Overview

As mentioned numerous times throughout this book, the running gap between the primary and mating gas seal rings is only a few microns, approximately 1/20th the diameter of a human hair. Contamination from solid or liquid material is the leading cause of dry gas seal damage and failure during operation, and is, therefore, the leading cause of reduced gas seal reliability. The introduction of foreign material into the running gap can cause the seal to leak excessively, and, if allowed to continue, eventually fail. When foreign matter is ingested into the running gap of the seal, the shearing forces between the primary and mating rings will increase. The seal components will overheat, eventually leading to some form of mechanical seal failure such as o-ring deterioration, cracking of the mating ring, and others. Some seals can fail catastrophically, fracture into many pieces, and even damage the compressor shaft or head. Silicon carbide is a more brittle material than tungsten carbide, and has been known to fracture into many pieces on failure. Some users avoid the use of silicon carbide solely for this reason.

There are four primary means of gas seal contamination (fig. 8-1):

1. Contamination from process gas. This type of contamination is possible when the pressure or flow of the injected sealing gas is insufficient to overcome the process gas (reference) pressure inboard of the dry gas seal, allowing untreated process gas to come into direct contact with the seal ring faces. Contaminants, which are sure to exist within...