Packing system and diagnostic method for a packing system of a valve assembly

A valve assembly comprising:

• a valve body including an inlet, an outlet, and a flow passage extending between the inlet and the outlet;
• a bonnet mounted to the valve body and having a bore that opens into the valve body;
• a stem extending through the bore and operatively connected to a control member arranged in the flow passage, the stem being configured to move the control member between a closed position and an open position to control flow through the flow passage;
• a first packing arrangement arranged in the bore about a first portion of the stem;
• a second packing arrangement arranged in the bore about a second portion of the stem, the second packing arrangement being downstream of the first packing arrangement along a leakage flow path through the bore;
• and
• a bore port extending through the bonnet to provide fluid communication between (i) an inter-packing location of the bore that is between the first packing arrangement and the second packing arrangement, and (ii) the outlet of the valve body;
• wherein the first packing arrangement is configured to, during normal operation, passively leak at a first leakage rate that is greater than a second leakage rate of the second packing arrangement, for a given pressure drop, when the control member is in the open position.

A method of evaluating a seal provided by a packing system for a valve, with respect to a leakage flow path from the valve that extends between an area of system pressure for the valve and an exterior of the valve, the method comprising:

• determining a rate of increase of an inter-packing pressure, the inter-packing pressure being a pressure of an inter-packing volume that is along the leakage flow path between an upstream packing arrangement and a downstream packing arrangement of the packing system, the upstream packing arrangement configured to, during normal operation, passively leak at a first leakage rate that is greater than a second leakage rate of the downstream packing arrangement for a given pressure drop;
• determining a reference pressure at a reference location that is downstream of the inter-packing volume along a sensing flow path, the sensing flow path providing fluid communication between the inter-packing volume and an outlet of the valve;
• and
• calculating a leakage rate of the upstream packing arrangement of the packing system based on the rate of increase and the reference pressure.