Calculation of maximum allowable free span length and safety assessment of the DF1-1 submarine pipeline |
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Authors: | Jishang Xu Guangxue Li Juan J Horrillo Rongmin Yang Lihua Cao |
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Institution: | 1. College of Marine Geo-sciences, Ocean University of China, Qingdao 266100, P. R. China; Key Laboratory of Submarine Sciences and Exploration Technology, the Ministry of Education of China, Qingdao 266 2. Department of Maritime Systems Engineering, Texas A &M University at Galveston, Galveston, TX 77554, USA. |
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Abstract: | The DF1-1 submarine pipeline was investigated using a dual-frequency side-scan sonar and a swath sounder system. More than
a hundred scour pits under the pipeline were found, most of which have caused the span of the pipeline to increase and threatened
its safety. The maximum allowable free span length (MAFSL) of the pipeline was determined through the limitations regarding
maximum allowable stress under static or quasi-static loads and the onset of Vortex Induced Vibrations (VIV) under different
hydrodynamic actions. The results show that the MAFSL under static conditions is 56 m. However, the MAFSLs are 30 m and 20
m under ordinary weather conditions and hurricane-induced currents for the 100-year return period, respectively, to avoid
VIV as calculated by using the highest safety class factor. It is suggested that spanning pipelines longer than 20 m should
be supported. Additionally, eight successive spans which may also threaten the pipeline were proposed. The most hazardous
scour pits are along the pipeline section from KP42 to KP51. |
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Keywords: | submarine pipeline scour span safety assessment Vortex Induced Vibrations (VIV) maximum allowable span length |
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