1. Introduction to Fixed Ball Valves

Fixed ball valves are quarter-turn shut-off valves designed to provide reliable isolation in high-pressure,

large-diameter, and demanding service conditions. Unlike floating ball valves, where the ball is held in

place by the seats, a fixed ball valve uses a trunnion or shaft support at the top and bottom of the ball.

This design significantly reduces operating torque and seat wear, making fixed ball valves suitable for

critical applications in oil and gas, petrochemical, power generation, and general industrial service.

International standards from bodies such as the American Petroleum Institute (API) and the International

Organization for Standardization (ISO) define the design rules, dimensions, materials, testing methods, and

documentation requirements for fixed ball valves. Understanding these standards helps engineering,

procurement, and maintenance teams specify, compare, and qualify valves for safe and reliable operation.

2. What Is a Fixed (Trunnion-Mounted) Ball Valve?

A fixed ball valve, commonly called a trunnion-mounted ball valve, is a ball valve in which the ball is

mechanically supported by shafts or trunnions at two points. The ball does not float downstream under

pressure; instead, the seat rings are energized to move toward the ball and create a tight seal.

2.1 Key Characteristics

• Ball is supported by upper and lower trunnions or shafts.
• Seat rings are spring-loaded or pressure-energized.
• Lower operating torque compared to Floating ball valves.
• Suitable for high-pressure and large-diameter pipelines.
• Available in soft-seated and metal-seated configurations.
• Commonly designed to API and ISO ball valve standards.

2.2 Typical Applications

• Transmission pipelines for crude oil and natural gas.
• Refinery and petrochemical process units.
• Offshore and subsea production systems.
• Power generation (steam, gas, and combined cycle plants).
• Industrial utility services where tight shutoff is required.

3. Advantages of Fixed Ball Valves

Fixed ball valves are widely specified due to their performance, reliability, and operational benefits. The

advantages become especially important in high-pressure and large-bore services where maintenance and

downtime are costly.

3.1 Operational Advantages

• Reduced Operating Torque:

  The trunnion support eliminates the need for the ball to move against the seats under pressure, which

  lowers torque and allows smaller actuators or easier manual operation.

• Consistent Seal Performance:

  Spring-energized or pressure-energized seats maintain a reliable seal over a wide range of pressures and

  temperatures.

• Bidirectional Sealing:

  Many fixed ball valves, designed according to API and ISO standards, provide tight shutoff in both flow

  directions.

• Long Service Life:

  Reduced seat wear and optimized load distribution around the ball contribute to extended valve service

  intervals.

3.2 Safety and Environmental Advantages

• Low Fugitive Emissions:

  Compliance with emission standards such as ISO 15848 parts 1 and 2 or API 641 helps reduce leakage from

  stems and body joints, supporting environmental and safety goals.

• Fire-Safe Design:

  Many fixed ball valves are tested to API 607, ISO 10497, or similar fire-safe standards, ensuring

  sealing integrity during and after fire exposure.

• Double Block and Bleed (DBB):

  Trunnion-mounted ball valves are often used in DBB configurations, allowing pipeline isolation and

  cavity venting for maintenance and safety checks.

3.3 Economic and Maintenance Advantages

• Lower Actuation Costs:

  Lower torque requirements minimize actuator size and energy consumption for automated systems.

• Reduced Downtime:

  Robust design and standardized parts lead to fewer unplanned shutdowns and easier maintenance planning.

• Standardization Benefits:

  Conformance to recognized API and ISO standards simplifies qualification, inspection, and global

  procurement.

4. Overview of API and ISO Standards for Fixed Ball Valves

Fixed ball valves are governed by multiple overlapping and complementary standards. The most widely

referenced are produced by API and ISO, which cover design, dimensions, testing, fire safety, and fugitive

emissions. Selecting a valve that complies with these standards ensures compatibility, safety, and

consistent performance.

4.1 Major API Standards Relevant to Fixed Ball Valves

4.2 Major ISO Standards Relevant to Fixed Ball Valves

In many projects, a fixed ball valve may be designed according to both API 6D and ISO 14313, or according

to ISO 17292 with supplementary API requirements. Understanding the hierarchy and cross-references between

these standards is essential for accurate specification.

5. Design Features of Fixed Ball Valves under API and ISO Standards

API and ISO standards define critical design aspects of fixed ball valves to ensure safety, functionality,

and interchangeability. Although the detailed calculations and formulas are contained within the

standards, the following highlights the most important design features governed by these documents.

5.1 Pressure and Temperature Ratings

Fixed ball valves are assigned pressure–temperature ratings based on material groups and end-connection

standards. Typical references include ASME B16.34 for steel valves and ASME B16.5 or B16.47 for flanges. API

6D and ISO 14313 incorporate these ratings for pipeline valves.

5.2 Body Construction Types

Fixed ball valves are available in several body constructions, all of which must meet the strength and

leak-tightness requirements specified in API 6D, API 608, and ISO 17292.

• One-piece Body: Compact, generally limited to smaller sizes and lower pressures.
• Two-piece Split Body: Widely used for pipeline and process service, balancing

  manufacturability and maintenance access.

• Three-piece Body: Facilitates inline maintenance; more common in smaller sizes and

  lower pressure classes.

• Top-entry Design: Allows access to internal components from the top; often used in

  high-pressure or high-integrity applications where inline overhaul is necessary.

5.3 Seat Design and Cavity Relief

In trunnion-mounted ball valves, the seat rings are typically spring-loaded and pressure-energized. API 6D

and ISO 17292 require that valves be designed to prevent overpressure in the body cavity, often achieved

through:

• Self-relieving seats that allow overpressure in the cavity to push the seat away from the ball.
• Dedicated cavity relief valves that vent pressure to a safe location.
• Compliance with double block and bleed or double isolation and bleed configurations where specified.

5.4 Stem and Anti-Blowout Features

API and ISO ball valve standards mandate that the valve stem be designed to prevent blowout under pressure.

This is usually accomplished by:

• Inserting the stem from inside the valve body.
• Using retainer rings or collars under the packing area.
• Ensuring sufficient stem-to-ball engagement to transmit torque safely.

Additional stem design features may include live-loaded packing and stem extension options for low

temperature or underground installations.

6. Materials for Fixed Ball Valves in API and ISO Standards

Material selection is fundamental to safe and long-lasting performance. API and ISO standards specify

permissible body, ball, stem, and trim materials, along with heat treatment and impact testing requirements.

6.1 Common Body and Bonnet Materials

6.2 Ball, Stem, and Trim Materials

The ball and stem materials are selected to balance strength, corrosion resistance, and galling resistance.

Hard-facing or overlay materials may be applied to seating surfaces for severe service.

• Ball: Typically stainless steel or alloy steel; may be hard-coated (e.g., chromium

  carbide, tungsten carbide) for erosive or high-cycle applications.

• Stem: High-strength stainless or alloy steel; surface treatments can improve wear and

  corrosion resistance.

• Seats: Soft seats (PTFE, reinforced PTFE, PEEK) or metal seats with hard-facing for

  high-temperature or abrasive service.

6.3 Sealing and Packing Materials

Seat and packing materials significantly influence valve performance, especially regarding emissions,

fire-safety, and temperature resistance. Common materials include:

• PTFE and filled PTFE for general-purpose, low-friction soft seats.
• PEEK for higher temperature and improved chemical resistance.
• Elastomers (e.g., NBR, FKM) for O-rings, depending on media compatibility.
• Graphite packing and gaskets for fire-safe designs and high-temperature applications.

7. Dimensional and End Connection Requirements

API and ISO fixed ball valve standards define critical dimensions to ensure compatibility with piping

systems. These include face-to-face dimensions, end connection types, and bore configurations.

7.1 Face-to-Face Dimensions

Face-to-face (or end-to-end) dimensions are generally standardized according to ISO 5752, ASME B16.10, or

related dimensional standards referenced by API 6D and ISO 17292. This allows interchangeability between

valves from different manufacturers as long as they comply with the same standard.

7.2 End Connection Types

7.3 Bore Configurations

• Full Bore (Full Port): The flow passage matches the pipe diameter, minimizing pressure

  drop and allowing pigging in pipeline systems.

• Reduced Bore (Reduced Port): The flow passage is smaller than the pipe diameter, which

  may be acceptable in process applications where slight pressure drop is not critical.

API 6D and ISO 14313 specify bore sizes suitable for piggable pipeline valves, making full-bore fixed ball

valves the standard choice for many transmission systems.

8. Testing and Inspection Requirements

Testing is central to both API and ISO standards for fixed ball valves. These tests verify that valves meet

the required integrity, tightness, and performance criteria before installation in the field.

8.1 Hydrostatic and Pneumatic Testing

Hydrostatic shell and seat tests are required by API 6D, API 598, ISO 5208, and ISO 17292. Typical tests

include:

• Shell Strength Test: The body is subjected to a specified test pressure (usually

  higher than design pressure) with the valve partially open to check for body and bonnet leakage.

• Seat Leakage Test: With the valve fully closed, pressure is applied from each side to

  assess seat sealing performance and establish leakage class.

ISO 5208 and API 598 classify allowable leakage rates. For many critical applications, fixed ball valves

must meet very tight leakage limits (such as zero visible leakage).

8.2 Functional Testing

In addition to pressure testing, API and ISO standards may require:

• Operational testing across the full stroke to confirm torque, smoothness, and correct orientation.
• Verification of position indicators and any locking devices.
• Testing of actuator–valve assemblies where supplied as a complete unit.

8.3 Fire Testing

Fire-safe certification is commonly mandated in hydrocarbon service. Fire testing according to API 607,

API 6FA, or ISO 10497 verifies that a fixed ball valve can maintain acceptable leakage levels when exposed

to fire and subsequent cooling.

• Nonmetallic seat and sealing materials are tested for fire resistance.
• Valve integrity under elevated temperature and thermal shock is confirmed.
• Post-fire operability and leakage performance are assessed.

8.4 Fugitive Emissions Testing

To address environmental regulations, many fixed ball valves are type-tested to fugitive emission

standards:

• ISO 15848-1 and ISO 15848-2 set test sequences and leakage limits for stem and body joints.
• API 641 provides a specific low-emission test protocol, focusing on methane or hydrocarbon leaks.

Meeting these standards ensures that fixed ball valves contribute to reduced emissions and regulatory

compliance.

9. Fixed Ball Valve Selection Criteria Based on API and ISO Standards

Selecting a fixed ball valve for a given application involves more than choosing a size and pressure class.

API and ISO standards provide guidance that can be translated into practical selection criteria.

9.1 Basic Sizing Parameters

9.2 Functional and Safety Requirements

• Determine whether double block and bleed or double isolation and bleed

  is required.

• Check if fire-safe certification according to API 607 or ISO 10497 is mandatory.
• Assess fugitive emissions limits and specify ISO 15848 or API 641 testing where

  needed.

• Identify need for emergency sealant injection systems on seats and stem.
• Confirm compatibility with actuation (manual, gear, pneumatic, hydraulic, or electric

  actuators).

9.3 Environmental and Installation Conditions

• For buried or underground valves, ensure suitable coatings, extended stems, and actuator arrangements.
• For offshore environments, consider corrosion resistance and protective coatings as guided by offshore

  design standards.

• For cryogenic or very low temperatures, evaluate compliance with low-temperature testing and materials

  requirements.

10. Comparison: Fixed vs. Floating Ball Valves under API and ISO

Understanding the difference between fixed (trunnion-mounted) and floating ball valves helps in correct

standard-based selection.

In standardized specifications, the choice between fixed and floating ball valves depends on pressure,

diameter, and service criticality. API and ISO standards allow both types but emphasize trunnion-mounted

designs for high-integrity pipeline applications.

11. Sample Specification Table for Fixed Ball Valves (API / ISO Based)

The following example shows how key parameters for fixed ball valves can be presented in a specification

table for project or catalog use. Values are illustrative and must be confirmed against specific project

requirements and applicable standards.

12. Documentation and Compliance for Fixed Ball Valves

API and ISO standards not only address the physical design of fixed ball valves but also define

documentation and quality assurance requirements. These help ensure traceability and compliance throughout

a valve’s lifecycle.

12.1 Typical Documentation Package

• Material test certificates complying with EN 10204 or equivalent (e.g., 3.1 or 3.2).
• Pressure test reports per API 6D, API 598, or ISO 5208.
• Fire test and fugitive emissions certificates where applicable.
• Dimensional inspection records and non-destructive examination reports.
• Assembly drawings, parts lists, and operating manuals.

12.2 Quality and Manufacturing Standards

Many end-users require that manufacturers of fixed ball valves operate quality management systems certified

to ISO 9001. Additional certifications, such as ISO 14001 (environmental) and ISO 45001 (occupational

health and safety), may also be considered in project specifications.

13. Frequently Asked Questions about Fixed Ball Valve Standards

13.1 Are fixed ball valves always designed to API 6D?

Fixed ball valves used in transmission pipelines are usually designed to API 6D or its international

equivalent ISO 14313. However, trunnion-mounted valves for refinery, petrochemical, or general industrial

service may instead follow API 608 and ISO 17292. The appropriate standard depends on the application and

project specification.

13.2 Do all fixed ball valves require fire-safe certification?

Fire-safe certification is typically required in hydrocarbon and hazardous service. For benign media such

as water or non-flammable fluids, fire-safe testing may not be mandatory. Project specifications determine

whether compliance with API 607, API 6FA, or ISO 10497 is required.

13.3 How do API and ISO standards address fugitive emissions?

Fugitive emissions requirements are defined mainly by ISO 15848-1/2 and API 641. These standards set test

conditions, number of operating cycles, and leakage limits. Many fixed ball valves are designed with

advanced stem packing systems and body seals to meet these criteria.

13.4 Is a full-bore fixed ball valve always needed for pipelines?

Full-bore fixed ball valves are preferred for piggable pipelines so that inspection and cleaning devices

can pass through. In non-piggable systems or process lines, reduced-bore designs may be acceptable if

pressure drop and flow characteristics remain within design limits.

14. Conclusion

Fixed (trunnion-mounted) ball valves play a central role in modern pipeline and process systems. API and ISO

standards provide a comprehensive framework for the design, manufacturing, testing, and qualification of

these valves. By specifying valves that comply with established standards such as API 6D, API 608, ISO

17292, and ISO 14313, engineering and procurement teams can ensure high levels of safety, reliability, and

regulatory compliance.

When evaluating or specifying fixed ball valves, it is advisable to consider not only size and pressure

rating but also materials, end connections, sealing technology, fire-safety requirements, and fugitive

emission performance. Leveraging API and ISO requirements as a common reference point simplifies

comparison, improves system compatibility, and supports long-term operational efficiency.