid conditions outside it's operating envelope. So for a pressurized high vapour pressure liquid like you have , this includes low pressure ( liquid will boil and you'll get vapour in a pump not designed for it) and high temp ( again potential gas or damage to pump) or no or low flow which long term could damage the pump.

Whether you need them all and what levels they are set at should be addressed in a LOPA study or alarms review. The alarms study looks at whether there is sufficient time and warning for the operator to actually do anything if the alarm goes off before the unit trips. In an upset condition the controller can become overwhelmed with alarms and so their usage needs to be curtailed to those that actually are useful. Trips on the other hand work well in extremis and if set at the correct level shouldn't inhibit the process.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Centrifugal pumps alarms and trips


Discussing with the reliability guy, I have learnt that PAL and PSLL on discharge side aims at limiting flowrate above 10-20% of BEP. In fact, only PT were available on currect pumps when decision to install additionnal safety loops has been taken. So the choice to install PSLL instead of FSHH.

@Lionel_Sheiko / geniechimiquefacile.com

RE: Centrifugal pumps alarms and trips

Also, in many cases, a plant will adopt their own "standard" for protection logic of motors, pumps, etc. based on their own preferences (sometimes driven by HAZOP, internal lessons learned, or other considerations previously noted).

RE: Centrifugal pumps alarms and trips

As you've already identified there lots of things to monitor and protect pumps...

Our preference is always power monitoring (true power) so that as soon as process upset happens for whatever reason, then immediately the power will change and once limits are set to within the minimum and maximum flow limits, the motor will trip as soon as these flow-rates are reached - for more info follow the link http://www.cdrpumps.co.uk/pump-protection/

As rule of thumb, low flow should be ideally more than 20% of the flow at BEP and no more than 10% past BEP - of course there is always flexibility but generally follow these rules and you will be safe !

Ash Fenn


RE: Centrifugal pumps alarms and trips

And don't forget that since there is a high likelihood that all the machinery and piping is insured, insurance companies also have requirements. So check them out.

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