Most hydrocarbon pipelines installed recently in the Middle East operate at relatively high pressures and temperatures: maximum inlet operating temperatures >90°C and pressures >135 barg. These pipelines are susceptible to Euler buckling from high axial compressive force induced in the pipeline by the temperature and pressure. Any uncontrolled lateral buckling is a potential hazard for a pipeline’s structural integrity, especially when all compressive force is released at one point and excessive feed-in occurs.
Possible mitigation measures include lateral restraint by rock dumping or trenching, or midline spools. Another possibility is to induce the pipeline to buckle in a controlled manner, perhaps at several locations, rather than allowing it to suffer an uncontrolled, large buckle at one location only. This is known as buckle initiation. “Snake-lay” and “Vertical Imperfection” are two methods that have been implemented successfully to initiate controlled buckling. “Buoyancy” is another method, but is yet to be implemented.
Snake-lay is a relatively reliable solution but, depending on pipe-soil interaction, sometimes requires a very short radius to initiate the buckle. Installing large diameter pipelines with short radii may invite other problems such as pipeline instability during laying, or may require additional counteracting measures to maintain the specified lay radius. The lay radius can be increased with additional sleepers at the crown of the snake-lay, with a well-defined low friction factor between the pipeline and the support.
This paper discusses the behavior of snake-lay pipeline with and without vertical sleeper supports at the crown of the pipeline, and demonstrates what effects supporting the pipeline at the crown will have on the buckling mechanism and the pipeline integrity.