What are the causes of the wear of the riser and returner in a CFB boiler?

　　Thermal shock and periodic changes in particle circulation will cause the riser and returner to wear. Construction quality problems can also cause wear of the riser and returner, such as the uneven transition between the template and the inner wall caused by the uneven transition, the uneven transition between the straight section and the cone section, and the damage of the expansion joint.