1/ expansion joint position setting problem

 

 

 

When an expansion joint is added to a fixed tube-plate heat exchanger supported by lug support, which position is more suitable for the expansion joint? If the expansion joint is added on the support and the support is on the low side, the expansion joint will bear the additional axial force generated by the heat exchanger's dead weight and reduce the stability of the equipment. The reasonable design is that the expansion joint should be set under the bearing, and when conditions permit, the center of gravity of the equipment should be placed under the support plane of the bearing as far as possible to improve the stability of the equipment.

 

 

 

 

2/ number of longitudinal welds of expansion joints

 

 

 

When the bellows are formed by the integral method, the number of longitudinal welds shall refer to the provisions in the table. The number of longitudinal welds shall refer to the provisions in the table when the sheet metal is used for piecewise welding half-wave integral stamping.

 

 

3/ expansion joint corrosion allowance problem

 

 

 

For carbon steel and low alloy steel, take C 2 1mm; When C 2 > 1mm, austenitic stainless steel should be selected (when stainless steel is not suitable, C 2 can be selected according to the design requirements of the container); For austenitic stainless steel, C 2 = 0mm is used when the medium is extremely corrosive.

 

 

 

4/ expansion joint fatigue life check

 

 

 

For the corrugated tubes of austenitic stainless steel, when usual R t s, the problem of low cycle fatigue is not considered. Otherwise, it is necessary to check the fatigue life. In GB16749-1997 austenitic stainless steel expansion joint in appendix A of displacement is according to the design temperature of 300 ℃, the fatigue damage number N = 4.5 x 10 4 times. Safety factor 15. Allowable cycles [N]=3000. When the design temperature of 300 ℃, the actual operation cumulative number of allowable cycle is equal to 3000 times, then we can choose according to appendix A lesser displacement.

 

 

 

If not design temperature of 300 ℃ or actual need total allowable cycles is not equal to 3000 times (allowable cycles selection range of 50 ~ 5000 times). The displacement shall be corrected by A factor of C N or C t on the basis of the specified values shown in appendix A. When calculating with SW6 software, if the expansion joint is made of stainless steel, it is also necessary to select whether the type of fatigue cycle load is temperature difference cycle load or mechanical cycle load.