Life Extension Analysis Of Subsea Pipeline Form XJ30-2FDD To XJ24-3FDD

As time goes on,the operating load of offshore oilfield has increased,then the use of the life-extending subsea pipeline continuously increase.These pipeline subjected to the load such as wave and ocean current,the erosion of the internal and external environment,material aging,fatigue,as well as mutation effects and other kind of influencing factor,and this is bound to produce damage and resistance attenuation,and then it is possible lose efficacy during the probation period.This paper focus on the main factors affecting the safety of life-extending subsea pipeline:CO2 corrosion and design defet,we adopt to the method of numerical simulation,experimental research and theoretical analysis to research content as follows and obtain some relative conclusions:We established the feasibility of pigging subsea pipeline which has fatal defection caused by differention of diameter.Further analysis formulation of flow safeguard measures,mechanical pigging of reduced diameter seapipe was carried out in a gradual manner to smoothly scrape deposits,and at the same time verify that the subsea pipeline is subject to CO2 corrosion.Preliminarily determined the corrosion degree of the pipeline body by analyzing the corrosion products,morphological organization,and chemical analysis of the parent metal at key positions.Through mechanical analysis,it was determined whether the impact toughness of different pipe sections of the subsea pipeline meets the requirements of API 5L.The weld fatigue test further examined the fatigue limit of the subsea pipeline.Through the high-pressure dynamic corrosion inhibition rate experiment,the corrosion rate is reduced to 0.04 mm/a in the range of 70? to 90?,and the corrosion inhibition rate is maintained at 80%to 95%,which the corrosion rate is between 50%and 70%;lab microbial corrosion experiments show that the SRB propagation in the subsea pipeline is mainly in the second half of the submarine pipeline;at the same time,CO2 gas in the subsea pipeline is found not to affect the propagation of SRB,and corrosion inhibitors Combined use of fungicides will be more efficient than single.According to DNV RP-F101 standard and PCORRC method,the remaining strength of the XJ30-2 to XJ24-3 subsea pipeline in the maximum corrosion zone is calculated as 62.63 MPa and 60.69 MPa,respectively.The stress distribution at the corrosion defect was obtained by finite element simulation and the remaining strength in the maximum corrosion zone of the subsea pipeline was calculated to be 40.25 MPa.The calculated residual strength is much larger than the actual operating pressure of this pipe,also the thickness reduction of different pipe sections is at a safe level.Combined with the data obtained from the ROV subsea survey,which proved that the subsea pipeline can be continuely operated.