Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Table 21-2
Causes of Seal Failures
Mechanical Seal Reliability 559
Operating problems 30% to 40%
Improper installation 20% to 30%
Pump design/repair 10% to 20%
Misapplied seal 10% to 20%
Worn out 1% to 5%
Miscellaneous 15% to 20%
Total 100%
ply selecting the proper seal, installing it correctly, and operating the
pump carefully.
Seal Hardware Failures
Another way to look at seal reliability is to insist that the seal must
survive in spite of any problems with the pump or its operation. In this
case, failures are examined from a hardware or design point of view. In
other words, if a pump requires repair because the seal is leaking, the
corrective measures are directed towards the seal hardware. This may
not always be correct; however, the statistics presented in Table 21-3
seem to apply to hardware failures in refinery and chemical plant pump
seals. Naturally, seals or pumps that were not properly installed or repaired
are omitted from Table 21-3.
Table 21-3
Mechanical Seal Hardware Failures
Rotating or stationary face 40% to 70%
Loss of axial movement (hangup) 10% to 20%
Fretting 10% to 20%
Corrosion 10% to 20%
Miscellaneous 5% to 20%
Total 100%
Seal Faces. Table 21-3 shows that, in pump repairs caused by hardware
failures, the seal faces are the apparent problem 40% to 70% of the time.
These faces were severely worn or damaged. In some instances, an immediate
improvement was made by simply changing face materials. For
example, a stellite or ceramic face might be replaced with a solid tungsten
carbide face. In other instances, the face materials could not be
changed or improved and efforts were focused on other areas.