A Stress Check Procedure for Pipe Lowering-In Process During Pipeline Construction

The quality of pipeline construction is determined by the effort of controlling the pipe stress level. Constraints may include various factors, such as pipe size, side boom lifting capacity, the number of side booms, side boom spacing and the lifting height profile. The use of girth weld flaw size limit established by Engineering Critical Assessment (ECA) for a given construction condition, makes the accuracy of pipe stress even more important. This is not only because stress level is one of the controlling parameters of the ECA results, but also because in some cases, such as low girth weld fracture toughness, stress level must be controlled with a very narrow window to keep a meaningful ECA that leads to a reasonable weld repair rate. An optimized pipe lifting height profile can be obtained from stress analysis using finite element method based on available construction equipment capabilities. From a practical perspective, an optimized pipe lowering-in plan may not be executable in the construction field. It is thus desired that a practical approach be provided that captures the key feature of construction practice and at the same time makes the key measures recordable. This paper provides a set of stress check equations derived using beam deformation theory. The calculation results using these equations show that for normal pipe lowering-in practice, pipe stress level can be effectively controlled by checking and controlling the lifting height of just one or two points. The approach proposed is to be used in conjunction with case specific finite element analysis.