The retractable length standard of the extension joint (compensator) depends on its type, design, and the specific working conditions of the application. Different standards and specifications set corresponding technical parameters for different types of extension joints to ensure their safe and reliable operation under specific working conditions. Here are some general guidelines and common standards regarding the retractable length of the extension joint:
General guiding principles
Material Properties：
The material of the expansion joint determines its maximum allowable expansion and contraction. For example, metal bellows typically have higher elasticity and can withstand larger deformation; While rubber or plastic materials are suitable for smaller displacements.
Working conditions：
Temperature, pressure, media type, etc. all affect the maximum extension length of the extension joint. In high temperature and high pressure environments, the design of expansion joints must be more conservative to ensure long-term reliability.
Installation location：
Where the extension joint is installed will also affect its retractable length. Places close to heat or vibration sources may require greater compensation.
Fixing and guiding device：
Reasonable setting of the fixed bracket and the guide bracket can effectively control the movement direction of the telescopic joint, avoid unnecessary lateral force or torsion, and thus improve its compensation effect.
Common criteria
International Organization for Standardization (ISO)：
ISO 15692:2017, Metal Bellows Expansion Joints for Piping Systems, specifies the design, manufacture, inspection and acceptance requirements for metal bellows expansion joints, including the maximum allowable expansion and contraction.
American Society of Mechanical Engineers (ASME)：
ASME B16.35 Bellows Expansion Joints provides standard dimensions, performance requirements, and test methods for bellows expansion joints, covering multiple types of bellows expansion joints and their maximum allowable expansion and contraction.
European Standard (EN)：
The requirements for expansion joints are included in the EN 13480 series of standards for industrial piping systems, such as EN 13480-3, which describes the rules for design and calculation of expansion joints in detail.
China National Standard (GB/T)：
GB/T 12777 "General Technical Specifications for Expansion Joints of Metal Bellows" is a technical specification formulated by China for expansion joints of metal bellows, which specifies the maximum allowable expansion and contraction amount of different specifications and models.
Specific numerical examples
Specific scalable length values vary depending on product model, manufacturer, and application scenario. Here are some typical values for reference:
Axial bellows expansion joint: In general, the axial compensation amount of a single corrugation is about twice the depth of the corrugation. For multi-corrugated structures, the total compensation amount is the sum of each corrugation compensation amount. For example, a three-corrugated expansion joint with a wave depth of 10 mm has a maximum axial compensation of about 60 mm.
Sleeve expansion joint: The maximum amount of compensation for a sleeve expansion joint is usually determined by the stroke of the sliding sleeve. Depending on the specific design, common maximum compensation amounts can range from tens to hundreds of millimeters.
Rotary Joint: This type of compensator is mainly used for rotary joints, and its compensation amount is more reflected in angular change than linear displacement.
Design Considerations
Pre-stretching or compression：
For some expansion joints that require "cold tightening", appropriate pre-stretching or compression is performed at installation according to design requirements to achieve optimal compensation at operating temperatures.
Compensation needs assessment：
The expected displacement of the piping system should be evaluated in detail before selecting the expansion joint and the required amount of compensation should be determined accordingly. This can be achieved by thermodynamic calculation, finite element analysis and other means.
Conclusion
There is no uniform standard value for the retractable length of the extension joint, but it depends on the comprehensive consideration of many factors. In practical application, it is recommended to refer to relevant international, national or industry standards, and combine with specific working conditions and technical requirements to select the appropriate expansion joint. In addition, it is also very important to work closely with the manufacturer and obtain professional technical support. Through reasonable selection and design, the expansion joint can be ensured to perform optimally under various complex working conditions.