普光气田集输管材腐蚀评价及缓蚀剂加药工艺优化

Corrosion evaluation on tubular goods for linepipes and optimization of corrosion inhibitor injection in the Puguang Gas Field

普光气田H2S平均含量15.18%,CO2平均含量8%,且含单质硫。为解决该气田湿气集输工艺管材的腐蚀问题,参考NACE MR0177/ISO15156,规定了试样的制备方法,避免了因试样问题产生的评价结果偏差。评价条件增加了单质硫含量、介质流速两个条件,实现了对普光气田工况条件的模拟,解决了按NACE MR0175标准H2S分压大于1MPa时无法选材的难题。开展了L360抗硫管材的氢脆、硫化物应力开裂及电化学腐蚀的分析评价,结果表明,采用淬火加回火制造工艺、严格控制S(0.003%)、P(0.02%)元素含量、硬度小于248HV的L360管材,其抗硫性能满足使用要求;但在高含H2S、CO2且单质硫共存的条件下,L360抗硫管材电化学腐蚀严重,平均腐蚀速率达0.165 7mm/a,腐蚀产物主要为FeS,电化学腐蚀主要受H2S控制。因此对缓蚀剂加注工艺进行了优化,制订了一套预膜型缓蚀剂+连续缓蚀剂的实验室评价方法,规定了试片预膜处理的具体步骤,并优选出有机胺盐和季胺盐复配物为主的连续缓蚀剂+咪唑啉和吡啶衍生物为主的预膜缓蚀剂,现场应用后腐蚀速率控制在0.043 2mm/a。优选的L360抗硫钢和缓蚀剂在普光气田湿气输送集输工艺得到成功应用。

In the Puguang Gas Field,the natural gas contains the elemental sulfur as well as 15.18% of H2S and 9.54% of CO2 on average,so the corrosion prevention and control is essential to the tubes and pipes of wet gas gathering and transmission lines there.In view of this,based on the requirement of NACE MR0177/ISO15156,the L360QCS longitudinal submerged arc welding pipe is first selected as the study object,and the sulfur and flow rate are two additional conditions for the evaluation,simulating the working conditions in the Puguang Gas Field.An evaluation of sulfide stress corrosion cracking,hydrogen induced cracking(HIC),and electrochemical etching has been done on the L360QCS tubes.Results show that the quenching and tempering process can be adopted to control such tube material's components of sulfur at 0.02% and phosphorus at 0.003%,and its hardness less than 248 HV to meet the sulfur resistant needs.But under such environment of high H2S and CO2 as well as the elemental sulfur,the electrochemical corrosion will seriously occur on the L360 tubes with an average corrosion rate of 0.1657 mm/a and the corrosion product is FeS.Therefore,through the optimization of the corrosion inhibitor processing technology,an experimental evaluation method is developed for pre-filming corrosion inhibitors plus continuous corrosion inhibitors with the detailed procedures of pre-filming treatment of a corrosion coupon,and a continuous corrosion inhibitor is optimally selected composing of the mixture of organic amine and quaternary ammonium salts while a pre-filming corrosion inhibitor is selected made up of imidazoline and pyridine derivatives.In this way,the corrosion rate is controlled to be 0.0432 mm/a in an application case.The optimal L360 sulfur-resistance steel and the improved corrosion inhibitors have been successfully applied in the wet gas gathering and transmission lines in the Puguang Gas Field.