Thermal compensators are widely used in thermal departments due to their reliable operation, good performance and compact structure. From the shape of a wave, a u-shaped, Ω shape, C shape expansion joint, etc., including u-shaped expansion joint applied most widely. In the following, I will explain the common problems in the design and manufacture of u-shaped single-wave expansion joints, so as to remind the designers that the failure of bellows expansion joints used in heating pipe network to reduce errors occurs during pipeline pressure test and operation. There are three main types of problems in pipeline pressure test:

(1) improper temporary support of the pipe system or unreasonable setting of the pipe system fixing bracket leads to the failure of the bracket and excessive deformation of the bellows;

 

(2) due to the insufficient safety margin of pressure or displacement considered in the bellows design, the bellows will produce instability deformation failure during the pipeline pressure test;

 

(3) the manufacturing quality of expansion joints is a problem. The failure of bellows during operation mainly takes the form of corrosion leakage and instability deformation, among which the corrosion failure is the most. From the anatomic analysis of corrosion failure bellows, it is found that there are two types of corrosion failure: pitting corrosion perforation and stress corrosion cracking. Chloride stress corrosion cracking accounts for about 95% of the whole corrosion failure. There are two types of bellows instability: strength instability and structure instability. The structural instability is the instability of the column of the expansion joint of the internal pressure bellows.