基于裂纹尖端张开角含轴向穿透裂纹X80管道极限压力预测

准确预测含轴向穿透裂纹管道极限压力对其安全运行具有重要意义,但现有极限压力预测模型已不满足高韧性、高强度X80管道的评定需求。对含轴向穿透裂纹X80管道极限压力进行研究,建立含轴向穿透裂纹X80管道壳单元与三维实体单元数值模型,应用壳单元模型替代三维实体单元模型以简化分析过程并提高计算效率。基于含裂纹管道壳单元模型,选用临界裂纹尖端张开角作为断裂参量,分析初始裂纹长度、检测单元长度、管道壁厚等不同因素对极限压力的影响,提出极限压力预测修正模型。将基于修正模型的管道爆破压力预测结果与试验测试结果进行对比分析。结果表明,初始裂纹长度与极限压力呈负相关关系;而检测单元长度和管道壁厚与极限压力呈正相关关系,且壁厚与极限压力基本呈近线性关系;三者均对极限压力具有较为显著的影响。该模型具有更高的准确性,可用于高韧性、高强度薄壁X80管道的止裂设计。

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

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.