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Calculation of allowable suspension span length for direct laying pipeline in shallow water area based on bending moment correction method

DOI：10.7511/jslx20221114003

 作者 单位 E-mail 付长静 重庆交通大学 水利水运工程教育部重点实验室, 重庆 400074南京水利科学研究院 水利部水库大坝安全重点实验室, 南京 210029南京水利科学研究院 港口航道泥沙工程交通行业重点实验室, 南京 210029河海大学 地球科学与工程学院, 南京 210098 王锦国 河海大学 地球科学与工程学院, 南京 210098 赵天龙 重庆交通大学 水利水运工程教育部重点实验室, 重庆 400074南京水利科学研究院 水利部水库大坝安全重点实验室, 南京 210029 ztl1986@163.com

海底管道悬空问题是管道工程建设中经常遇到的重要问题,当管道的悬跨长度达到一定值时,管道较容易失稳,而悬空油气管道失稳破坏导致的后果往往非常严重,因此需要对悬空的海底管道进行定期的维护和处理,但由于海上作业难度大,针对悬空管道的治理成本非常高,因此可考虑对处于悬空但在安全允许悬空范围内的管道暂时不进行加固,此时就需要计算管道的允许悬跨长度,为管道的治理提供依据。由于我国油田大多建设在近海地区,因此在考虑管道的悬空问题时需考虑浅水区波浪的特点。本文考虑浅水区波浪的非线性影响,推导得到浅水区波浪场内任意一水质点的水平流速和竖向流速计算公式,并根据该公式和Morison方程,进一步建立了管道悬跨水动力载荷的表达式,最后基于弯矩修正法,提出浅水区平铺海底管道允许悬跨长度计算公式。根据工程实例,结合本文研究,计算得到该工程所在海区平铺管道允许悬跨长度。

Suspended submarine pipelines are a common type of configuration in pipeline engineering construction.When the suspended span length of such a pipeline reaches a certain value,the pipeline is more prone to instability,and the consequences of the instability such as damage of suspended oil and gas pipelines are often very serious.Therefore,it is necessary to carry out regular maintenance and treatment of suspended submarine pipelines.However,due to the high cost and difficulty of offshore construction operations,it is necessary to temporarily not reinforce the suspended pipelines within the scope of safe suspension,which can greatly save construction costs.Therefore,it is necessary to calculate the allowable span length of the pipeline to provide a basis for the management of the pipeline.Since most of China’s oilfields are located in offshore areas,the characteristics of waves in shallow water areas should be considered when considering the problem of pipeline suspension.In this paper,considering the nonlinear effect of waves in shallow water,the calculation formulas of horizontal and vertical flow velocity at any water point in the wave field in shallow water are derived,and according to these formulas and Morison equation,the expression of the hydrodynamic load of the overhang of the pipeline is further established.Finally,based on the bending moment correction method,the calculation formula of the allowable span length of the submarine pipeline in shallow water area is proposed.According to the research results of this paper and the subsea pipeline engineering of an oilfield in Bohai Bay,the allowable span length of the pipeline is calculated.