Gate Valve Stem Packing Leak (Fugitive Emission)

Root Causes

Step-by-Step Repair Guide

1. 1

   Attempt in-service gland tightening first

   With the valve in service (depressurize only if company procedures require it for the specific fluid), tighten the gland follower nuts by half a turn increments using a calibrated torque wrench. Alternate between the two nuts to maintain equal load. Wait 5 minutes between increments and re-check leakage. Many packing leaks on graphite-packed valves can be stopped by retightening without repacking. Do not exceed the manufacturer's maximum gland torque.

   Never re-tighten gland on a valve under pressure if the fluid is flammable, toxic, or above 200 degrees C. Follow site permit-to-work procedures.

   Mark the gland nut position with a felt pen before tightening to measure how much you have tightened.

2. 2

   If retightening fails, plan for repacking under isolation

   Raise a work order and LOTO permit. On OS&Y gate valves with a backseat, the valve can be repacked under line pressure by opening fully to seat the backseat (which seals the gland from line pressure). Verify the backseat integrity by testing with the gland completely loose. If the backseat is sound, proceed to repack with valve fully open and process pressure on. If backseat is not sound or valve design does not have a backseat, full isolation is required.

   The backseat method only works when the backseat is confirmed intact. Never assume backseat integrity without testing.

3. 3

   Remove the old packing

   Back off the gland follower nuts and remove the gland follower. Use a packing extraction tool (hook-type puller) to remove all old packing rings from the stuffing box. Count the rings removed and record the cross-section and type. Clean the stuffing box bore and gland follower surfaces with a soft brass wire brush. Inspect the stem surface for pitting, corrosion, or scoring.

4. 4

   Size and cut new packing rings

   Measure the stuffing box bore diameter and stem diameter to calculate the packing ring cross-section. Select the correct packing grade: flexible graphite rings for temperatures above 200 degrees C or fire-safe service; PTFE for clean ambient-temperature service; braided PTFE with graphite anti-extrusion rings for fugitive emissions compliance to ISO 15848 Class A. Cut rings to length using a 45-degree bias cut (not a square cut) so the joint staggers around the stem. Pre-lubricate rings with the appropriate lubricant (valve manufacturer-specified).

   If replacing like-for-like, order pre-cut and pre-sized packing rings from the valve manufacturer for the correct stuffing box geometry. Generic rings often have incorrect dimensions.

5. 5

   Install new packing rings and compress

   Install packing rings one at a time. Stagger joints 90 degrees between adjacent rings. Install anti-extrusion (back-up) rings above and below the packing set if specified. Push each ring firmly to the bottom of the stuffing box before installing the next. Install the gland follower and hand-tighten the nuts. Operate the valve through several open/close cycles to seat the packing, then re-torque the gland nuts to the manufacturer's specification.

6. 6

   Leak test and document

   Return the valve to service pressure and check the gland area for leakage using a calibrated gas detector (EPA Method 21 for LDAR compliance) or soap bubble solution for liquid service. Re-torque if minor seeping is detected. Issue a fugitive emissions monitoring certificate if required by site LDAR programme. Document packing type, date, and next inspection interval in the valve maintenance register.

Applicable Standards

Related Products

Key Terms Explained

Unfamiliar with any terms used in this guide? Each links to a full engineering definition.