Analysis of dry gas seal failure in compressors

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The structural types of compressor dry gas seals can be further divided into single-face dry gas seals, double-face dry gas seals, and tandem dry gas seals, depending on the type of medium to be sealed, the pressure of the medium, and the operating speed. The single-end face arrangement is suitable for situations where a small amount of process gas leaks into the atmosphere without causing any harm, such as in carbon dioxide compressors, air compressors, nitrogen compressors, etc ； The double-end face arrangement is suitable for situations where it is not allowed for the process gas to leak into the atmosphere, but nitrogen is permitted to enter the unit – for example, when the process gas is dirty, unstable, or there is a risk of negative pressure ； A series arrangement is suitable for conditions where a small amount of process gas is allowed to leak into the atmosphere. It employs a two-stage series configuration, with the first stage serving as the primary seal and the second stage acting as a backup seal. Under normal operating conditions, the first stage of sealing bears all or most of the load, while the other stage experiences no pressure drop or only a minor one. The process gas that leaks through the primary seal is directed to the flare for combustion, and the very small amount of process gas that remains is led through the secondary seal to a safe location for venting. When the primary seal fails, the secondary seal can serve as an auxiliary safety measure. ★Common causes of damage: (1) Reverse rotation of the one-way groove or operation at low speeds. During the use of dry gas seals, incorrect installation can lead to the drive end and non-drive end being installed in reverse order; during machine shutdown, situations such as reverse rotation and low-speed warm-up operations occur, which can cause damage to the seal, and in severe cases the ring may even break completely. (2) Failure of the rear isolation seal, with contamination of the outer seal. During use, the lubricating oil may contaminate the sealing surface due to design or operational reasons. Examples include: poor evacuation from the bearing chamber (clogged filter in the breather cap), insufficient gas flow due to a low designed gas velocity, inappropriate number of labyrinth teeth or gaps, an undersized orifice plate, system control issues, fluctuations in nitrogen supply or interruptions in gas supply, incorrect sequence of start-up and shutdown operations, and human error. (3) Failure of the pre-compressor labyrinth, leading to seal contamination. (4) Improper handling during startup and shutdown, resulting in seal contamination. During startup and shutdown, it is difficult to maintain a stable flow rate of air for the primary seal; as a result, gas can flow back inside the machine, causing contamination of the primary seal surface. Therefore, during the initial pressurization phase after startup, the pressure may be low and the leakage rate high. Before preparing the unit to start up and carrying out pressing, it is necessary to inject starting seal gas through the control system first, in order to prevent process gas from flowing back and contaminating the seals ； During the parking process, the gas supply should be switched over in a timely manner to prevent process gas from flowing back and contaminating the seals ； During parking, avoid seal contamination caused by operations or other factors. (5) During normal operation, if the filtration system fails and the seal becomes contaminated, severe liquid contamination in the seal gas can occur during the operation of the dry gas seal, exceeding the filtering system’s capacity to handle it ； The filter became clogged and was not switched out in time, resulting in damage to the filter element ； The gas source contains a large amount of fine powder whose particle size is smaller than the filtering capacity of the filters; this exceeds the filters’ ability to handle such particles. Given the large quantity of this powder, it can affect the seals and the entire system, leading to the failure of the filtration system and ultimately causing damage to the seals as a result. (6) Seal failure due to unit issues: During normal operation of the carrier gas compressor in a chemical plant, the vibration levels of the unit increased sharply and exceeded the measurement range of the instruments; subsequently, the seal leakage of the unit became excessive. Upon disassembly, it was found that the sealing rotating ring was fractured, mainly due to the loosening of the balance disk mounted on the main shaft, which caused axial displacement and led to contact wear with the stator. This resulted in an increase in the vibration levels of the unit, exceeding the limits that the seal could withstand, thereby causing damage to the seal. (7) On-site misoperation: In an ethylene compressor at a chemical plant, after the unit had been operating normally for about two years, the seals at both ends failed suddenly, with the seal rings being damaged. Upon investigating the cause later on, it was found that due to the low temperatures in winter, the operators, out of kindness, turned on the heater for the sealing gas; this sudden change in temperature caused the sealing ring to burst.