Introduction

Expansion joints, also known as pipe expansion joints, compensators, or expanders, are primarily used to compensate for the expansion and contraction of pipes caused by temperature changes. They are also used to compensate for the length required for pipe installation adjustments. They can compensate for and absorb the axial, lateral, and angular expansion and contraction caused by heat, as well as the deformation of pipes caused by equipment vibration, earthquakes, and ground subsidence, reducing the impact on the pipes.

Types of Expansion Joints

There are several major types, including corrugated expansion joints, sleeve expansion joints, and square natural compensation expansion joints, with corrugated expansion joints being the most common.

1. A pipe expansion joint where the pipe is bent into a U-shape or other shape, utilizing the elastic deformation capacity of the shape for compensation. Its advantages are good strength, long life, and on-site fabrication. Its disadvantages are large space occupation, high steel consumption, and high frictional resistance. This type of expansion joint is widely used in various steam pipes and long pipes.

2. A corrugated pipe expansion joint made of a metal bellows. It can expand and contract along the axial direction and allows for a small amount of bending. It is commonly used in pipelines for axial length compensation. To prevent exceeding the allowable compensation amount, protective tie rods or rings are installed at both ends of the bellows, and guide supports are installed on the pipelines connected to it. There are also angular and lateral expansion joints that can compensate for angular and lateral deformation of pipes. The advantages of this type of expansion joint are space saving, material saving, ease of standardization and mass production. The disadvantages are shorter lifespan. Corrugated expansion joints are generally used in pipes with low temperatures and pressures and shorter lengths. With the improvement of bellows production technology, the application range of this type of expansion joint is expanding.

3. A sleeve expansion joint consists of inner and outer sleeves that can move axially relative to each other. The inner and outer sleeves are sealed with a stuffing box. During use, the two end pipes are kept moving along the same axis. Guide supports are installed at both ends of the expansion joint. Its advantages are low fluid flow frictional resistance and compact structure; its disadvantages are poor sealing and high thrust on the fixed support. Sleeve expansion joints are mainly used for water pipes and low-pressure steam pipes.

Component Structure

Reasonable design of supports in the pipeline system is a necessary condition for ensuring the normal function of corrugated expansion joints. Different types of corrugated expansion joints have different requirements for pipeline supports.

Main Anchor Support

The main anchor support is installed on a piping system with one or more unconstrained bellows expansion joints. It must withstand the forces and moments applied to it from each pipe section connected to it. This includes the pressure thrust (blind flange force) generated by the internal pressure of the pipe, the forces and moments required to produce the required displacement of the expansion joint, the frictional forces generated by the adjustable guide support and directional guide support, and the weight of the pipeline and medium, fluid impact force. When using an unconstrained bellows expansion joint, the main anchor support must be installed in the following cases:

(1) Pipe blind end

(2) Change in flow direction of the medium

(3) Pipe branch

(4) Pipe diameter change, shut-off valve or pressure reducing valve in the pipe between two bellows expansion joints.

Secondary Anchor Support

The secondary anchor support is used to withstand all loads except the pressure thrust (blind flange force).

For straight pipe sections, the secondary anchor support is usually used to divide a longer pipe section between two anchor supports into several pipe section units, so that only one bellows expansion joint is installed between each pipe section, to ensure that the expansion joint can work normally.

Practical Application

Application of expansion joints in gas pipelines:

In gas pipelines, especially those from self-provided gas generator kilns, due to the inherent heat of the gas, the pipelines from the gas station to the kiln and the pipelines near the gas burner of the kiln have significant expansion and contraction due to gas temperature changes. Setting expansion joints is necessary to alleviate pipeline stress and thrust. Expansion devices and expansion joints are also often installed in long-distance pipelines in some cold gas stations to alleviate the thrust caused by thermal expansion and contraction.

Selection Methods

When purchasing pipe expansion joints, you must strictly follow the relevant data provided by the design department, select the type according to the specific parameters and requirements of the pipeline system, and take appropriate measures to ensure its long-term stable operation and safe use. The following data is required when purchasing:

1. Nominal diameter: Represents the standard diameter of the expansion joint, in millimeters (mm).

2. Working pressure: Refers to the maximum pressure that the expansion joint can withstand under normal operating conditions, in Pascals (Pa) or Megapascals (MPa).

3. Nominal length: Represents the standard length of the expansion joint, in millimeters (mm).

4. Expansion amount: Represents the maximum distance the expansion joint can compress or stretch in the axial direction, in millimeters (mm). 5. Temperature range: Represents the operating temperature range of the expansion joint, in degrees Celsius (°C).

6. Material: Represents the main material of the expansion joint, such as carbon steel, stainless steel, etc.

7. Connection method: Represents the connection method between the expansion joint and the pipe, valve, and other equipment, such as welding, flange connection, etc.