Design Specifications for Cryogenic Floating Ball Valves: Special Material Requirements in LNG Storage Tank Applications

I. The Role of Cryogenic Floating Ball Valves in LNG Storage Tanks
The design temperature of LNG storage tanks is usually between -165°C and -196°C. Such an extremely low temperature environment imposes extremely high requirements on the materials and design of valves. CRYOGENIC FLOATING BALL VALVES are mainly used to control the flow of LNG and ensure reliable sealing and operation under low temperature conditions. Their main functions include:
• Sealing performance: Prevent LNG leakage and ensure the safety of the storage tank system.
• Low-temperature performance: Materials must be able to maintain mechanical properties under extreme low temperatures to avoid brittle fracture.
• Operational reliability: Valves need to achieve flexible operation in a low-temperature environment and avoid jamming or failure caused by temperature changes.

II. Design Specifications for Cryogenic Floating Ball Valves
(A) International Standards and Specifications
The design of CRYOGENIC FLOATING BALL VALVES usually needs to follow a series of international standards and specifications to ensure their performance and safety. These standards include but are not limited to:
• API 608: The American Petroleum Institute standard, which stipulates the basic design requirements for ball valves.
• ASME B16.34: The American Society of Mechanical Engineers standard, which involves the pressure and temperature ratings of valves.
• ISO 28921-1: The International Organization for Standardization standard, specifically targeting the design of cryogenic valves.
• BS 6364: The British standard, applicable to the design and testing of cryogenic valves.

(B) Design Features
• Cryogenic treatment: Key components of the valve (such as the valve body, valve seat, etc.) need to undergo special cryogenic treatment to relieve stress and ensure the performance of materials at low temperatures.
• Sealing design: Adopt a double-contact circular elastic valve seat design to optimize the contact area between the ball and the valve seat and ensure the sealing performance under low temperature conditions.
• Fireproof and antistatic design: Considering the flammability of LNG, valves need to have fireproof and antistatic functions to prevent hazards caused by fire or electrostatic accumulation.

III. Special Material Requirements in LNG Storage Tank Applications
(A) Inner Tank Materials
The inner tank of an LNG storage tank directly contacts the cryogenic liquid, so materials with excellent low-temperature toughness and mechanical properties need to be selected. Common inner tank materials include:
• 9% Ni steel: This material can still maintain good mechanical properties at a low temperature of -162°C and is the preferred material for the inner tank of LNG storage tanks.
• Austenitic stainless steel: Such as 304 and 316, which have good corrosion resistance and low-temperature performance.
• Aluminum alloy: In some specific applications, aluminum alloy is also used for the inner tank, but its strength and toughness at low temperatures need to be ensured.

(B) Outer Tank Materials
The outer tank is mainly used to provide structural support and thermal insulation functions and usually adopts the following materials:
• Prestressed concrete: It has good compressive performance and thermal insulation effect and is commonly used for the outer tank of large LNG storage tanks.
• Carbon steel: Used for the moisture-proof plate and some structural components of the outer tank and requires anti-corrosion treatment.

(C) Insulation Materials
To reduce heat transfer and maintain the low-temperature state of LNG, high-performance insulation materials need to be filled between the inner and outer walls of the storage tank. Common insulation materials include:
• Expanded perlite: It has good thermal insulation performance and a low thermal conductivity.
• Foam glass bricks: Used for the thermal insulation of the tank bottom and the inner tank wall and has a relatively high bearing capacity.

IV. Comparative Analysis of Materials
(A) Comparison between 9% Ni Steel and Austenitic Stainless Steel
Characteristics 9% Ni Steel Austenitic Stainless Steel
Low-temperature toughness Excellent, suitable for -162°C Good, but attention should be paid to low-temperature brittleness
Strength High strength, suitable for high-pressure working conditions Lower strength, suitable for low-pressure working conditions
Corrosion resistance General, requiring additional anti-corrosion measures Excellent, with strong corrosion resistance
Cost High Medium

(B) Comparison between Prestressed Concrete and Carbon Steel
Characteristics Prestressed Concrete Carbon Steel
Thermal insulation performance Excellent, suitable for large storage tanks Poor, requiring additional thermal insulation measures
Compressive strength High Low
Corrosion resistance General, requiring anti-corrosion treatment Poor, requiring anti-corrosion coating
Cost Medium Low

V. Summary
The application of CRYOGENIC FLOATING BALL VALVES in LNG storage tanks needs to strictly follow international design specifications, and appropriate materials should be selected according to the working conditions. 9% Ni steel and austenitic stainless steel are the main material choices for the inner tank, while prestressed concrete and carbon steel are commonly used for the outer tank. Through comparative analysis, we can better understand the advantages and disadvantages of different materials, so as to make more reasonable choices in practical applications. With the continuous development of the LNG industry, the requirements for CRYOGENIC FLOATING BALL VALVES and storage tank materials will also become higher and higher. In the future, further research and development of high-performance cryogenic materials will be needed to meet the needs of the industry's development.