The compensation amount of expansion joint is an important index to measure its ability to absorb the displacement caused by thermal expansion and contraction in the pipeline system. In China, the relevant national standards for expansion joints mainly include GB/T 12777, which covers the general technical requirements for expansion joints of metal bellows.

According to the available information, the compensation amount standard of the expansion joint is as follows:

• The national standard GB/T 12777 (original version 1999, later updated to 2008 version) specifies the general technical specifications for metal bellows expansion joints, including the range of compensation amounts.

• The standard compensation amount mentioned in some specific application cases is 20 mm, which means that the expansion joint can be elongated or shortened by 20 mm in the axial direction to accommodate the displacement of the pipe.

However, this does not mean that the amount of compensation for all expansion joints is limited to 20 mm. In fact, the compensation amount of the expansion joint can be designed to be larger to adapt to different working conditions. For example, certain expansion joints may have a single-sided compensation amount of 130 to 200 mm (for DN200 and above pipes) or 100 to 130 mm (for DN200 and below pipes).

Compensation amounts are usually calculated and designed based on the actual operating conditions of the pipeline, including but not limited to:

• Coefficient of thermal expansion of pipe materials

• Variation range of operating temperature

• Length of the pipe

• Other factors that may cause displacement, such as mechanical vibration

When designing an expansion joint, it is also necessary to consider its possible pressure thrust on the fixed bracket, as well as other constraints of the pipeline system.

In short, although there is a minimum compensation amount specified by national standards, in fact, the compensation amount design of expansion joints will be adjusted according to specific applications and working conditions to ensure the safe and effective operation of pipeline systems. During the design process, the engineer will refer to the relevant standards and combine the specific parameters of the pipeline system to calculate the appropriate compensation amount.