Prediction of limit pressure in axial through-wall cracked X80 pipeline based on critical crack-tip opening angle

Key words:  X80 pipeline  axial through-wall crack  critical crack-tip opening angle  limit pressure  prediction model

Abstract:

How to accurately predict the limit pressure of the pipeline with axial through-wall cracks is of great significance to its safety working conditions. However, the existing limit pressure prediction models can 't meet the requirements of X80 pipelines which are of high toughness and high strength. Considering this feature, the limit pressure of X80 pipeline with axial through-wall cracks is studied in this paper. Firstly, both of the shell element and three-dimensional solid element are used in the modeling process. The shell element model is chosen to displace the three-dimensional element model for analysis, in order to simplify the calculation and improve the computational efficiency. Based on the shell element model, the critical crack-tip opening angle (CTOA) is selected as the fracture criterion, and the effects of different factors such as the initial crack length, length of finite element, pipe wall thickness, are discussed. Finally, a modified model for the prediction of limit pressure is proposed. The burst pressure of pipelines predicted by the modified model is compared with that from the experimental results. The results show that there was a negative correlation between the initial crack length and the limit pressure, while the test element length and the wall thickness of the pipe were positively correlated with the limit pressure. What is more, the wall thickness is nearly linear with the limit pressure. And all of the three factors have a significant effect. The proposed model is more accurate than the existing one, and it can be used in the crack arrest design of thin-wall X80 pipes with high toughness and high strength.