【作者】 陈严飞；

【导师】 周晶； 李昕；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2009， 博士

【摘要】 随着我国海洋油气资源的开发,海底管道对海上油气田的开发、生产和产品的运输起着关键性的作用,被称为海上油气田的“生命线”,海底管道建设日益增多。海底管道所处的海洋环境恶劣,管道发生腐蚀损伤不可避免。管道发生腐蚀后,会引起管壁整体或局部变薄,使得管道的静态和动态抗力减小,若不及时更换或维修,会引起海底管道的破坏和原油泄露事故。腐蚀是引起海底管道破坏的主要因素之一,为了避免此类事故的发生,需要准确预测腐蚀管道的剩余强度,及时正确决策腐蚀海底管道是否能继续运行。因此研究海底腐蚀管道在工作荷载以及环境荷载作用下的破坏机理和极限荷载具有重大的理论意义和实用价值。基于经典的Tresca和Mises屈服准则,给出了完好管道和无限长腐蚀管道极限内压荷载解析解。建立了海底管道非线性分析模型,分析了轴向腐蚀管道在内压荷载作用下的破坏机理,提出了基于参考应力的应力失效准则来确定管道的失效内压,探究了腐蚀深度、腐蚀长度、腐蚀宽度、腐蚀位置、轴向应力、管材等参数对管道极限内压荷载的影响,与现有腐蚀管道计算方法进行了比较,并基于计算结果回归了轴向腐蚀管道失效内压荷载计算公式,通过与实验数据对比,验证了本公式的适用性和准确性。研究了轴向和环向相邻腐蚀管道在内压荷载作用下的破坏机理和极限内压荷载的计算方法,研究了腐蚀轴向间距、环向间距和腐蚀深度等参数对管道失效模式和失效内压的影响,提出了轴向相邻腐蚀相互作用准则和环向相邻腐蚀相互作用准则。基于轴向和环向相邻腐蚀相互作用准则,提出了轴向投影和环向投影的双向投影的方法,采用等效长度、等效宽度、等效深度的概念,给出复合相邻腐蚀管道极限内压荷载计算步骤,发展了群腐蚀管道的极限内压荷载计算方法,为复杂腐蚀形式的管道的剩余强度评估提供了一定的参考依据。基于理想弹塑性模型,给出了管道在剪力、扭矩、内压、轴向力联合作用下管道极限弯矩荷载无量纲一般解析解,探究了剪力、扭矩、内压和轴向力对管道极限弯矩荷载的影响,给出了相互作用曲线和曲面。基于线性强化弹塑性模型,给出了轴向力作用下管道极限弯矩荷载的解析解和近似解;并采用幂次强化模型,给出了内压和轴向力联合作用下管道的极限弯矩荷载计算方法。通过与实验数据对比表明,基于理想弹塑性假设的解析解预测值可以作为联合荷载作用下管道的极限弯矩荷载的下限值。当管道受到轴向拉力作用时,考虑管材的应变强化作用,管道极限弯矩荷载的预测值与实验值吻合更好。基于Hill屈服准则,考虑了管材的各向异性,推导了不规则腐蚀缺陷管道在内压和轴向力联合作用下极限弯矩荷载解析解,并编制了相应的通用程序CPC。为了腐蚀管道评估的工程实用性,发展了等深度、椭圆和抛物线三种理想化形状腐蚀缺陷管道的解析解,通过算例验证了解析解与广义解结果具有很好的吻合性。探究了腐蚀深度、腐蚀宽度和腐蚀形状等参数对极限弯矩荷载的影响。研究表明除了腐蚀深度和宽度外,腐蚀形状对极限弯矩荷载有显著影响,将实际腐蚀简化为等深度腐蚀,将会过低估计管道的极限弯矩荷载。更多还原

【Abstract】 Submarine pipelines, which serve as the arteries of the oil and gas industry, have been widely accepted as one of the most economical ways of transporting oil and gas over long distances. These pipelines typically connect an inlet, such as an offshore platform or an onshore compressor station, to an outlet, which can be another offshore platform or an onshore receiver station. Due to the harsh environment that most of these pipelines are located in and the corrosive medium that these pipes are transporting, deterioration due to corrosion is inevitable. Consequently appropriate residual strength evaluation of corroded pipelines is vitally important. Timely repair or replacement can avoid over deterioration and failure which would result in not only large economical loss but also severe environmental pollution.The burst capacity of submarine pipeline with longitudinal corrosion defects is investigated with the intention of the optimizing the cost effectiveness in corrosion allowance limit design and residual strength assessment of corroded pipeline. Based on the elastic-plastic, large-deformation finite element method, the failure behavior and limit load of submarine pipeline with longitudinal corrosion defect subject to internal pressure are studied. The effect of corrosion depth, length, width and location on burst capacity is also discussed. Based on the FEA results, a set of regression equations are proposed for burst capacity prediction of submarine pipeline with longitudinal corrosion defects. The limit loads predicted by the proposed solutions are compared with those predicted by various solutions provided by the assessment codes and literatures. Furthermore, the predicted limit loads are compared with the laboratory test results and it is concluded that solutions proposed in this paper are in extremely good agreement with the experimental test data, which will give more accurate results than the existing methods.Based on the elastic plastic finite element method, the failure behavior and burst capacity of submarine pipeline with interacting corrosion defects i.e. longitudinally and circumferentially aligned double corrosion defects are analyzed. The effect of corrosion depth, longitudinal and circumferential spacing between double corrosion defects on failure behavior and burst capacity are investigated and the corresponding interaction rules for longitudinally and circumferentially aligned corrosion are proposed. Through the projection of the corrosion profile on the longitudinal and circumferential direction, a new method is proposed for pipeline with more general interaction type named as compounded aligned corrosion defects. Furthermore, the evaluation procedure is extended for pipeline with colonies of corrosion defects. Due to the incorporation of the effective length, width and depth in those solutions, the resistance effect of uncorroded region between each corrosion defects can be reasonably taken into account. Therefore, the procedure is proved to be able to yield more accurate predictions than those in current assessment codes after compare with the experimental results.A set of nondimensional solutions for predicting the full plastic bending capacity of intact pipes in the presence of shear force, torsion moment, internal pressure and axial force is presented based on Mises yield criteria. Using Hencky’s total strain theory of plasticity, bending capacity of pipes can be determined analytically and numerically assuming an elastic-linear hardening and power law hardening material. Good comparison is observed when bending capacities obtained from analytical solutions are compared with experimental results from full-size tests of steel pipes. It is shown that strain hardening pipes yield higher bending capacity than pipes with assumed elastic-perfectly plastic material, as commonly assumed in current code, which may underestimate the bending capacity of steel pipes, especially for pipeline in the presence of axial tension.Bending capacity of corroded pipes can be determined analytically assuming a full plastic failure mode for the pipe. A set of generalized solutions for bending capacity of the pipeline can be developed if the shape of the corrosion defect is known a priori. The generalized solutions derived in this paper are able to account for the combined action of internal pressure and axial force. For practical purposes, the generalized solutions thus derived are simplified into approximate closed-form equations using three idealized corrosion shapes, namely, constant-depth, elliptical, and parabolic corrosions. Numerical examples indicate that the closed-form approximate solutions provide good comparison with the generalized solutions. The closed-form approximate solutions are subsequently compared to experimental results from full-size tests of pipes with different corrosion depth and width. Parameter study conducted indicates that the shape of the corrosion defect has significant influence on the bending capacity of the corroded pipes. It is further pointed out that the idealization of the corrosion geometry by constant-depth, as commonly assumed in current code related to corroded pipes, will inevitably underestimate the bending capacity of the pipe, especially for the case of deep corrosion defect.更多还原