Dry Gas Seal Damage of Compressors – Fully Explained!
According to differences in sealed medium, medium pressure and operating speed, compressor dry gas seals are classified into single dry gas seals, double dry gas seals and tandem dry gas seals.
Single dry gas seals are applicable to working conditions where minor leakage of process gas to atmosphere poses no hazard, such as CO₂ compressors, air compressors and nitrogen compressors.
Double dry gas seals are adopted for conditions where process gas leakage to atmosphere is prohibited, while nitrogen ingress into the unit is permissible. This applies to dirty or unstable process gas, or hazardous negative pressure conditions.
Tandem dry gas seals are used for scenarios allowing slight process gas leakage to atmosphere. They adopt a two-stage tandem configuration: the primary stage serves as the main seal and the secondary stage acts as standby seal.
Under normal operating conditions, the primary seal bears all or most of the pressure load, while the secondary seal bears little or no pressure drop. Process gas leaking through the main seal is diverted to the flare for combustion. A tiny fraction of process gas passes through the secondary seal and is vented to a safe area. The secondary seal provides backup protection in case of primary seal failure.
Common Causes of Damage
(1) Reverse rotation of unidirectional grooves or low-speed operation
Improper installation may lead to reversed assembly of drive end and non-drive end. In addition, unavoidable reverse rotation during unit shutdown and low-speed warming-up operation can damage the seal. In severe cases, the seal ring will fracture directly.
(2) Failure of rear isolation seal leading to contamination of outer seal
Design defects or improper operation may cause lubricating oil to contaminate seal faces, including poor venting of bearing housing (clogged breather filter), insufficient gas flow due to low designed gas velocity, improper number of labyrinth teeth or clearance, undersized orifice plate, system control faults, nitrogen pressure fluctuation or supply interruption, incorrect startup/shutdown sequence and misoperation.
(3) Failure of front labyrinth seal of compressor resulting in seal contamination
(4) Improper handling during startup and shutdown leading to seal contamination
During startup and shutdown, stable flow of primary seal gas is hard to maintain, and gas inside the compressor may flow backward and contaminate the primary seal face. Therefore, relatively high leakage often occurs at low pressure during initial pressurization.
Before pressurizing the unit for startup, startup seal gas must be injected via the control system to prevent backflow of process gas and seal contamination. During shutdown, gas supply shall be switched timely to avoid reverse flow of process gas. Seal contamination shall also be prevented during the shutdown period.
(5) Failure of filtration system under normal operation leading to seal contamination
The filtration system may fail for the following reasons, resulting in seal contamination and breakdown: excessive liquid entrainment in seal gas exceeding filter capacity; delayed switching of clogged filters leading to filter element rupture; massive fine particles smaller than the filter precision entering the system. Although each particle size falls within filter tolerance, the large total quantity will damage the seal and associated systems.
(6) Seal failure induced by unit malfunctions
During normal operation of a carrier gas compressor in a chemical plant, unit vibration surged rapidly beyond instrument measuring range, followed by excessive seal leakage. After disassembly inspection, the rotating seal ring was found fractured. The root cause was loosening of the hot-fitted balance disc on the main shaft, which triggered axial displacement, contact and abrasion with stationary components. This caused excessive vibration beyond the bearing capacity of the dry gas seal and finally seal damage.
Single dry gas seals are applicable to working conditions where minor leakage of process gas to atmosphere poses no hazard, such as CO₂ compressors, air compressors and nitrogen compressors.
Double dry gas seals are adopted for conditions where process gas leakage to atmosphere is prohibited, while nitrogen ingress into the unit is permissible. This applies to dirty or unstable process gas, or hazardous negative pressure conditions.
Tandem dry gas seals are used for scenarios allowing slight process gas leakage to atmosphere. They adopt a two-stage tandem configuration: the primary stage serves as the main seal and the secondary stage acts as standby seal.
Under normal operating conditions, the primary seal bears all or most of the pressure load, while the secondary seal bears little or no pressure drop. Process gas leaking through the main seal is diverted to the flare for combustion. A tiny fraction of process gas passes through the secondary seal and is vented to a safe area. The secondary seal provides backup protection in case of primary seal failure.
Common Causes of Damage
(1) Reverse rotation of unidirectional grooves or low-speed operation
Improper installation may lead to reversed assembly of drive end and non-drive end. In addition, unavoidable reverse rotation during unit shutdown and low-speed warming-up operation can damage the seal. In severe cases, the seal ring will fracture directly.
(2) Failure of rear isolation seal leading to contamination of outer seal
Design defects or improper operation may cause lubricating oil to contaminate seal faces, including poor venting of bearing housing (clogged breather filter), insufficient gas flow due to low designed gas velocity, improper number of labyrinth teeth or clearance, undersized orifice plate, system control faults, nitrogen pressure fluctuation or supply interruption, incorrect startup/shutdown sequence and misoperation.
(3) Failure of front labyrinth seal of compressor resulting in seal contamination
(4) Improper handling during startup and shutdown leading to seal contamination
During startup and shutdown, stable flow of primary seal gas is hard to maintain, and gas inside the compressor may flow backward and contaminate the primary seal face. Therefore, relatively high leakage often occurs at low pressure during initial pressurization.
Before pressurizing the unit for startup, startup seal gas must be injected via the control system to prevent backflow of process gas and seal contamination. During shutdown, gas supply shall be switched timely to avoid reverse flow of process gas. Seal contamination shall also be prevented during the shutdown period.
(5) Failure of filtration system under normal operation leading to seal contamination
The filtration system may fail for the following reasons, resulting in seal contamination and breakdown: excessive liquid entrainment in seal gas exceeding filter capacity; delayed switching of clogged filters leading to filter element rupture; massive fine particles smaller than the filter precision entering the system. Although each particle size falls within filter tolerance, the large total quantity will damage the seal and associated systems.
(6) Seal failure induced by unit malfunctions
During normal operation of a carrier gas compressor in a chemical plant, unit vibration surged rapidly beyond instrument measuring range, followed by excessive seal leakage. After disassembly inspection, the rotating seal ring was found fractured. The root cause was loosening of the hot-fitted balance disc on the main shaft, which triggered axial displacement, contact and abrasion with stationary components. This caused excessive vibration beyond the bearing capacity of the dry gas seal and finally seal damage.
