Corrosion Cause Analysis And Corrosion Mechanism Research Of Buried Thermal Insulation Pipe

Based on the investigation of the corrosion status of buried thermal insulation pipe in service in an oilfield,the corrosion morphology of the anticorrosive insulation layer and the pipe body,the residual wall thickness and pitting depth were measured by the macroscopic and microscopic detection,and the field soil composition was analyzed to discuss the causes of corrosion;Then,an indoor simulation test device under the peeled coating was established.The main factors affecting the corrosion of buried thermal insulation pipes were studied by electrochemical test technology,and the corrosion mechanism was clarified.The results show that the main reasons for the corrosion of buried thermal insulation pipes are water seepage at the patch location,cathodic protection current shielding,aging of the anticorrosion layer and high operating temperature.The increase of temperature and salt content promoted the corrosion of buried thermal insulation pipes,and the existence of soil microorganisms accelerated the corrosion of pipes.However,with the increase of temperature,microbial activity decreased,and its influence on the corrosion of steel pipes weakened.The corrosion mechanism of buried thermal insulation pipeline is mainly reflected in the macroscopic galvanic corrosion under the peeling coating.In other words,the pipe section at the damaged part of the anticorrosion layer acts as the cathode and has the cathodic protection effect,while the pipe section far away from the damaged part acts as the anode and has the contact corrosion effect.The most serious corrosion site and the distance from the damaged area depends on the effective distance effect of the macrocorroded cell,which is affected by temperature and the salt content of the medium.With the increase of temperature,the potential difference and coupling current density of the galvanic cell increase,and the corrosion of the anode area intensifies.As the salt content increases,the most severely corroded sites move away from the point of damage.