A newsletter on pumps and reliability
July 2005
Do you Know
What's in Your
Seal Reservoir?
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Many pump in industrial applications utilize dual (double or tandem) mechanical seals. The barrier or buffer system that supports this type of seal frequently includes a reservoir. These reservoirs provide volumetric storage for the barrier or buffer fluid. They also frequently include an integral cooling coil to facilitate removal of heat generated by the mechanical seal. However, seal reservoirs sometimes become a collection point for contaminates and wear products. In this issue we will relate a field experience with this problem that demonstrates how a lower initial cost welded reservoir may be more costly over its lifetime than its initially more expensive flanged counterpart.
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Dale B. Andrews - Editor |
Printable Version |
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Recently, one of our field service engineers called on a major petrochemical plant in Thailand to assist in rebuilding a large API process pump that had experienced a bearing failure. The pump is equipped with a double mechanical seal, an API plan 53 pressurized reservoir with an integral cooling coil, and a shaft driven circulating device to circulate oil between the reservoir/cooler and the mechanical seal. The bearing failure resulted in severe damage to the mechanical seal, such that the seal also required replacement. The following are excerpts from the engineer’s trip report.
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Welded Reservoir
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...Upon flushing of the seal reservoir for P2202 primary seal, it was noticed that the effluent oil was black and full of what appeared to be metal and carbon. Subsequent flushes failed to clear the oil. The reservoir was sent back to the shop to be re-cleaned by steam flushing.
Once assembled, filling and flushing of the primary seal system began. Unfortunately the primary seal reservoir continued to have debris come from it. Several gallons of oil were used to flush the reservoir but it would not produce a clean oil sample...
It is decided to send the reservoir out for cleaning by hydro-blasting...
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...the Hydro-blasting is not successful in removing the dirt and debris from the primary seal reservoir. It is decided to cut open the reservoir for a manual cleaning and then welding, X-ray and Hydro-test.
...At 11:30 the dirty oil reservoir is opened for inspection. The inside is exposed. All surfaces have a 3 mm coating of metal, carbon and other material.
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Debris coated
reservoir
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As the seal failed, debris circulated through the seal support system. Lower fluid velocity in the reservoir allowed solids to plate out on the internal surfaces of the cooling coil and the seal reservoir. The size and position of the cooling coil hindered effective pressure washing or steaming. The seal reservoir, in this case, is an ASME code stamped vessel. Cutting open the reservoir for inspection and manual cleaning was a time consuming and costly event. Even more costly was the 24 hours of lost production while troubleshooting, cleaning and repairing the reservoir. This reservoir, and others in the same plant complex, have since been replaced with flanged reservoirs that allow access for inspection and cleaning. Flanged reservoirs are more expensive than their fully welded counterparts, but in this case anyway, the cost difference was insignificant compared to the total cost incurred to clean the fully welded unit.
 The service engineer easily detected the debris in the seal reservoir because of the severity of the seal failure. However, normal wear of the seal face over time will result in deposits of seal face material in the seal reservoir that might go visually undetected during a routine system flush prior to start up. This material, when entrained in the barrier or buffer fluid circulation stream, will likely cause an increase in the frequency of seal failures because of increased seal face wear and reduce cooling capacity. Internal inspection and cleaning of seal system reservoirs is an important part of periodic pump maintenance. If there is the potential for reservoir contamination at your facility, it may be worth considering flanged reservoirs from the standpoint of lower total cost of ownership.
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Flanged Reservoir
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