I found the pump blocked-in with the discharge valve closed. Apparently the pump had been operated in this condition for long enough to overheat causing the sleeve bearings to melt. The bearing metal had flowed out of the bearing housing and dripped down onto the concrete pad. Finally the electrical over current protection opened the circuit and shut down the pump preventing any further damage.
As I investigated the incident, I found that most of the controls had been relocated from the field into the control room in the six months prior to the incident. This change allowed a number of the field operators jobs (who used to manually line up the pumps) to be eliminated. It turned out that this was not the first such incident. There had been a number of situations in which remote equipment was started without being properly lined-up. The old process that involved hands-on line ups had been replaced by one in which many of the critical conditions were obscured from the operator at the controls.
I also recall that at this same time the refinery was in the process of transitioning from four digit pump numbers (P-1234) to five digit pump numbers (P-12345). As a result, I was amazed when I found that the equipment number for this pump contained only three digits (P-123). The pump was more than fifty years old.
When I received the operator's write-up of the incident, they said that the pump probably failed because it was a chronic problem. They said they were "always" having problems with it. Checking the equipment files, I found that the pump had not seen the inside of a shop for more than thirty years. (If only all of our pumps were as big a problem.)
I learned a lot from that experience. I learned about the difficulties of changing long-standing procedures. I learned about just how reliable a piece of equipment can be when properly designed, operated and maintained. I also learned how fast that can change when any one of the key elements leading t the reliability is changed. I also learned how far perception can be from reality. Most of all I learned about the value of actually putting your eyes on something before forming an opinion or making a recommendation.
This story can be filed under a number of categories:
• Examples of how much things have changed.
• Examples of how much things have remained the same.
• Examples of the good old days.
• What engineers used to do before computers were invented.
My choice would be to file the story under the heading of how learnings from the distant past still apply to current day advancements in technology.
Using current technology and the process of Failure Mapping, we are able to perform a dramatically different level of remote diagnostics than was possible at the time of the story. The simple fact that it is possible to remotely determine that the pump is running but there is no flow would point to a number of possible diagnosis. Based on prior experiences with this Malfunction Report and the records of the Failure Modes used to close the file on those experiences, it should be possible to point to one of the following situations:
• Pump isolation valves - closed
• Strainer - plugged
• Impeller - worn
• Pump shaft - broken
• Pump Impeller - Spun from shaft
• Other
The fact that the system operated at the usual rate yesterday would suggest to the person performing the diagnostics that the problem is not a worn impeller. It is unlikely a pump with a worn impeller would go from full capacity to no flow in a single day.
If we make the assumption that our diagnostic choices are the result of several years of failure mapping and that there have been few or no cases of the impeller spinning off the shaft, we could also discount that possible failure mode.
So from our list, the likely possibilities are:
• Pump isolation valves - closed
• Strainer - plugged
• Pump shaft - broken
Knowing these possibilities are most likely, the remote diagnostician should instruct the operator to shut the pump down before any damage is done. Allowing the pump motor to continue to operate in any of these situations is inviting disaster.
Continuing to run a pump that is blocked in or has a plugged strainer will lead to the same kind of failure that occurred 40 years earlier or worse. Continuing to run a pump with a broken shaft can provide a source of ignition and result in a fire.
With the appropriate information coming from Failure Mapping files, a relatively accurate recommendation can be provided. To get any closer to the real cause, it is necessary to dispatch a troubleshooter to lay his hands and eyes on the actual situation.
In the case I described at the beginning of this article, on on-site visit (by either an operator or an experienced troubleshooter) would identify the closed discharge valve. Once the valve was opened, the pump was started and the system was allowed to operate under observation for a few minutes, the problem would have been solved without further interruption or expense.
If the troubleshooter found the pump was properly lined-up with both suction and discharge valve opened, he might check to see if a start-up strainer had accidentally been left in place. He might also rotate the shaft to see if it spun all too freely suggesting a broken shaft.
Conclusion:
You might ask yourself if your operation behaves more like the 40-year old example at the beginning of the article or more like the model described later in the article.
The model described later in the article depends on a number of key elements:
1. Data connecting typical Malfunction Reports (Lost Functionality - Specific Behavior) to typical Failure Modes (Defective Component - Condition).
2. Analysis of the statistics of the above data determining the statistical likelihood of each possible outcome.
3. Clear understanding of the role, responsibilities and tools available to the remote diagnostician.
4. Clear understanding of the role and responsibilities of the on-site troubleshooter.
When these elements are properly combined, your operation is more likely to behave like one functioning in the twenty-first century than one from 40-years earlier.
Article submitted by Daniel T. Daley
