海洋石油平台导管架阴极保护的实施和改进

介绍了海洋石油平台导管架阴极保护的情况和检测结果。某平台导管架牺牲阳极阴极保护按照DNV-RP-401设计,并安装了一套阴极保护检测系统用来检测导管架的保护状况。导管架下水后阴极保护检测结果表明:管架下水时的电位约为-510~-530 m V(相对于Ag/Ag Cl参比电极,下同);EL-40 m处导管架在下水52 d后,电位为-789 m V,即将达到抑制腐蚀所需要的保护电位;EL-14 m处导管架在下水后36 d开始,极化速度增大,在下水52 d后,电位达到-736 m V,很快也能达到保护电位;而导管架EL-70.5 m和EL-84.1 m处在下水52 d后电位分别为-637 m V和-628 m V,极化缓慢,且没有明显使导管架快速极化至保护电位的趋势。导管架下水达21个月后,超过70.5 m水深的区域一直无法极化至保护电位,且水下较深处的牺牲阳极的发出电流也远大于浅水区阳极的发出电流。经分析其主要原因是由于设计时所选取的电流密度偏小,无法在导管架表面形成致密的钙质沉积层。为使导管架能达到保护电位,提出了牺牲阳极阴极保护的改造方案。

Sacrificial Anode Cathodic Protection of Platform Jacket and Improvement

The cathodic protection of jacket of marine oil platforms and inspection results are introduced. The sacrlhclal anode cathodic protection of the jacket of a platform was designed in accordance with DNV - RP - 401, and a cathodic protection monitoring system was installed to monitor the protection of jacket. The monitoring results of cathodic protection after the installation of jacket in the water showed that the potential of the jacket was about - 510 ~ 530 mV （ to Ag/AgC1 reference electrode）. The potential of jacket at EL -40m location was -789mV 52 days after being submerged in water, which would reach the protection potential required for corrosion inhibition. The polarization speed of jacket at EL - 14m location rose very fast 36 days after being submerged in the water and the potential reached - 736mV 52 days after going into the water which could also rapidly reach the protection potential. The potentials of jackets at EL -70.5 m and EL -84. lm locatlons were -637 mV and - 628mV respectively 52 days after being submerged in water. The polarization was very slow and there was no trend of accelerated polarization to protection potential. 21 months after jacket＇ s being submerged in the water, the location 70.5m under water was unable to polarize to protection potential. Whereas, the output current of sacrificial anode in deep water was much higher than that in the shallow water. The analysis found that it was mainly caused by the low design current density and dense calcium deposit layer could not form on the surface of jacket, which resulted in that jacket could not reach protection potential for a long time. The retrofit of underwater installation of sacrificial anodes has been recommended to improve polarization in the lower parts of the jacket to reach the protection potential.