Metal Expansion Joints usually used in heating pipe networks are sleeve expansion joints, square expansion joints and corrugated expansion joints. Therefore, the exchange research summed up the common problems and prevention methods of Metal Expansion Joint in the heating network.

1) The center of the sleeve expansion joint and the center line of the pipe are not on the same axis.
This situation will cause excessive friction between the sleeves, and affect the sealing performance when the heating network is running, and eventually lead to pipeline leakage. In the structure, you should refer to the installation method of the bellows. First, the pipe structure, and then install the Metal Expansion Joint after the pipe breaks at the location where the sleeve expansion joint is needed. In this way, although a small amount of pipes are wasted, the situation of different shafts can be effectively avoided.
2) No pre-stretching of square expansion joints.
By using the deformation elasticity of the Metal Expansion Joint to improve the compensation ability, the expansion joint can be pre-stretched to a certain length before being installed on the pipeline. This is the pre-stretching of the square expansion joint, also known as cold drawing. After cold drawing and installation of the expansion joint, the pipeline is subjected to tensile stress. When the expansion joint works, it becomes a compressive stress, but its absolute value is much smaller than the stress value that can be achieved without pre-tensioning, so the compensation capacity and service life of the expansion joint can be increased, and the compression of the expansion joint can also be reduced stress. Correct. The thrust of the fixed bracket. There are two cold drawing methods for expansion joints. One is to use a cold drawing device with bolts for cold drawing, and the other is to use a rod with a screw or jack to open the two vertical arms of the expansion joint to achieve cold drawing.
When cold drawing is performed using a cold drawing tool, a piece of wood or wood washer with a thickness equal to the pre-stretched amount is clamped in the gap of the cold drawing interface, and then the fixing ring is welded on both sides of the joint on the pipe wall, and then cold applied. The flange pipe of the puller is clamped on the fixed ring, and the protruding stud bolts are inserted into the flange pipe hole, tightened with a nut, and then tighten the wooden block. After the pipeline has been installed, remove the wooden block in the cold drawn block and tighten the nuts evenly to make the interface gap meet the corresponding welding requirements. After welding, the bolts can be loosened and the cold puller can be removed.
3) The position of the cold drawing port of the square expansion joint is not selected correctly.
If the location of the cold drawing opening of the square expansion joint is not selected correctly, it will directly cause the Metal Expansion Joint to tilt, which will seriously affect the safety of the pipe network. Therefore, the location of the cold drawn interface should be considered when installing the pipe. During the construction process, cold-drawn joints should be selected on the straight pipe section 2 to 3 m away from the bending start of the expansion joint, or the cold-drawn joint gap should be reserved at the adjacent pipe joints. The expansion joints should not be too close to the expansion joints before cold drawing. Whether the distance between the two pipes meets the cold-drawn value, then cold-drawn and welded.
4) The disassembly time of the corrugated expansion joint rod is too early.
Axial external pressure Metal Expansion Joint is equipped with a detachable fixed tie rod. It is strictly forbidden to remove the pull rod before installation on site. After installation, it must be removed. During the construction process, if the fixed tie rod is removed before installation, the factory-adjusted default value will be invalid, the relative displacement of the expansion joint is not limited, and the compensation displacement after installation cannot meet the pipeline operation requirements.
5) It is unreasonable to choose the cold tension position of the double tie rod corrugated expansion joint.
Before installation, the large tie rod expansion joints are usually cold-tightened 1/2 in the opposite thermal expansion direction to obtain greater work compensation capabilities. Therefore, the expansion joint is in a negative deformation state in the cold state. After the pipe is heated and stretched, the corrugated pipe deforms laterally through flexibility, and the expansion joint can present a working deformation state in appearance, and can compensate for the thermal expansion of the pipe.
When cold-tightening, you must pay attention not to install the cold tightness too close to the expansion joint, and do not allow the expansion joint to deform to match the cold tension of the pipeline to prevent other stresses, such as misalignment and uneven action on the bellows during installation. Strain the expansion joint.
6) The double tie rod corrugated expansion joints are installed horizontally to withstand additional gravity.
Due to the poor strength of the bellows, the rigidity is small and cannot withstand forces other than medium pressure. Therefore, when installing horizontally, the distance between the two ends of the Metal Expansion Joint and the near bracket should be shortened as much as possible to prevent the gravity of the pipeline from acting on the corrugated pipe, causing deformation or even damage to the corrugated pipe.
7) The prerequisites for system hydraulic test are not available.
When the system hydraulic pressure test is carried out according to the design requirements, the secondary fixed pipe frame equipped with the end of the compensation pipe shall be reinforced to prevent the movement or rotation of the pipe. It is impossible to use a fixed tie rod to transport on the expansion joint to replace the Metal Expansion Joint to withstand the test pressure. In the case of a pipe section pressure test, if the segmented blind end is an auxiliary fixing bracket, it must be temporarily strengthened to avoid pushing and overturning. It should be noted that the strictly controlled test pressure should not exceed 1.5 times the expansion working pressure.