Investigation On The Influence Of Cracks On The Strength Of Pipeline

Pipeline transport is one of the oil and gas transportations in our country,the pipeline affects the transportation efficiency and safety greatly as the most important part in this transportation system.From the large pipeline accidents occurred in recent decades we can find that the pipeline rupture caused by the crack is the most common and main reason.In the research of the crack,the three-dimensional crack is more reasonably,and the oblique crack is the most common one in real project,but there is little study on it.So it is very necessary to do research on the three-dimensional oblique crack,and there is an important meaning on the related problem in real project.For the nonpenetrating crack of the pipe,the stress field around the crack front is complex.It establishes pipe model with three-dimensional elliptical crack(axial crack and oblique crack)using ABAQUS and FRANC3 D based on the finite element method in this paper,and it calculates the stress intensity factor of the crack front.It also analyzes the influence on the oblique crack front by several main factors,and obtains the calculation formula of the oblique crack's stress intensity factor and related fracture criterion in a certain t/R.Besides,it compares the internal and external surface of oblique crack effect on pipeline safety.In the end of the paper,there is an analysis of the crack growth simulation about the three dimensional axial crack and oblique crack,and gets the corresponding laws through the analysis.The result shows that,it is reasonable and correct to use ABAQUS and FRANC3 D to establish three-dimensional elliptical crack method of the pipeline;the max KI of the oblique crack decreases with the increase of t/R,and the trend of the decrease is getting slower,it also has a linear growth relationship with the length of the crack 2a and the depth of the crack b,but the impact on the crack of the length of the crack 2a is not obvious.The maximum of the stress intensity factor will increase with the increase of the oblique angle,the trend of the decrease is faster in the beginning but slower in the last with the increase of,and it has significant increase when the angle ranges from 20°~80°,the trend of the increase is fastest at about 45°;it can get the calculation formula of the oblique crack's stress intensity factor and related fracture criterion,when the t/R is given;the max of the stress intensity factor of internal surface crack front is bigger than the one of the external surface in the same parameters,and the impact on the pipeline is more serious by the internal surface crack;the oblique crack grows at the plane which has an angle with the original crack surface,the crack grows steady,and the increase of KI and the growth length reaches maximum on the deep of the crack.Besides,the growth length gets to its maximum on the end of the crack,when the oblique angle is around 70°.