Analysis On Glass Fiber Reinforced Polymer Repair For Pipelines With Circumferential Surface Crack

Pipeline is one of the most important structure styles in modern energy transposition field,oil&gas pipeline has especially be the energy lifeline for today's national economy development.However,because of the harsh conditons in the pipeline laying or service process,there will be various defects in the pipes inevitably.If the defects could not be repaired in time,at best,such defects would result in pipe leaks,at worst,the pipeline would burst out,which could cause incalculable loss to environment,personal safety and economy development.As an important representative of the various pipe defects,the rehabilitation technologies of pipes with circumferential surface cracks and similar defects have been paid greats concerns.As a new kind of pipe rehabilitation technology,because of the incomparable advantages to traditional pipe rehabilitation technologies,Glass fiber reinforced polymer(GFRP)technology has been widely applied in the repair of pipes with volume defects.However,researches on the GFRP repair effects on pipes with circumferential surface crack are less adequate.Accordingly,this paper studies on the circumferentially cracked pipe repaired with GFRP.By the experiment and numerical simulation research methods,comparative analysises of pipe states before and after repair were conducted under hydrostatic pressure and bending moment.The effects of GFRP parameters on repair effect were discussed in detail.The main researches are listed as follows:First of all,material performances of the high-strength glass fiber grid cloth/epoxy resin composite are tested,and the essential datas for pipe rehabilitation experiments and numerical simulations are collected.Bursting tests of the circumferentially cracked pipes with/without GFRP repair were respectively conducted under hydrostatic pressure-bending moment loads.The repair effects of the GFRP on circumferentially cracked pipe are analyzed.The results indicate that when the load condition can not make the pipe steel yield,GFRP repair effect is unsatisfactory,however,if the load condition is high enough to make pipe steel yield,GFRP repair can stop the yield of pipe repaired effectively.Besides,GFRP can also raise the failure load value of the circumferentially cracked pipe.Secondly,based on the dimension parameters of the experiment pipes,finite element models of the circumferentially cracked pipes are established.According to the Newman-Raju theoretical formula,the accuracy of the finite element model is verified.The results show that expanding the experiments by numerical simulation method is feasible.Third,by the numerical simulation method,two series of pipe models with the same depth,different length and the same length,different depth circumferential surface cracks were analyzed.The deepest point J integral values of different size cracks were calculated.The results indicate that the J integral change rule with load has nothing to do with the crack size.Further,the relationship between crack J integral and the axial strain of crack central side steel was also researched,the results show that,nothing to do with the crack size,the two change rules with load have definitely pertinence.Finally,according to the experiment results,the accuracy of the finite element models with GFRP repair is verified.Referring to the Simulation results of the models without GFRP repair,the influences of GFRP width,thickness and viscose modulus on repair effect are provided by series of numerical simulation experiments.Finally,some reasonable suggestions to the selection of the GFRP dimension when GFRP is applied to repair pipes with circumferential surface crack are proposed.