【作者】 肖方虹；

【导师】 杨兆建；

【作者基本信息】 太原理工大学 ， 机械工程， 2003， 硕士

【摘要】 在石油化工装置中，经常使用由奥氏体不锈钢管推弯制成的弯头。弯头不仅能改变管线的方向，而且，因其刚度低于与之相连的直管，故可通过弹性变形吸收系统中由于热膨胀等因素产生的力和弯矩，因此弯头的受压管道中是很重要的部件。其中最有代表性的弯头材质是18-8不锈钢，其韧性大，容易加工，焊接性也特别好，而且也具有耐腐蚀和耐高温的特点，因此，使用场所极为广泛。 但是，弯头在弯制和使用过程中极易产生裂纹，致使装置出现故障，严重影响设备的正常安全运行，故不锈钢弯头开裂故障已成为弯头生产中需解决的问题。 本论文根据茂名石油化工公司炼油厂新建装置中正在使用的一批18-8弯头的开裂情况，制定了故障诊断试验研究方案，对弯头裂纹机理进行了全面的分析，确定了不锈钢弯头的裂纹成因：主要是弯头在弯制过程中成型温度太低，钢管在弯制过程中奥氏体因形变而产生诱导马氏体，这种硬而脆的马氏体组织使材料的塑性降低，强度提高，从而增大产品开裂的可能性，这种组织不经固溶处理，马氏体组织在氢的作用下产生氢诱导马氏体，从而使表面产生延迟裂纹。同时弯头在使用过程中，由于弯头冷加工产生加工残余应力和焊接残余应力，在含量偏高的CI离子环境中使用，应力腐蚀对裂纹的扩展有促进作用。 本论文还结合18-8奥氏体不锈钢弯头在推制过程中产生裂纹的原因进行了推弯工艺试验。结果表明，加热弯制弯头时，在热应力和加工应力的作用下，钢管受拉表面首先在机械加工刀痕处和氧化表面晶界产生微裂纹；同时温度和变形量是影响弯头开裂的重要因素，在高温下开裂对变形量的增加较为敏感，随温度的降低，允许的变形量明显的增加，故对温度和变形量必须加以综合考虑；试验表明，钢管表面的粗糙度对弯头的开裂有影响，在相同的温度下，光滑试件在更大的变形时才开裂，或者说变形量太原理工大学工程硕士学位论文相同时光滑试件允许在更高的温度下弯制。试验还表明，氧化性气氛对开裂有影响，在弯制时必须尽量减少氧化性气氛，从而降低热弯开裂趋势。更多还原

【Abstract】 To be seasoned with the specification of process piping with defer structure, It is frequently to use stainless steel bending elbow for the equipment of petrochemical industry. The representative material is 18-8 stainless steel, because of the tenacity, could be used diffusely, but the elbow could give severity influence to the formal and safety operation for equipment. To solve the problem of the crack of stainless steel elbow become into the difficulty of the production elbow.This thesis reflects the fact of crack for using 18-8 elbows in a new system by the refinery of Company of Maoming Petrochemical Corporation, the topic of testing and studying has been coming in existence, to roundly analyses the reasons of the crack on the elbow, find out that the main reason is: the very low temperature of molding courses the crack of the elbow during bending, the austenitic of the pipe deformed, induced the martinsite, because of processing without solid solubility. Therefore coursed the damages of hysteresis which named "natural crack", the crack bears upon the content of hydrogen which could course the brittleness, the crack might come up within 1 ~2 days, or might come up after many month, if the medium CI content higher than normal in the piping, it might quicken the cracks coming cup.This thesis combine the other reasons of cracks on the 18-8 austenitic stainless steel elbow during the bending with failure analysistestings, the results indicated: when heat it up to bend the pipe by the force of heating press and processing pressing, the light crack come up on the surface of the pipe of the pipe, at the position of a scar which left by the mechanical processing and the crystal boundary on the oxidized surface; the temperature and the deformation volume could bring seriously influence to the deformation volume under high temperature, The testing indicated that the heating bending and temperature brings influence to the percussive tenacity of the pipe. The coarseness of the surface of the pipe could give influence to the cracking: under the same temperature, the smooth testing pipe could be deformed under more forces, or under the same deformation volume, the smooth testing pipe could be bended in higher temperature. That means: the temperature and the deformation volume should be comprehensively considered.更多还原