Ball Valves For High-Pressure Applications
Figure 1: High-pressure ball valve
High-pressure ball valves provide a reliable and efficient shut-off in high-pressure applications. These valves are designed with unique features such as durable materials, robust construction, and tight sealing to ensure reliable operation under high pressure. This article discusses the main features and selection criteria of high-pressure ball valves. Read our ball valve overview article for more information on the construction, working, and types of ball valves.
Table of contents
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High-pressure ball valves
As the name suggests, a high-pressure ball valve works under high fluid pressure, approximately 500 - 700 bars (7252 - 10152 psi). These ball valves are used in applications where large volumes of fluid are stored and precise flow control is required, like, water distribution plants, chemical industries, and water parks. These valves are specially designed to withstand continuous use under these severe conditions. Ball valves are widely used in high-pressure applications due to their unique features.
- Ball valves provide leak proof sealing or a bubble-tight closure, preventing any pressure drops that may occur in the event of a leakage.
- Full-port ball valves do not interfere with the flow when open, thereby providing minimal pressure loss.
- The structure of the ball enables the valve to be opened in high-pressure systems, provided that the actuator is correctly sized. The ball's shape also allows it to move smoothly across the high-pressure flow, which helps the valve operate effectively.
- High-pressure piping systems are prone to water hammer. However, ball valves are useful in minimizing them.
Design features
- Decreased port size: The valve's pressure rating increases when the valve size decreases. For example, a larger ball valve with a diameter of 6 inches may be rated for a pressure of 41 bar (600 psi), while a smaller ball valve with a diameter of 2 inches may be rated for a pressure of 103 bar (1500 psi) because the higher velocity of the fluid flowing through the smaller valve requires a higher pressure rating to maintain the desired downstream pressure.
- Heavy-duty materials: High pressure ball valves are made of high-quality materials that withstand extreme pressures and temperatures. Common materials include stainless steel, titanium, and other corrosion-resistant alloys.
- Reinforced seats and seals: The valve seats and seals in high-pressure ball valves are reinforced with materials such as PTFE, graphite, or metal to withstand high pressures and temperatures without leaking. Read our chemical resistance guide to know more about the compatibility of different materials to various media and their working temperature range.
- Full-bore design: High pressure ball valves are typically designed with a full bore, which means the internal diameter of the valve is the same as the pipe it is connected to. This reduces flow restrictions and minimizes pressure drop.
- Anti-blowout stem: The stem in high-pressure ball valves is designed with an anti-blowout feature, which prevents the stem from being blown out of the valve due to high pressure.
- Double block and bleed design: Certain high-pressure ball valves are designed with a double block and bleed feature, which allows for the isolation of both upstream and downstream flow, and also provides a means for venting or draining the cavity between the two seals.
Selecting a high-pressure ball valve
Materials
- Choose materials like carbon steel and stainless steel 316 for the ball valve’s construction, as they are strong and can withstand high operating pressures.
- To withstand pressure ratings and maximum allowable stem torque, use materials like a duplex or other high-strength materials with good resilient properties for the ball, seat rings, and stem. Carbon steel, stainless steel, or other low alloys can also be used.
- Select thermoplastic seat inserts such as Devlon V, Nylon, and PEEK for soft-seated ball valves for their wear resistance and low friction coefficient.
- Seals for high-pressure ball valves are primarily made of o-ring elastomers, and anti-explosive decompression requirements are mandatory. Alternatively, PTFE lip seals can also be used.
Standards
There are several standards that high-pressure ball valves can conform to, depending on the specific application and industry requirements. Some of the most common standards for high-pressure ball valves include:
- API 6D: API 6D specifies the requirements and testing procedures for pipeline ball valves used in the oil and gas industry. This standard covers valves with pressure ratings up to 10,000 PSI and temperatures ranging from -45 °C (-50 °F) to 121 °C (250 °F).
- ASME B16.34: ASME B16.34 covers the design, materials, testing, and inspection requirements for valves in general, including ball valves. This standard covers valves with pressure ratings up to 690 bar (10,000 psi) and temperatures ranging from -6 °C (-20 °F) to 537 °C (1000 °F).
- ISO 17292: ISO 17292 covers metal ball valves used in petroleum, petrochemical, and natural gas industries. It specifies the requirements for materials, design, manufacturing, testing, inspection, and marking of the valves. The ISO 17292 standard covers valves with pressure ratings up to 10,000 PSI and temperatures ranging from -29 °C (-20 °F) to 200 °C (392 °F).
- ANSI/FCI 70-2: ANSI/FCI 70-2 covers ball valves' testing and inspection requirements. This standard includes tests for seat leakage, hydrostatic shell testing, and performance at high temperatures.
Connection types
High-pressure ball valves are available in the following connection types:
- British standard pipe parallel (BSPP) threaded
- National pipe thread (NPT) threaded
- Compression type (DIN 2353/ISO 8434-1)
- Welding end
Valve seat rating
A valve seat rating pressure vs temperature graph displays the safe operating pressure, and temperature ranges for a specific valve seat material. The graph typically shows the maximum pressure the valve seat can withstand at different temperatures while maintaining a leak-tight seal. The pressure-temperature rating graph provides essential information for selecting the right valve material for a given application, ensuring the valve can operate safely and effectively under expected operating conditions.
The graph often determines the maximum pressure a valve seat can handle at a specific temperature. For instance, PTFE works at a maximum pressure of 41 bar (600 psi) up to 121 °C (250 𐩑F) (Figure 2). If the operating temperature is 149 °C (300 𐩑F) and the maximum pressure allowed is 41 bar (600 psi), the material can fail, leading to leakage, operational failure, or damage to the valve and the surrounding equipment.
Figure 2: Pressure vs temperature graph for PTFE
