二蒸馏装置渣油管线失效原因分析

Analysis of Failure of Residue Oil Piping in No.2 Crude Distillation Unit

中国石油化工股份有限公司北京燕山分公司炼油三厂二蒸馏装置因减底泵出口渣油管线破裂,致使装置停工抢修。通过对失效管段测试分析,认为事故的直接原因是管线腐蚀减薄,管线内应力超出许用应力,导致管线发生韧性撕裂,同时限流孔板引起的偏流冲刷导致了严重的局部腐蚀;另一原因是加工含硫原油后管道的材质不能满足使用要求,腐蚀速率达到了0.5～2.0mm/a。为了适应加工劣质原油的需要,以加工原油硫质量分数为0.5%,酸值0.7 mgKOH/g为设计依据,对二蒸馏装置操作温度240℃以上管线、设备进行材质升级。通过材质升级前与后腐蚀速率对比看到,材质升级管线的腐蚀速率大幅下降,其中减底渣油腐蚀速率由0.157 4 mm/a下降为0.000 7 mm/a,达到了预期效果。

A fire occurred because of the cracking of outlet residue oil pipeline at the bottom of vacuum tower of No. 2 crude distillation unitin SINOPEC Beijing Yanshan Petrochemical Co. , Ltd. , and the unit had to be shutdown for maintenance. The analysis of the failed pipe section concluded that the direct causes of the fire accident were the toughness tearing of pipeline due to the corrosion thinning and internal stress of pipeline exceeding the allowable stress. At the same time, the erosion of deflected flow of orifice plate led to serious local corrosion. The main causes of the accident are that the metallurgy of the pipeline could not meet the operation requirement after unit began to process sulfur crude oils. The corrosion rate was as high as 0.5 - 2.0 mm/a. To meet the requirements of processing low - quality crude oils with 0.5 w% sulfur and 0.7 mgKOH/g acid value, the metallurgy of the pipelines and equipment operating at a temperature higher than 240 ~C was upgraded. The comparison of the corrosion rates before and after metallurgy upgrading showed that the corrosion rate of the pipelines of upgraded metallurgy was greatly reduced. The corrosion rate of residue oil pipelines was lowered to 0.000 7 mm/a from 0. 157 4 mm/a. Expected results have been achieved.