Dry gas seal assembly

A compressor, comprising:

• a housing including a suction port and a discharge port;
• a shaft penetrating the housing;
• a centrifugal impellor fixed to the shaft and arranged for compressing a gas from the suction port to the discharge port;
• a seal assembly circumscribing the shaft near a location where the shaft penetrates the housing, the seal assembly comprising:
• a primary seal stage including a primary ring coupled to the housing and a mating ring coupled to the shaft, the mating ring formed of a brittle material;
• and
• a secondary seal stage coaxially positioned outside the primary seal stage and including a primary ring coupled to the housing and a mating ring coupled to the rotating shaft, the mating ring formed of a ductile material.

A seal assembly comprising:

• a primary seal stage including a primary ring arranged to be coupled to a housing and a mating ring arranged to be coupled to a rotating shaft;
• and
• a secondary seal stage coaxially positioned with respect to the primary seal stage and including a primary ring arranged to be coupled to the housing and a mating ring arranged to be coupled to the rotating shaft,
• wherein the primary ring and the mating ring of the primary seal stage are formed of materials chosen to effectively block flow of gas through the seal assembly, and
• wherein the primary ring and the mating ring of the secondary seal stage are formed of materials chosen to survive a failure of the primary seal stage.