Compensator, as a key component, is more and more widely used in thermal pipe network. However, if the compensator is not properly applied in the pipe network, it will cause damage to the whole pipe system, and even a vicious accident.

Because of its compact structure, large amount of compensation, small flow resistance, zero leakage, no maintenance and many other advantages, the compensator is more and more widely used in heat network. But it also has some disadvantages which are difficult to solve: for example, axial compensator produces pressure thrust on the fixed support, which results in the high cost of the fixed support, and the thin wall of the compensator can not withstand torsion, vibration and security. Equipment investment, strict design requirements, high construction and installation accuracy, often not up to life expectancy and a series of shortcomings. In view of these shortcomings of the compensator, and the construction personnel are not fully familiar with the compensator, so it is easy to cause accidents during construction and operation. Analyzing the causes of accidents, some accidents belong to the problems of manufacturing quality of compensator itself or improper selection of materials, some are problems of construction, and some of them belong to the problem of design layout. Most of the problems are due to the failure of calculation and unreasonable selection of compensation pipes.

The main performance of the compensator includes: compensation amount, elastic stiffness, compressive strength, stability, fatigue strength, etc. The general design of thermal pipe network requirements is to meet the strength, stability, and fatigue life premise, The larger the compensation, the better the stiffness. The compensator combination is divided into axial compensator, angular compensator, double pull rod compensator pipe system.The angle compensator and the compound rod compensator are more close to the force form of the natural compensation pipe system and the internal pressure thrust is not considered. The axial compensator is used because of the larger internal pressure and the large amount of compensation.

 The basic principle of bearing force of compensator support:

 Axial compensator force support is divided into main fixed support, secondary fixed support, guide support.

 Fixed support thrust calculation:

 The horizontal thrust of the main fixed support consists of three forces:

 Internal pressure thrust due to working pressure F=PA:

P is the working pressure and A is the effective cross-sectional area. The internal pressure thrust is determined by the effective cross section area and the working pressure, and it is directly proportional to the working pressure and the effective cross section area. In general, the internal pressure thrust of the compensator is larger.

 Elastic force generated by compensator stiffness PA=KfL:

K is the stiffness of compensator, L is the actual elongation of pipeline, f is the coefficient，. and the pretension is 0.5, otherwise it is 1.

 Sliding friction reaction between fixed supports qμl

q is the weight of the pipe, μ is the friction coefficient, l is the distance from the free end to the fixed end of the pipe.

 Horizontal thrust of main fixed supportt = internal pressure thrust + friction elastic force + elastic force

 If not concentric, the bending distance and lateral thrust of the fixed support due to eccentricity will also be taken into account.

When calculating the thrust of the fixed point, the forces on each side of the fixed point should be calculated separately and then synthesized. When the direction of both sides of the fixed point is the same, the vector sum of two forces is used as the thrust of the fixed point. When the direction of the two forces is opposite, the force with large absolute value subtracts 0.7 times of the force with small absolute value as the thrust of the fixed point.

 The guide support controls the movement along the pipeline or compensator to ensure that the pipe expansion acts on the compensator and that the pipeline does not lose stability.

The influence of the small displacement of the fixed bracket on the compensator:

Many pipe systems and even directly buried pipes are arranged as movable designs with small thermal displacements of fixed supports. In natural compensated pipe systems, the whole pipe system is involved in compensating deformation. The pipeline deformation is more uniform, this arrangement makes the pipe system good integrity, high reliability, and can reduce stress concentration. In the compensator system, the situation is very different, if not handled properly, the safety of compensator is greatly affected. In order to reduce the heat transfer of the heat bridge, the heat insulation material such as rubber plate is added between the inner and outer ring plates of the fixed ring, and the inner and outer ring plates are not welded, so they can move freely. When the fixed support is subjected to a large force or water hammer vibration, it will produce a certain amount of displacement, and sometimes the longitudinal micro displacement, which has a certain effect on the compensator, will have a torque effect on the compensator.