Multiphase Subsea Pipeline Internal Inspection And Assessment Technique

The exploration and development of marine oil and gas field has become the focus of China’s oil industry. Oil and gas transportation is the main task of subsea pipeline. The conveying medium of multiphase subsea pipeline are oil, gas and water, due to the complexity of flow regine, it often causes terrible corrosion. So, we need to conduct regular inspection and adaptability evaluation for the subsea pipeline, confirm the risk size, make maintenance plan, to ensure the safe and effective running of submarine pipeline. In this paper, the study is mainly based on pipeline detection technology in the domestic and overseas and internal corrosion assessment method.The different detection technology of pipeline internal corrosion has its own advantages and disadvantages in weld, cracks and local deformation detects. This paper compares and analyzes Magnetic flux leakage method and ultrasonic method, which are mainly used in subsea pipeline inspection technologies. The former is suitable for oil and gas pipeline, low environmental requirements, and is remarkable for mezzanine, slight pitting, annular weld crack detection; but the detection precision is affected by the thickness. The latter is high in detection sensitivity and has advantage in the detection of sand holes, groove corrosion, metal grinding loss, but it needs liquid coupling agent and high cleanliness of pipeline, does not apply to gas pipelines. By studying the case of Panyu oil field PY4-2 to FPSO marine pipeline successful implementation of ultrasonic detection, we put forward important options in Panyu oil field subsea pipeline corrosion condition assessment and integrity management. So before the detection of pipeline, people should take fully research, consider pipe process conditions, testing standard and related specifications, choose the appropriate testing equipment, establish the relevant supporting facilities and contingency plans, form the regular submarine pipeline detection and maintence plan that is corresponding to standard, to ensure the safety of subsea pipeline to run effectively.For the unsuitable direct detection pipeline, internal corrosion direct assessment is possible. Multiphase flow parameters simulation of pipe and the choice of corrosion rate prediction model is the core of direct assessment method. This paper takes simulated corrosion with OLGA software three-phase flow module and corrosion module, to research the effect of temperature,CO₂ partial pressure, gas liquid ratio, pipe parameters such as angle, water cut on the pipe corrosion rate. Combining with multiphase flow pipeline internal corrosion experiments, to discuss the influence of temperature, CO₂ partial pressure and gas liquid ratio on CO₂ corrosion rate. Experimental studies have found that with the increase of temperature, corrosion speed is rising and then reducing, the CO₂ partial pressure has two sides effect on corrosion rate, temperature affects the pressure critical point, gas liquid rate affect the corrosion rate through two phase flow state, and the influence of slug flow is most serious.