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

416 Centrifugal Pumps: Design and Application
Figure 17-54. Wear of hard seal faces from an environment with poor lubricant.
sealed was ethane at 1200 psig and 3600 rpm. These hard seal faces offered
no additional lubricant from the materials of construction. This
problem was solved by using a mechanical grade of carbon with hydropads
running against a tungsten carbide mating ring.
Poor lubrication can also be a problem on higher temperature applications.
Figure 17-56 illustrates the results of operating a metal bellows
seal on or near its atmospheric boiling point. Note the large amount of
wear on the tungsten carbide surfaces. This also resulted in seal face vibration
being transferred to the bellows, causing a leak at that point. This
problem was corrected by lowering the temperature in the stuffing box to
50° below the liquid's atmospheric boiling point. Another solution is to
consider the possible use of double opposed metal bellows seals with a
good lubricant between the seals. Double seals, when properly applied,
can last 2¥2 times longer than single seals on high temperature applications.
Corrosion of seal parts can be a serious problem that will appear over a
longer period of time. Corrosion may not be isolated to just one structural
part of the seal, but may be common to all parts of the assembly.
Carbon materials can become gray, appear to be porous, and lose their
hardness. Metals such as tungsten carbide, as shown in Figure 17-57, can
have their binder etched out. In this case, once the corrosion covers the
entire seal face, leakage occurs. Material selection should be made care-