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Valve Leakage Classification and On-Site Troubleshooting
Created on 08.31
Valve Leakage Classification and On-Site Troubleshooting – A Practical Guide
Valve leakage can be categorised into several types: packing leakage, flange leakage, body leakage, and internal leakage (seat leakage). Each type has its own root causes and corresponding field remedies. The following summary is compiled based on actual operating experience.
1. Packing Leakage – The Most Frequent Leakage Location
Root Causes
Packing leakage occurs because, during valve operation, the stem rotates (as in ball valves, butterfly valves, etc.) or moves axially (as in control valves, gate valves, globe valves, etc.), causing the packing to wear, age, and lose its sealing force. The pressurised medium then escapes along the clearance between the packing and the stem. Over time, the escaping medium may blow out portions of the packing and erode grooves on the stem surface, further aggravating the leakage.
On-Site Remedies
- In most cases,
tightening the gland or replacing the packing can resolve the problem.
- If the packing box wall thickness is approximately 8 mm or greater,
injection-type online leak sealing can be applied – i.e., drilling and tapping a hole in the packing box outer wall and injecting a sealing compound under pressure to stop the leak.
2. Flange Leakage – Common Failure at Connection Joints
Root Causes
Flange sealing relies on the bolt preload to create sufficient specific sealing pressure on the gasket. Leakage may result from:
- Insufficient gasket compression force
- Poor surface finish of the flange facing (roughness not meeting requirements)
- Gasket deformation or relaxation
- Mechanical vibration
- Bolt deformation or elongation
- Gasket ageing, loss of resilience, or cracking
On-Site Remedies
- Re-torque the flange bolts evenly to the specified preload.
- If the gasket is damaged, it must be replaced (requires depressurisation and shutdown).
- In some cases, temporary sealant injection may be attempted, but this is less common for flange leaks.
3. Internal Leakage (Seat Leakage) – Consequence of Incomplete Shut-Off
Root Causes
Internal leakage can have multiple causes:
- Sealing surfaces not lapped flat or smooth enough
- Poor fit between the seat and the sealing ring
- Loose connection between the disc (or plug) and the stem
- Stem bent or twisted, causing misalignment of the closure member
- Excessive closing speed causing impact damage
- Improper material selection, leading to corrosion damage
In addition, using a gate valve or globe valve as a throttling (control) device can also lead to internal leakage due to seat erosion.
On-Site Remedies
- First, secure the seat retaining plate (or body seat ring) and increase bolt preload to promote plastic deformation of the sealing ring and reduce clearance.
- For minor internal leakage, sealing compound can be injected through the grease/sealant injection port to temporarily restore tightness.
- If the seat or disc is severely damaged, the valve must be taken out of service for grinding or replacement of sealing elements.
4. Body Leakage (External from Casting Defects)
Root Causes
Cast valve bodies may contain inherent defects such as:
- Porosity (gas holes)
- Slag inclusions
- Cracks
- Sand holes or shrinkage cavities
If these casting defects are not detected during factory inspection or are inadequately repaired, they may become apparent during field service and result in external leakage through the body wall.
On-Site Remedies
- Minor pinhole leaks may be temporarily stopped by peening or by applying a sealant patch.
- Permanent repair typically requires
weld repair (after proper preparation and with qualified welding procedures), followed by post-weld heat treatment and NDE.
- If the defect is extensive, the valve body must be replaced.
5. Control Valve Malfunctions – Jamming/Clogging and Oscillation
5.1 Jamming / Clogging
Root Cause:
In newly commissioned systems or systems after major overhaul, weld spatter, scale, iron filings, and other debris tend to accumulate at the throttling orifice and guiding surfaces, causing the control valve to jam.
On-Site Remedy:
- Flush the upstream piping thoroughly before commissioning.
- If jamming occurs, disassemble the valve and clean the trim and guide surfaces.
- Install a strainer or filter upstream of the control valve to prevent ingress of solid particles.
5.2 Oscillation (Hunting)
Root Cause:
Control valve oscillation is often related to:
- Inadequate spring stiffness (spring rate too low)
- Improper valve sizing (oversized or undersized)
- Incorrect actuator selection
- Excessive friction in packing or guiding surfaces
On-Site Remedy:
- Check and adjust the actuator bench set or spring range.
- Verify valve sizing against process conditions; if the valve is oversized, consider trim reduction or replacement.
- Ensure the packing friction is within acceptable limits by proper lubrication or packing adjustment.
- In severe cases, re-evaluate the control valve selection and replace with a properly sized unit.
Summary of On-Site Leakage Troubleshooting
Leakage Type | Primary Causes | Quick Field Action |
Packing | Stem wear, packing ageing | Tighten gland or replace packing; inject sealant (if wall thickness permits) |
Flange | Loose bolts, gasket failure | Re-torque bolts; replace gasket if necessary |
Internal (seat) | Worn sealing surfaces, misalignment | Increase seat preload; inject sealing compound; later grind or replace seat/disc |
Body (external) | Casting defects (pores, cracks) | Temporary seal; permanent weld repair or replace body |
Control valve jamming | Debris in flow path | Clean valve and trim; install upstream strainer |
Control valve oscillation | Spring stiffness mismatch, oversizing | Adjust spring setting; re-size valve; reduce actuator friction |
This guide is intended for maintenance engineers and field technicians working with industrial valves in petrochemical, power, and process plant environments.
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