大型焦炭塔的腐蚀分析及防护措施

Corrosion analysis and protection measures of large-scale coke drum

关键词:  延迟焦化  大型  焦炭塔  腐蚀  热疲劳  防护

Key words:  delayed coking  large-scale  coke drum  corrosion  thermal fatigue  protection

摘要:

某炼油厂Φ9 800 mm大型焦炭塔在投入运行后,锥段内壁出现点蚀坑,环焊缝出现裂纹。对腐蚀部位取样分析,结合生产工艺特点,认为产生点蚀坑的主要原因为:高温环境下焦炭塔母材的高温抗力下降,在交变载荷和冲击性载荷作用下,母材产生高低温冷热疲劳和蠕变开裂,裂纹交叉部位剥落形成蚀坑。锥段单侧进料、较短的生焦周期等因素则加速了蚀坑的产生。产生环焊缝裂纹的主要原因为18 h生焦周期产生了较强的热机械疲劳。针对上述腐蚀原因,从工艺操作、材料升级等方面提出了升级锥段材质、延长生焦周期、延长大吹汽时间、提高焦炭塔预热终温、改变进料方式等防护措施。上述措施实施后,焦炭塔的腐蚀情况得到明显改善。

Abstract:

The Φ9 800 mm large-scale coke drum of a refinery appeared corrosion after commission. The corrosion was mainly shown as pitting corrosion of cone section inner wall and cracks in the girth weld. Through sampling and analysis of the corrosion area, and combining with the characteristics of production process, it was considered that the causes of pitting included:Under the high temperature, the high temperature resistance of coke tower was decreased. Under the action of alternating load and impact load, hot-cold fatigue and creep cracking were occurred on the parent material. The etch pits were formed while the part of the cracks cross was spalled. Also, the single-side feeding of cone section and short coking cycle accelerated the formation of the pitting. The main cause of cracks in girth weld was thermal mechanical fatigue which caused by an 18 hour coking cycle. The protection measures were put forward for corrosion reasons from the aspects of process operation and material upgrading etc. The measures included upgrading the material of the cone section, prolonging the coking period and steam blowing time, increasing final preheating temperature of coke drum and changing the feed mode, etc. After the implementation of above measures, the corrosion of the coke drum was obviously alleviated.