Analysis on the cause of cold bending fracture of low temperature reheater serpentine tube of power station boiler

CHENG Dongyue; JIN Shuo; SUN Xudong; MA Linlin; CHEN Jichang

doi:10.7512/j.issn.1001-2303.2020.04.17

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Analysis on the cause of cold bending fracture of low temperature reheater serpentine tube of power station boiler
Vol. 50, Issue 4, Pages: 100-102(2020)
Published：2020
DOI： 10.7512/j.issn.1001-2303.2020.04.17
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DOI：

CHENG Dongyue, JIN Shuo, SUN Xudong, et al. Analysis on the cause of cold bending fracture of low temperature reheater serpentine tube of power station boiler[J]. Eletric Welding Machine2020, 50(4): 100-102. DOI： 10.7512/j.issn.1001-2303.2020.04.17.

摘要

某电站锅炉低温再热器规格是φ50.8 mm×4.0 mm

材料牌号SA213-T91。钢管在冷弯塑性变形超过90°时连续出现断裂现象。通过进行钢管化学成分分析、力学性能检测、金相和显微硬度分析以及断口形貌分析

确定冷弯断裂成因。结果表明:SA213-T91内表面碳含量偏高

造成钢管内表面硬度偏高

塑性急剧下降

导致冷弯时钢管弯角以脆性解理方式开裂。分析制造工艺发现

由于模铸坯制造时存在铸造偏析

头部未切净

致使管坯心部增碳

从而使钢管内表面发生增碳现象。

Abstract

A low temperature reheater specifications is φ50.8 ×4.0 mm and material trademark is SA213-T91.Continuous fracture of steel tube occurs when the cold bending plastic deformation exceeds 90°. Through the chemical composition analysis

mechanical property test

metallographic exa-mination

microhardness and fracture morphology analysis of steel tube

the bending fracture causes are determined. The high carbon content on the internal surface of SA213-T91 cases the high hardness and a sharp decline in plasticity of the internal surface of steel tube

resulting in steel pipe bending angle cracks by brittle cleavage when cold bending. Based on the analysis of manufacturing technology

casting segregation exists during the manufacturing of die casting billet

and the head is not cut clearly

resulting in the heart carburization in the tube blank and the carburization phenomenon on the internal surface of steel tube.