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Derek Brown

Pump duty/stand - by arrangement

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Posted (edited)

Hi there,

I was looking for peoples opinion on the duty/st-by arrangement for pump sets. I have not long started at a large petrochemical plant and to my surprise they do not do a periodic swap over of pumps as the Ops team have their “favourites”.

I am now looking to convince them otherwise and introduce an Ops routine in the CMMS to try and push them to do it. My question is has anyone ever encountered this and how did you overcome it, and also what was your strategy? For me having two pump sets with the same run hours is not ideal and should have a lead/lag machine where the lag is only used in times of inspection, overhauls or breakdowns until the lead unit can be brought back online.

Thanks

Derek 

Edited by Derek Brown

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Hi @Derek Brown building up equal run hours on both machines is indeed not a great idea in my opinion as you run the risk that age-related failure modes occur on both machines around the same time and potentially within the time it takes to get one pump returned back to service, then you end up with both out at the same time. 

If you explain the above carefully, I've found that it is usually not too hard to convince operators that they need to build a differential in run hours by for example running pump A 2 or 3 times as long as pump B.  And I have indeed in the past set tasks like this up in the CMMS to make sure it happens. We did this for rolls-royce turbines offshore and ran one for 2 months and then the other for 1 month with the idea to increase the run hour differential. The 1-month difference in run duration was all that we could get roll-royce to accept without having to apply preservation to the machine that was not running for that 1 month.

Also, you could consider using your control system to initiate this, with the control room operator only having to accept that the system can change-over pumps.

The other alternative is to run a real duty-standy whereby the standby only runs when the duty is under maintenance or has failed... but this is much harder for most people to accept and you then really need to make sure you set up your maintenance regime in your CMMS accordingly as you will need to test the start of the standby pump for hidden failures and need to think about preservation requirements for the machine that is not running for pro-longer periods.

 

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Hi @Erik Hupje,

 

Thanks for your response.

I think it prudent to mention the number of start/stops will also have an effect on seal life, and with condition monitoring fitted, should negate the need for time base maintenance and prolong the service life between overhauls. The  strategy for the least number of starts operating in a duty/st-by arrangement I think would prove to be the best for lower maintenance and downtime.

I suppose the two issues to consider are uptime and costs. 

Alternate or duty/st-by policies both have their pro's and cons and in term of reliability for either depends on their operating context and age related failures would be evident for a machine that is running and a machine that is not.

 

Cheers

Derek

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