Analysis of Failure Mode and Construction Improvement of Spray Tubes in Boiler Desuperheater

Abstract

With macrographic examination, SEM observation and fracture quantitative analysis technology, the fracture fractography of a spray tube with both the mechanical stress and the thermal stress in a boiler desuperheater of a power plant was interpreted, and the failure mode and the cause were researched. Results showed that rupture of the spray tube was due to the fatigue, and further, the thermal mechanical fatigue. The alternating bending stress and thermal stress were main factors of the fracture failure. The shallow surface thermal fatigue cracks in tube inner wall were induced by thermal stress. When the thermal mechanical fatigue crack grew up steadily to the shallow surface cracks zone, fast growth occurred and the local fast fracture zone generated which had different fractographies with final fast fracture zone of the normal fatigue fracture.