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In Piping Plan 75 there is a containment seal chamber leakage collection system for condensing or mixed phase leakage on Arrangement 2 seals. This plan is used when pumped fluid condenses at ambiente temperatures. This system is supplied by vendor.
Piping Plan 75 systems are typically used on Arrangement 2, unpressurized dual seals, which also utilize a dry containment seal and where the leakage from the inner seal may condense. They may be used with a buffer gas (Piping Plan 72) or without a buffer gas (Piping Plan 71).
If an unpressurized dual seal is installed, usually it is because leakage of the pumped fluid to the atmosphere should be restricted more than can be achieved with an Arrangement 1 seal. Therefore, a means is needed to collect the leakage and route it to a collection point. The Piping Plan 75 system is intended to perform this collection function for pumped fluids that may form some liquid (condense) at ambient temperature.
NOTE Even if the pumped liquid does not condense, users may wish to install this system because of the risk of back-flow of condensation from the collection system.
Piping Plan 75 is intended to work as follows. Leakage from the inner seal is restricted from escape by the containment seal and routed into the drain line. The collector accumulates any liquid, while vapor passes through into the collection system. A level indicator on the collector is used to determine when the collector needs to be drained and the level transmitter will enable the user to monitor the liquid leakage rate. An orifice in the outlet line of the collector restricts flow such that high leakage of the inner seal will cause a pressure increase and trigger the pressure transmitter to alarm at a gauge pressure of 0.07 MPa (0.7 bar) (10 psi). The block valve in the outlet of the collector serves to isolate the collector for maintenance. It may also be used to test the inner seal by closing while the pump is in operation and noting the time/pressure buildup relationship in the collector. If specified, a connection on the collector may be used to inject nitrogen or other gas for the purpose of testing the containment seal.
The pressure transmitter in Piping Plan 75 will track the pressure in the vapor collection system. In normal operation, the pressure in the containment seal chamber can be as high as the vapor collection system pressure plus the check valve cracking pressure (if present). Pressures greater than this may indicate excessive leakage past the inner seal.