Must-read for Engineers: Low-temperature Design of Trunnion Ball Valves/Gate Valves (BS 6364) And Analysis of Limitations of Butterfly Valves

In the field of low-temperature engineering, the selection of valves is of crucial importance as it directly relates to the safety and efficiency of the system. The BS 6364 standard provides clear specifications for the design, manufacturing, and testing of low-temperature valves. This article will focus on exploring the low-temperature design features of TRUNNION BALL VALVES and GATE VALVES under the BS 6364 standard and compare the limitations of BUTTERFLY VALVES in low-temperature applications, so as to help engineers make wiser choices in projects.

I. OVERVIEW OF THE BS 6364 STANDARD

The BS 6364 is a specification for low-temperature valves issued by the British Standards Institution (BSI), applicable to valves within the temperature range from -50 °C to -196 °C. This standard covers types such as gate valves, globe valves, ball valves, and butterfly valves, and stipulates the requirements for valve design, material selection, manufacturing, testing, and marking. The core objective of BS 6364 is to ensure the reliability and safety of low-temperature valves under extreme conditions, especially in the transportation and storage of low-temperature media such as liquefied natural gas (LNG) and liquid oxygen (LO2).

II. LOW-TEMPERATURE DESIGN FEATURES OF TRUNNION BALL VALVES

(1) Structural Design
A TRUNNION BALL VALVE is a specially designed ball valve with a trunnion structure on its valve body, which facilitates installation and maintenance. In a low-temperature environment, the design of the trunnion ball valve needs to meet the strict requirements of BS 6364. For example, the valve must be equipped with an elongated valve cover or packing gland to ensure that the temperature of the valve stem packing remains within the allowable range of the material. This design can effectively reduce heat transfer and prevent the packing from failing at low temperatures.

(2) Material Selection
In a low-temperature environment, the performance of materials will change significantly. Trunnion ball valves usually adopt low-temperature-resistant materials such as austenitic stainless steel, which can still maintain good toughness and strength at low temperatures. In addition, the materials for the valve seat and sealing surface are also specially treated to ensure good sealing performance at low temperatures.

(3) Testing Requirements
According to BS 6364, trunnion ball valves need to undergo a series of low-temperature tests, including shell tests, sealing tests, and operational performance tests. These tests aim to verify the sealing performance and operational flexibility of the valves under low-temperature conditions. For example, in a liquid nitrogen environment at -196 °C, the valve needs to undergo multiple on-off operation tests to ensure that it will not get stuck under extremely low temperatures.

III. LOW-TEMPERATURE DESIGN FEATURES OF GATE VALVES

(1) Structural Design
GATE VALVES also need to follow the design requirements of BS 6364 in low-temperature applications. Their valve covers usually adopt an elongated design to prevent heat from being transferred from the valve stem to the packing. In addition, the design of the gate valve also needs to consider the flow direction of the medium and the operating angle to ensure smooth operation in a low-temperature environment.

(2) Material Selection
The material selection for low-temperature gate valves is equally crucial. The main components such as the valve body, valve cover, and valve stem usually adopt low-temperature-resistant steel, such as low-temperature carbon steel or stainless steel. These materials have good mechanical properties and resistance to brittleness at low temperatures and can withstand the pressure and temperature changes of low-temperature media.

(3) Testing Requirements
The testing requirements of BS 6364 for low-temperature gate valves are similar to those for trunnion ball valves, including low-temperature sealing tests and operational performance tests. These tests ensure that the gate valves can be reliably closed and opened in a low-temperature environment while preventing medium leakage.

IV. LIMITATIONS OF BUTTERFLY VALVES IN LOW-TEMPERATURE APPLICATIONS

(1) Sealing Performance
The sealing performance of butterfly valves is relatively weak in a low-temperature environment. Since the sealing of butterfly valves mainly relies on the contact between the disc and the valve seat, low temperatures may cause the sealing material to become brittle, thus reducing the sealing effect. In addition, the structure of butterfly valves is relatively compact, and it is difficult to design elongated valve covers or packing glands like ball valves or gate valves, which limits their thermal isolation ability at low temperatures.

(2) Operational Flexibility
The operational flexibility of butterfly valves may also be affected in a low-temperature environment. The disc of the butterfly valve needs to rotate within the valve body. Low temperatures may cause the lubricant to fail or the medium to freeze, thus increasing the operational resistance. In comparison, the designs of ball valves and gate valves allow for easier operation at low temperatures.

(3) Applicable Range
BUTTERFLY VALVES are usually suitable for medium and low-pressure systems, and their applicability in low-temperature and high-pressure environments is limited. Ball valves and gate valves, due to their structural design and material selection, are more suitable for use in high-pressure and low-temperature environments.

V. COMPARATIVE ANALYSIS

The following table compares the key features of trunnion ball valves, gate valves, and butterfly valves in low-temperature applications:

VI. CONCLUSION

In low-temperature engineering, the selection of appropriate valves is of crucial importance. When designed in accordance with the BS 6364 standard, TRUNNION BALL VALVES and GATE VALVES can provide excellent sealing performance and operational flexibility and are suitable for high-pressure and low-temperature environments. In comparison, BUTTERFLY VALVES have certain limitations in low-temperature applications, especially in terms of sealing performance and operational flexibility. When selecting valves, engineers should comprehensively consider the design features, material selection, and testing requirements of valves according to specific application scenarios and requirements to ensure the safety and reliability of the system.