MTBF for "centrifugal" pumps
MTBF for "centrifugal" pumps
(OP)
I'm a Reliabiilty Engineer and working now in the refinery for 6 months. My question is how do Refineries calculate MTBF on their pumps? Do we need to count all installed pumps in equation or only Running pumps? For example in a Turnaround should I still count the pumps that are down in that paticular month? Any answer to my question would be appreciated .....





RE: MTBF for "centrifugal" pumps
It depends what you wish to achieve. My own view is that it is does not matter much provided that you are consistent. MTBF is best used for seeing whether you are improving or whether you are getting worse. In that case the base number of pumps is not a big issue unless you change part way through. If you wish to compare yourself with another user, it is good to use their definition.
On our chemical site we use all installed pumps on the grounds that when they are installed they are subject to wear and tear from vibration, washing down, etc. Also we do not have a great number of installed spares.
There are a lot of other variations in definition for MTBF around what constitutes a failure. We get blockages and minor maintenance issues (we call interventions). If we clear a blockage and don't overhaul the pump we do not count this. We overhaul some pumps routinely but most predictively. We count all overhauls of these sorts as "failures" for our monitoring on the grounds that the predictive pull is for an incipient failure and if there were no degradation mechanism we would not be doing routine overhaul. Other people have different conventions.
Another issue is that there is a variation in standard of what people will accept as a running machine. Does a minor barrier seal fluid leak cause you to pull a pump? Depending on your standards you get different unit lives.
RE: MTBF for "centrifugal" pumps
The exception would be if it was possible for non-running pumps to fail e.g. in a highly corrosive environment.
RE: MTBF for "centrifugal" pumps
Also you may find in some (particularly in corrosive) environments, that the less a pump runs, the lower the MTBF.
RE: MTBF for "centrifugal" pumps
RE: MTBF for "centrifugal" pumps
If that is not feasible, there are other recommended methods to help out in prolonging the MTBF, among them:
-reduce impeller diameter;
-install by-passes;
-have speed-controlled drivers;
-control flow rates with automatically operated valves;
-put holes thru impellers to equalize pressures.