Fluid rarely flows from lower pressure into higher pressure. So, no, it is not likely that you could contaminate the process with barrier fluid as long as the seal chamber pressure is higher than the barrier fluid pressure. But, as the old saying goes, “Never say never.”
Earlier today, we were examining a repeat failure of a tandem seal with a Plan 52. The inner seal stationary face was popped out of position and cocked in the housing. We found that the operators were filling the seal pot with fluid using a pump that pumps the fluid into the bottom of the pot. They were performing the initial fill of the pot with the top vent on the pot still blocked in to flare. When they filled the pot from empty to normal level, pressure was building in the pot higher than the static pressure in the pump case and some of the barrier fluid was forced into the process, pushing the mating ring out of its fit.
We have only started using pressure pumps to fill our seal pots from the bottom in the past few years. Before that, operators would open a plug on the top of the pot and pour in the barrier fluid using a funnel. Because of concerns with exposure to flare gas, we converted our pots using quick-connect fittings on the bottom connection and set up carts in the control room so that they can add barrier fluid under pressure without removing that top plug. This is safer for the operators and allows them to add barrier fluid even if the pump is running. But, we did not initially realize that the method of adding barrier fluid now has the potential to build pressure in the seal pot if they add fluid when the vent to flare is blocked in.
Johnny Pellin
