Selection criteria and recommendations for mechanical seal isolation fluids

It is described in the API682 mechanical seal flushing standards

Could you send API682 to my email? I couldn’t find it

The recommended materials listed in Table 10 of Appendix A of API682, for shaft seal systems in pumps (suitable for centrifugal pumps and rotor pumps) – Selection of blocking/buffer fluids. Table 10: The following factors should be considered when selecting a blocking/buffer fluid: a) The compatibility of the fluid with the fluid being pumped, so that no chemical reactions occur, or gelation or precipitation does not take place, in the event that the blocking/buffer fluid leaks into the pumped fluid or vice versa. b) Compatibility of the fluid with metal parts, rubber components, and other materials in the sealing/flushing system. In pressurized blocking fluid systems that use gas layer pressurization, special attention must be paid to the application conditions and the selection of the blocking fluid. As temperature and pressure increase, the solubility of gases in the blocking fluid increases; when the pressure is reduced or the temperature is lowered, the gases are released from the solution, forming bubbles that cause losses in the circulation of the blocking fluid. This problem often occurs in highly viscous, clogging fluids, such as lubricants used at pressures above 10 bar. The viscosity of the blocking/buffer fluid over the entire operating temperature range must be checked; particular attention should be paid to the viscosity at startup, with the viscosity at the lowest temperature being less than 500 mm2/s. a) For operating conditions with a working temperature above 10°C, hydrocarbon blocking/buffer fluids with the following viscosity levels perform well: a viscosity of less than 100 mm2/s at 38°C ； At 100°C, the viscosity is between 1 and 10 mm2/s. b) For operating conditions with a working temperature below 10°C, hydrocarbon blocking/buffer fluids with the following viscosities perform well: a viscosity of 5–40 mm2/s at 38°C ； At 100°C, the viscosity is between 1 and 10 mm2/s. c) For aqueous fluid streams, a mixture of water and ethylene glycol or propylene glycol can be used; automotive antifreeze should not be used. Antifreeze additives tend to accumulate on seals, and can cause seal failure due to gelling. d) The fluid shall not freeze at the lowest ambient temperature at the site. Atmospheric leaks caused by volatile and toxic fluids, or the measures taken to address them, must not cause pollution to the environment. a) The initial boiling point of the fluid should be at least 28°C higher than the ambient temperature. b) In the presence of oxygen, the flash point must be higher than the operating temperature. c) When used as a blocking fluid, ethylene glycol can be considered a hazardous substance/hazardous waste. The fluid must be able to maintain a sealed state and operate continuously for over three years without deteriorating, and it must not produce any sediment, polymers, or carbon deposits after use. a) For hydrocarbon fluids, high-purity paraffin oil or synthetic oil without anti-wear/anti-oxidation additives yields good results. b) The anti-wear/anti-oxidation additives in industrial turbine oil will deposit on the sealing surfaces.

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