Research On Evaluation Of Corrosion Defects And Reinforcing Technology For Qing-Ha Oil Pipeline

With the years increasing of pipelines have been in service, corrosions in pipelines are becoming more and more seriously. Up to now, the standards about evaluation methods which focus on defects of corroded pipeline and repairing technology are still not perfect, that make it uncertainty on how to assess and repair the oil pipelines, and the running costs for the pipelines are expensive. Now the repairing methods deal with corrosion defects of oil pipelines are mainly to use welding methods traditionally.They haven't got some unified standards, just do it according to themselves experiences. The assessment methods about the result which with different repairing ways to reinforce pipelines are developing. We are still lack of evaluation standards.This article is on the basis of testing, analyzing, numerical simulation and test methods for crackdown, which is aiming at Daqing-Haerbin oil pipeline outside structure of investigation and analysis, different types of injury and defects are integrated evaluated. Strength calculation and striking test are done on the pipe body, this may provide a support to assess the corrosion defects and develop the repairing method of Qing-Ha oil pipeline.Statistical and analysis based on magnetic flux leakage inspection data on Qing-Ha oil pipeline, and field excavation checking, indicates that the metal loss of Qing-Ha pipeline is mainly because of the corrosion defects take placed on the pipeline outside wall. the length more than 100 mm and width more than 40°of corrosion defects take up more than 97% of serious corrosion defects, corrosion areas mostly locate near the pipeline girth welds along axial direction (coating mending position), and on the lower part of the pipeline along Circumferential; the morphology of the corrosions area is deep on middle zone, shallow on edge zone, between the corrosion and non-corrosion areas are smooth transition.The results of trial of simulating and analyzing the tube's corrosion defects show that the maximum stress of the corrosion defects bearing-pressure ability of hose body appears in the state of min thickness. Along with the pipeline corrosion depth increasing, pipe maximum stress bear increase gradually after taking inner pressure, the range of increasing rate get accelerate, pipeline's residual strength value decreased gradually. With the increasing of defects length or the reducing of the width, the tube body maximum stress value increased, but the increase is small, when the defects width 100°and the defects length is more than 100mm, the width and length of different defects maximum stress value of pipeline body is not change so much, this shows that the defect depth affect on maximum stress and bearing-pressure ability much more than the defect influence degree on the length and width.Welding for reinforcing simulation show that, for all area and large area defects from the pipe, using welding to reinforce the defects, with the length's increasing of the reinforcement layer beside thickness increases, the pipe which have defected, it's maximum stress value of pipeline body is not change much. There is little effect on reinforcement form the dimension change of reinforcement-layer, and also because there is no mid-layer between reinforcing plate and pipeline, which is used for bearing. Therefore, there is no effect of reinforcement on the pipe where is defected, welding repair just play the role of substituting defects and taking the uphold stress job of pipeline.Carbon fiber reinforcing simulation show that even carbon fiber reinforcement layer with 0.5 mm thickness, the maximum stress of pipeline corrosion reduce greatly, this shows that carbon fiber reinforcing effect is obvious, and with carbon fiber reinforcement layer thickness increasing, the max stress value of pipeline corrosion continues to drop. With the depth of the corrosion defects increasing, the number of carbon fiber reinforcement layer will increase, while the number is immobile, when the defects' length and width is increasing. This phenomenon betrays that the crucial factor is corrosion depth which decides the number of carbon fiber reinforcement layer.Contrast suppress test and result of simulation suggest that the two sets of data is almost same, only have tiny difference, error in the range of 10%. This hint the result is gross correct. Suppress test and result of simulation demonstrate that after the pipeline is restore by carbon fiber, there is a obvious enhance in yield suppress of this pipeline, this result insinuate to all tube, carbon fiber has its power, and even restored to its original strength.