AN ANALYSIS OF THE STRESSES INCURRED IN PIPE DURING LAYING OPERATIONS

It is common practice during the construction of underground pipelines that pipe sections are welded together at Surface level and then lowered into a pre-dug trench. Lowering of the pipeline into the trench incurs bending and/or torsional stresses that are not typically considered during the design of the pipeline. Current Industry guidelines recommend the pipelines be lowered into the trenches with care in order to avoid cracking of the pipe, or yielding that could lead to residual stresses and distortion. There are currently no formal guidelines oil how to minimize these stresses, or estimates of the magnitude of stresses associated with these operations. The stresses incurred during the laying of pipe can be estimated using simple beam bending and torsion equations. One can simplify the analysis by assuming the pipeline is either a cantilever with a given load or deflection at one end, or, a beam with given loads, deflections and rotations at both ends. The choice of boundary conditions influences the calculated stresses, and can be considered appropriate for different pipe laying operations. If a pipeline is moved laterally during the laying operations one must consider the associated torsional stresses. The combination of bending and torsional stresses will lead to different stress states on different sides of the pipe, sonic of which may result in cracking or yielding. The goal of this work is to develop a framework for estimating the stresses Incurred in pipe during laying operations, as a function of pipe length, deflection, diameter and wall thickness. This will allow guidelines to be developed that will allow construction crews to ensure that pipelines are laid with minimal damage. A variety of analyses has been considered during the Course of this work and is presented in this paper. It is expected that discussion of these analyses with industry representatives will lead to improved construction protocols.