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

Mechanical Seal Reliability 561
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Solids build up here ^
Figure 21-1. Seal hangup from accumulated solids (courtesy John Crane Inc.).
with many different types of resin and metallic binders. Hardfaces include
both nickel and cobalt bound tungsten carbide, various silicon carbides
and other ceramics. Gaskets may be made from many materials including
graphite foil, Teflon, nitrile, Kalrez, etc.
It is most likely that a suitable set of materials may be found for even
the most corrosive seal environment. Still, while searching for those materials,
corrosion problems do occur. Even after the proper materials
have been found, the wrong material may be inadvertently substituted at
the next repair.
Other Problems. There are other hardware problems that occur in addition
to face damage, hangup, fretting, and corrosion. The most perplexing
problem occurs when there is no obvious damage. This often happens
when sealing light hydrocarbons. For these products, the liquid may
flash to a vapor between the seal faces. Since most seals are designed for
liquids, the resulting force imbalance from flashing causes the faces to
"pop open." The solution may involve changing the balance ratio or seal
type or installing an external flush that will not vaporize so readily,
Seal Failures from Installation Problems
Proper installation is so important that all seal manufacturers conduct
extensive training courses on how to install their seals correctly. Most of
the larger seal users have their own internal training courses as well.
Consultants are available to teach proper seal installation. Still, the statistics
show that 20% to 30% of all seal failures are caused by a poor or
incorrect installation. Many installation problems seem to stem from improper
assembly of seal components and internal misalignment.
Improper Assembly. A large refinery may use several different seal
types from four or five manufacturers. Some plants do not have techni-