Globe ValvesModerate4–8 hours5 steps

Globe Valve Seat Leakage / Wire-Drawing Erosion

Globe valve seat leakage is typically caused by wire-drawing erosion - a high-velocity groove eroded through the seat face when the valve is operated at a partial opening for extended periods. This is the most common failure mode for globe valves in throttling service.

Symptoms

Increasing leakage past the closed valve over months of serviceVisible groove or channel across the seating face on inspectionIncreased noise (hissing) through a closed valveFlow continues slowly downstream even with valve fully closed and full stem torque applied

Root Causes

1

Wire-drawing erosion

High-velocity flow through the narrow gap between the disc and seat at partial opening creates a focused erosion path. Over time, this erodes a groove (wire-draw) through the seat face that provides a bypass path even when the valve is fully closed.

2

Incorrect throttling range

A globe valve should be sized so it operates between 20–80% open for the required flow range. Valves throttling very close to the seat (less than 10% open) create extreme velocity and erosion.

3

Seat material incompatibility

Soft seat inserts (PTFE, PEEK) attacked by the process fluid at the operating temperature swell, crack, and fail to seal.

4

Particulate erosion

Solid particles in the flow stream (catalyst fines, scale, sand) abrade the seat and disc face as they accelerate through the valve restriction.

Safety Precautions

  • Full LOTO and cooldown before disassembly
  • Steam and hot fluid lines: allow to reach below 60 degrees C before opening bonnet

Tools Required

  • Valve seat ring removal wrench (manufacturer-specific)
  • Lapping plate and compound
  • Torque wrench
  • Blue engineers' marking compound
  • Heat torch or heating blanket (for seat ring removal)

Supplies Needed

  • Replacement seat ring (correct material)
  • Replacement disc/plug
  • Lapping compound (100 and 200 mesh)
  • Thread sealant for seat ring installation

Step-by-Step Repair Guide

  1. 1

    Identify the seat material and damage extent

    Isolate, depressurise, and open the globe valve fully. Use a torch to inspect the seat ring face from above (with bonnet/disc removed). Wire-draw damage appears as a distinct groove or channel across the annular seating face, usually at one point on the circumference. Mild damage (groove less than 0.5 mm deep): lapping is possible. Severe damage (groove more than 0.5 mm deep, or encircling more than 60 degrees of the seat circumference): seat ring replacement required.

  2. 2

    Lapping procedure for mild wire-draw

    Apply valve lapping compound to the disc face. Place the disc on the seat. Using the stem, rotate the disc back and forth over a 30-degree arc while applying moderate downward force, working the compound into the damage. Periodically clean and apply fresh compound. Check progress with blue engineers' marking compound applied to the disc - a continuous, even ring indicates full contact. A typical light wire-draw lapping job takes 30–90 minutes.

    Grade 100 mesh compound for initial cutting; then Grade 200 for finishing. Never use coarser than 80 mesh on valve seats.

  3. 3

    Seat ring replacement for severe damage

    On globe valves with replaceable seat rings: heat the body around the seat ring area (to 150–200 degrees C) to expand the body, then use a seat ring removal wrench (matching the seat ring's notches) to unscrew the ring. Clean the seat ring threads in the body. Apply Loctite 577 or similar thread sealant to the new seat ring threads, install, and torque to the manufacturer's specification. For integral (non-replaceable) seats, weld repair by a specialist is required.

  4. 4

    Replace disc/plug if damaged

    Inspect the disc face for corresponding wire-draw damage. If the disc shows a matching groove, it must also be refaced or replaced - a lapped seat on a damaged disc will re-erode rapidly. Disc replacement is typically a simpler task than seat ring replacement.

  5. 5

    Verify Cv and resize if throttling range was too close to closed

    If wire-draw is a recurring issue, the valve is likely oversized for the required flow. A valve throttling below 20% open continuously will wire-draw rapidly. Review the Cv calculation and replace with a valve 1–2 sizes smaller, or specify a characterized disc profile (equal-percentage characteristic) that gives better control at low openings.

When to Replace Instead of Repair

Replace the complete valve if seat ring is integral and damage exceeds lapping depth, or if the valve is persistently oversized and requires replacement with a correctly sized model.

Key Terms Explained

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

Globe ValveSeatThrottlingTrim
Full valve glossary (113 terms)
For reference only. These guides are general engineering information intended to help maintenance teams understand common valve fault patterns. They do not replace site-specific procedures, manufacturer service instructions, or applicable codes and standards (ASME, API, IEC). Always work under a valid Permit-to-Work (PTW) with Lock-Out Tag-Out (LOTO) applied. Consult a qualified engineer before undertaking any maintenance on safety-critical, high-pressure, or hazardous-fluid systems. Vajra Industrial Solutions accepts no liability for actions taken based on this content.

Quick Reference

Difficulty
Moderate
Est. Time
4–8 hours
Steps
5
Category
Globe Valves
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Steps

  1. 1Identify the seat material and damage extent
  2. 2Lapping procedure for mild wire-draw
  3. 3Seat ring replacement for severe damage
  4. 4Replace disc/plug if damaged
  5. 5Verify Cv and resize if throttling range was too close to closed

Key Terms

Full glossary (113 terms) →

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