1. What Is a Trunnion Mounted Ball Valve?

A trunnion mounted ball valve is a quarter-turn valve in which the ball is supported

by trunnions (upper and lower shafts) that hold the ball firmly in position. The ball does not float

against the downstream seat as in a Floating ball valve. Instead, spring-loaded or pressure-assisted

seats move towards the ball to provide sealing.

Trunnion ball valves are typically used in:

• High-pressure pipelines
• Large diameter lines
• Oil and gas transmission and distribution
• Petrochemical and refinery units
• Pipelines requiring double block and bleed capability

Because of their robust construction, trunnion mounted ball valves provide reliable shut-off, low

torque, and long service life, but they also present specific

common problems and failure patterns that need to be understood and managed.

2. Basic Construction and Main Components

To understand common problems in trunnion mounted ball valves, it is important to

know the key components and how they interact.

2.1 Main Components

2.2 Body Construction Types

Trunnion mounted ball valves are available in different body constructions. Each body style has its

own typical problems:

3. Working Principle of Trunnion Mounted Ball Valves

A trunnion mounted ball valve is a quarter-turn valve. Turning the stem 90 degrees moves the ball

between open and closed positions. The trunnion design changes how sealing is achieved compared to

floating ball valves.

3.1 Basic Operation

• In the open position, the ball bore is aligned with the pipeline, allowing flow

  through the valve with minimal pressure drop.

• In the closed position, the ball is rotated 90 degrees so that the solid side

  of the ball faces the flow, blocking the passage.

• Trunnions at the top and bottom hold the ball in a fixed axial position.

• Seats are spring-loaded and/or pressure-energized to move against the ball to

  create sealing.

3.2 Sealing Mechanism in Trunnion Ball Valves

In trunnion mounted ball valves, the line pressure acts on the downstream seat, pushing it against

the fixed ball. This allows:

• Lower operating torque compared to floating ball valves.
• Better performance for large sizes and high pressures.
• Capability for double block and bleed design (DBB).

However, the combination of springs, seat design, and trunnion alignment introduces several

common problems such as uneven seat loading, seat sticking, excessive wear, and

inconsistent sealing.

4. Advantages and Limitations of Trunnion Mounted Ball Valves

4.1 Advantages

• Low operating torque:

  The trunnion support reduces the ball load on the seats, minimizing friction and torque.

• Suitable for large diameter and high pressure:

  The design is ideal for pipeline block valves in transmission systems.

• Double block and bleed (DBB) capability:

  Many trunnion mounted ball valves can isolate from both upstream and downstream sides and bleed

  the cavity.

• Emergency sealant injection:

  Some designs include seat and stem emergency sealant injection fittings to temporarily restore

  sealing in case of damage.

• Fire-safe options:

  Fire-safe trunnion mounted ball valves can maintain secondary metal-to-metal sealing after soft

  seals are damaged by fire.

• Versatile sealing materials:

  Soft seat (PTFE, reinforced PTFE, elastomer) or metal seat options for severe service.

4.2 Limitations and Challenges

• More complex internal design:

  Additional components (trunnions, bearings, springs) introduce more potential failure points.

• Sensitivity to contamination:

  Debris in the pipeline can damage seats, bearings, and sealing surfaces.

• Higher initial cost than some alternative valve types.

• More critical installation and alignment:

  Poor pipeline alignment or support can cause trunnion misalignment and sealing problems.

• Potential for cavity overpressure:

  If trapped fluid in the body cavity expands, overpressure can damage seals or the body.

5. Typical Specifications and Technical Data

Trunnion mounted ball valves are manufactured in a wide range of sizes, pressure classes, materials,

and end connections. The table below summarizes some typical specification ranges. Actual values

depend on standards and design.

6. Overview of Common Problems in Trunnion Mounted Ball Valves

The common problems in trunnion mounted ball valves can be grouped into several

main categories:

• Internal leakage through seats (not achieving tight shut-off)
• External leakage at stem, body joints, and end connections
• High operating torque and sticking during opening or closing
• Seat damage, erosion, extrusion, and loss of sealing capability
• Trunnion, bearing, and stem failures
• Body cavity overpressure and blocked relief paths
• Actuator and control system issues (misalignment, sizing, calibration)
• Installation, alignment, and commissioning errors
• Corrosion, erosion, and material incompatibility

The following sections examine each category in detail, including:

• Problem description
• Typical causes
• Observable symptoms
• Potential consequences
• Corrective actions and prevention strategies

7. Internal Leakage Through Seats (Seat Leakage)

Seat leakage is one of the most frequent common problems in trunnion mounted ball valves.

It refers to leakage past the closed ball through the seat area, from upstream to downstream or between

the line and the valve body cavity.

7.1 Typical Symptoms of Seat Leakage

• Downstream pressure continues to rise even when the valve is in the closed position.
• Inability to achieve specified leakage class during pressure testing.
• Unstable isolation when performing maintenance downstream of the valve.
• Unexpected flow through a supposedly isolated pipeline section.

7.2 Common Causes of Seat Leakage

7.3 Consequences of Seat Leakage

• Loss of isolation integrity and process safety hazards.
• Inability to perform safe maintenance downstream.
• Environmental releases if the leakage leads to flare or vent systems overload.
• Potential contamination between different process streams.
• Additional stress on upstream equipment due to unstable process conditions.

7.4 Troubleshooting and Corrective Actions

• Verify valve position and actuator stroke settings.
• Perform seat leakage testing in accordance with relevant standards (e.g., API 6D, ISO 5208).
• Flush the line to remove debris and contaminants before and after valve installation.
• Disassemble the valve (if design allows) to inspect seats, ball, and springs.
• Replace damaged seats and re-lap or repair ball surface if necessary.
• Check seat spring condition, material, and force; replace if fatigued or corroded.
• Confirm correct pressure direction if the valve is designed as unidirectional.

7.5 Prevention Strategies

• Install strainers, filters, or temporary screens during commissioning.
• Specify appropriate seat material for the fluid and temperature conditions.
• Ensure precise machining and finishing of ball and seat surfaces.
• Follow proper cleaning and flushing procedures before pressure testing.
• Implement periodic functional tests to detect early leakage.

8. External Leakage at Stem, Body, and End Connections

External leakage is another major category of

common problems in trunnion mounted ball valves.

It includes leakage to atmosphere from the stem packing, body joint gaskets, end connections,

and threaded plugs.

8.1 Stem Packing Leakage

The stem packing or stem seals prevent process fluid from escaping along the stem. Common stem

leakage problems include:

• Gradual leakage increase due to packing relaxation.
• Sudden leakage due to stem damage or packing extrusion.
• Leakage under thermal cycling when packing is not properly adjusted.

8.2 Body Joint and End Connection Leakage

Body joints and end connections (flanged or welded) can also be sources of leakage:

• Body-to-body or body-to-adapter gasket leakage in split or three-piece body designs.
• Flange gasket leakage due to bolt relaxation, gasket damage, or misalignment.
• Weld defects in fully welded body valves or welded end connections.

8.3 Prevention of External Leakage

• Use high-quality gaskets and packing materials compatible with process conditions.
• Control bolt torque and tightening sequence according to defined procedures.
• Perform hydrostatic shell test and seat test according to relevant standards.
• Inspect welds using appropriate non-destructive examination (NDE) methods.
• Monitor fugitive emissions, especially for valves handling hazardous or volatile fluids.

9. High Operating Torque and Stuck Ball

Abnormally high operating torque is one of the most widely reported

common problems in trunnion mounted ball valves. Excessive torque can prevent

manual operation, overload actuators, or lead to mechanical damage.

9.1 Typical Symptoms

• Difficulty turning the valve by hand even when using gear operators.
• Actuator trips due to torque overload, or fails to fully open/close the valve.
• Jerky or non-smooth motion during opening or closing.
• Sticking at intermediate positions or after being stationary for long periods.

9.2 Common Causes of High Torque

9.3 Corrective Actions and Troubleshooting

• Check actuator capability and verify that it matches specified valve torque requirements.
• Operate the valve under no-pressure conditions to compare torque with operating conditions.
• Inspect lubrication points and verify correct lubricant type and quantity.
• Check for pipeline misalignment or mechanical loads on the valve body.
• If disassembly is possible, inspect trunnions, bearings, and seats for wear or foreign objects.

9.4 Prevention of High Torque Problems

• Ensure clean pipeline conditions, particularly during commissioning.
• Specify proper clearances and surface finishes for trunnion bearings and sealing surfaces.
• Use appropriate corrosion-resistant materials for internal components.
• Perform periodic partial stroke tests for rarely operated emergency shutdown valves.
• Align the pipeline and supports correctly to prevent external loads on the valve body.

10. Seat and Sealing Surface Damage

Seat and sealing surface damage is a root cause for many other

common problems in trunnion mounted ball valves, particularly seat leakage and

high torque. Damage can occur during manufacturing, installation, or service.

10.1 Types of Seat Damage

• Abrasion and scoring from solid particles.
• Extrusion of soft seats into clearances at high pressure or temperature.
• Thermal cracking or deformation in high-temperature services.
• Chemical attack leading to swelling, shrinking, or embrittlement.
• Mechanical impact damage from improper handling or assembly.

10.2 Damage to Ball and Metal Sealing Surfaces

Metal-to-metal sealing systems (e.g., metal seats with hard-faced balls) are used in severe

conditions such as high temperature, slurry service, or erosive media. Typical problems include:

• Loss of hard coating due to poor adhesion or improper application.
• Erosion of hard surfaces in high-velocity abrasive flows.
• Galling and seizure between ball and seat in poorly lubricated or incompatible materials.

10.3 Strategies to Minimize Seat and Surface Damage

• Use upstream filtration and strainers to remove solid particles.
• Select suitable seating materials and coatings for the specific service conditions.
• Define controlled opening and closing speeds to minimize erosion from throttling.
• Avoid using isolation valves for throttling when not specifically designed for it.
• Implement proper handling and storage procedures to avoid mechanical damage before installation.

11. Trunnion and Bearing Failures

Trunnion and bearing issues are critical common problems in trunnion mounted ball valves.

They directly influence valve operability, torque, and alignment.

11.1 Typical Failure Modes

• Wear of trunnion journals and bearings.
• Corrosion of trunnion and bearing surfaces.
• Seizure of trunnion bearings due to contamination or inadequate lubrication.
• Bending or fracture of trunnion due to excessive loads or misalignment.

11.2 Causes and Contributing Factors

11.3 Inspection and Maintenance of Trunnions and Bearings

• Monitor operating torque trend; an increasing trend may indicate bearing problems.
• During overhaul, inspect trunnion surfaces for scoring or corrosion.
• Check bearing clearances and replace worn or seized bearings.
• Ensure correct assembly orientation and alignment of trunnion components.

12. Body Cavity Overpressure and Blockage

Body cavity overpressure is a critical safety-related

common problem in trunnion mounted ball valves.

The closed valve can trap fluid in the cavity between the seats and the ball. If this trapped fluid

expands due to temperature changes, the pressure in the cavity can increase dramatically.

12.1 Causes of Cavity Overpressure

• Thermal expansion of trapped liquid in the cavity.
• Gas expansion due to temperature increase or external fire exposure.
• Blockage of cavity relief paths by solid particles or malfunctioning devices.

12.2 Consequences of Overpressure

• Seat damage or extrusion, leading to internal or external leakage.
• Distortion or rupture of the valve body in extreme cases.
• Uncontrolled release of process fluid with safety and environmental consequences.

12.3 Cavity Relief Design Features

To prevent overpressure, trunnion mounted ball valves typically have cavity relief measures such as:

• Automatic relief to upstream side via seat design.
• Automatic relief to downstream side where appropriate.
• Dedicated cavity relief valves or connections.

12.4 Common Problems with Cavity Relief

• Improper orientation or installation disabling relief function.
• Seat design not providing sufficient relief capacity.
• Blockage or plugging of relief paths by deposits or debris.

12.5 Recommended Practices

• Confirm cavity relief design according to standards and application.
• Periodically verify body cavity relief functionality.
• Avoid trapped liquid conditions where possible or control temperature changes.

13. Actuator and Control Problems

Many common problems in trunnion mounted ball valves are related to actuators

and control systems rather than the valve body itself. Actuators must deliver adequate torque,

speed, and control accuracy for the valve to perform properly.

13.1 Typical Actuator-Related Problems

• Undersized actuator unable to overcome required torque.
• Incorrect air or hydraulic supply pressure for pneumatic or hydraulic actuators.
• Misadjusted limit switches or positioners leading to partial opening/closing.
• Excessive operating speed causing water hammer or mechanical shock.
• Actuator mounting misalignment causing side loads on stem.

13.2 Manifestations in Valve Performance

• Valve fails to reach full closed or open position.
• Seat leakage due to incomplete closure.
• Vibration or oscillation during operation.
• Inconsistent response time in emergency shutdown scenarios.

13.3 Corrective and Preventive Actions

• Perform actuator sizing calculations with appropriate safety factors.
• Verify supply pressure and capacity for pneumatic or hydraulic actuators.
• Align actuator with valve stem according to mounting guidelines.
• Adjust travel stops and limit switches to ensure correct end positions.
• Implement periodic functional tests, including stroke time measurement.

14. Installation and Commissioning Issues

Many common problems in trunnion mounted ball valves can be traced back to

improper installation and commissioning practices. Even a well-designed valve can fail prematurely

if not installed correctly.

14.1 Installation-Related Problems

• Pipeline misalignment causing mechanical stress on the valve body and trunnions.
• Insufficient support for heavy valves leading to sagging and misalignment.
• Welding spatter and debris left inside the valve after in-line welding.
• Improper torqueing of flange bolts or body bolts affecting gasket compression.
• Wrong orientation of valve in relation to flow direction or gravity.

14.2 Commissioning-Related Problems

• Failure to flush and clean pipelines before first operation.
• Rapid pressurization causing shock loads on seats and internals.
• Insufficient pre-lubrication of trunnion bearings and stem seals.
• Skipping functional stroke testing before putting the valve into service.

14.3 Good Practices for Installation and Commissioning

• Verify alignment of flanges and pipes before tightening bolts.
• Provide structural supports for large and heavy trunnion mounted ball valves.
• Use proper gasket type and bolt torquing sequence.
• Thoroughly clean and flush the pipeline to remove debris and welding slag.
• Conduct hydrostatic tests and functional stroke tests as per applicable standards.

15. Operation and Maintenance Recommendations

Proper operation and maintenance practices greatly reduce the frequency and severity of

common problems in trunnion mounted ball valves.

15.1 Basic Operating Guidelines

• Operate the valve only within its designed pressure and temperature limits.
• Avoid using on-off valves for throttling unless specifically designed for control service.
• Open and close the valve at recommended speeds to prevent pressure surges.
• Regularly operate rarely used valves to prevent sticking and deposits build-up.

15.2 Preventive Maintenance Activities

15.3 Condition Monitoring

To anticipate problems before failure, many operators use condition monitoring techniques such as:

• Trend monitoring of operating torque and actuator pressure.
• Acoustic emission or vibration monitoring during operation.
• Leakage rate measurement using flow meters or pressure decay tests.
• Fugitive emission monitoring around stem and body joints.

16. Inspection, Testing, and Relevant Standards

Proper inspection and testing practices are essential for identifying and preventing

common problems in trunnion mounted ball valves. Several standards define

design, manufacturing, and testing requirements.

16.1 Common Design and Manufacturing Standards

• API 6D – Specification for Pipeline Valves
• API 608 – Metal Ball Valves, Flanged, Threaded and Welding Ends
• ISO 14313 – Petroleum and natural gas industries — Pipeline transportation systems — Pipeline valves
• ASME B16.34 – Valves – Flanged, Threaded, and Welding End

16.2 Testing Standards and Methods

• Hydrostatic shell tests to verify body strength and tightness.
• Seat leakage tests at rated pressure and low pressure.
• Fire-safe tests in accordance with fire-safe standards (e.g., API 607, ISO 10497).
• Fugitive emission tests for environmental compliance.

16.3 Typical Inspection Checklist

17. Materials and Corrosion Considerations

Incorrect material selection is a fundamental cause of several

common problems in trunnion mounted ball valves, especially corrosion,

erosion, and stress-related failures.

17.1 Typical Corrosion Problems

• General corrosion reducing wall thickness of body and end connections.
• Pitting and crevice corrosion on balls and seats in chloride-containing environments.
• Sulfide stress cracking and hydrogen-induced cracking in sour service.
• Galvanic corrosion between dissimilar metals.

17.2 Erosion and Erosion-Corrosion

High-velocity flow with suspended solids can cause:

• Erosion of seat sealing surfaces.
• Thinning in localized areas of the body or ball.
• Accelerated damage where corrosion and erosion act together.

17.3 Material Selection Guidelines

• Select body and trim materials compatible with fluid composition and temperature.
• Use proper hardness and coatings on ball and seats to resist wear.
• Consider corrosion allowance and protective coatings for external surfaces.
• For sour service, comply with NACE or equivalent requirements for crack resistance.

18. Best Practices for Long-Term Reliability

Achieving long-term reliable performance and minimizing

common problems in trunnion mounted ball valves requires a holistic approach

covering selection, design, installation, operation, and maintenance.

18.1 Selection and Design Stage

• Define operating conditions accurately (pressure, temperature, fluid, solids, cycling frequency).
• Select appropriate design standard and pressure class for the application.
• Specify seat material, body material, coatings, and fire-safe requirements correctly.
• Ensure adequate margin in actuator sizing for worst-case torque.

18.2 Procurement and Manufacturing Stage

• Require documented quality control and material traceability.
• Review test procedures and witness critical tests when appropriate.
• Ensure cleanliness requirements for internal surfaces and cavities.

18.3 Field Installation and Commissioning

• Use proper lifting and handling techniques for heavy trunnion mounted ball valves.
• Align pipeline and supports to avoid undue stress on valves.
• Flush and clean lines thoroughly before putting valves into operation.
• Perform functional tests including open/close strokes and leakage checks.

18.4 Operation and Maintenance

• Follow operating procedures, avoiding overpressure and overheating.
• Execute preventive maintenance plans, including periodic inspections and lubrication.
• Monitor performance indicators such as torque, leakage, and response time.

18.5 Failure Analysis and Continuous Improvement

When failures or significant problems occur, conduct systematic root cause analysis to identify

and correct underlying issues. Sharing lessons learned across similar installations can prevent

repeat events and improve overall reliability.

19. FAQ: Common Questions About Trunnion Mounted Ball Valve Problems

Q1. Why do trunnion mounted ball valves often have lower torque than floating ball valves?

In trunnion mounted ball valves, the ball is supported by trunnions, so line pressure acts mainly on

the seats rather than on the ball. The seats move towards the ball, reducing the seat load on the ball

and thereby decreasing friction and required torque. This is a major reason why trunnion mounted ball

valves are preferred for large sizes and high pressure services.

Q2. What is the most common problem in trunnion mounted ball valves?

While the exact ranking varies, some of the most common problems include:

• Seat leakage due to damage or wear.
• Stem packing leakage (external leakage).
• High operating torque caused by contamination or inadequate lubrication.
• Installation-related issues like misalignment and debris in the line.

Q3. How can I detect early-stage problems in trunnion mounted ball valves?

Effective methods for early detection include:

• Monitoring torque trends during operation.
• Visual inspection for leaks at stem, body, and end connections.
• Checking valve stroke time and completeness of opening/closing.
• Periodic leak tests for critical isolation valves.

Q4. Are trunnion mounted ball valves suitable for throttling service?

Standard trunnion mounted ball valves are primarily designed as on-off isolation valves. Continuous

throttling can cause erosion, cavitation damage, and seat wear, increasing the risk of leakage and

other problems. For control applications, valves specifically designed for throttling (such as control

ball valves or globe valves) are usually preferred.

Q5. What causes body cavity overpressure in trunnion mounted ball valves?

Body cavity overpressure occurs when fluid trapped between closed seats and the ball expands due to

temperature changes, especially for incompressible liquids. Without adequate cavity relief design or

if relief paths are blocked, this can lead to high stresses, seat damage, and possible body failure.

Q6. How often should trunnion mounted ball valves be overhauled?

Overhaul intervals depend on service severity, operating frequency, and criticality. In many pipeline

applications, major internal inspection and overhaul may be performed every 5–10 years, while more

severe or critical services may require shorter intervals. Condition monitoring can help optimize

these intervals.