Page 197 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 1 83

• Contamination. Gas contaminated by foreign material, such as welding
beads, sand, pipe scale, rust, and catalyst will also cause rapid wear.
• Improper break-in. Break-in can be a source of rapid wear if the rings
are improperly worn-in and a burnished rubbing surface is not
obtained. If this condition exists, the rings may continue to wear until
a burnished condition is conceivably achieved at some later date.

Causes of Abnormal Wear of Teflon Packing Rings

Because Teflon is widely used as a packing ring material, certain pecu-
liarities in its operating characteristics should be understood. While the
same conditions that cause abnormal wear in metal packing rings apply to
Teflon, there are certain additional phenomena that should be understood.
It must be understood that because of the self-lubricating properties of
Teflon materials, they will run completely without external lubrication or
they will run as any lubricated material requiring a bare minimum of
lubricant.
When operating without lubrication, the rings will lay down a coating
on the mating surface of the piston rod and, once established, will permit
the packing rings to run on this film at very low rates of wear and fric-
tion. When operating with lubrication, this film is not established unless
the lubricant is completely withdrawn. If oil is introduced after this film
has been established, it will displace the Teflon on the piston rod and the
rings will operate as lubricated ones. If the lubricant is then withdrawn,
the rings again establish a Teflon film on the mating piston rod surface.
During this coating period, high wear rates of the packing rings will be
experienced. It can be seen that conditions which cause a succession of
lubrication events alternating with periods of operation without lube oil
will severely curtail ring life.

Leakage

It is apparent that wear itself is not the root cause, but rather, a mani-
festation of one or more problems. Leakage, on the other hand, can be
both a by-product and a problem in itself.
Leakage can be caused by one or more of the following:

• Wear can be the most obvious cause of leakage. Complete wearing
out of the rings and failure to compensate for additional wear would,