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H-Lay Analysis Feasibility Case Study

H-Lay Analysis Feasibility Case Study

Benefits
Atteris conducted a feasibility study to evaluate the feasibility of a H-lay concept for a range of pipe sizes, water depths and sea-states. The concept could present a cost-effective pipelay solution to the Client and also to Australian market.
Background
ARV is developing a hybrid pipelay concept with a view to provide cost-effective pipelay services for small diameter rigid pipelines in the Australian market. The concept consists of an adjustable J-Lay tower which can lay pipe over a range of exit angles essentially between 0 and 90 degrees. Atteris has been engaged by ARV to perform pipelay analysis to assess the likely operating range of the system.
Work Performed by Atteris

Atteris conducted both static and dynamic pipelay analyses over a range of pipe sizes (6-in to 12-in), water depths (7 m to 250 m) and sea states (up to 2 m Hs) to evaluate the feasibility of the proposed H-lay concept. The analyses considered a 3-hour irregular sea state (simulated using JONSWAP) and was performed to cover the period when the most severe sea elevation occurs. For each load case analysed, the maximum von Mises stress, angle of departure and difference in arc length to layback distance were recorded.

Atteris also performed sensitivity analyses to study the effects of increased clamp tension, reduced wall thickness and different peak wave periods on the results. From the analyses, it was concluded that the proposed H-lay concept is suitable within the parameters analysed. It was apparent from the analyses that a key issue in ensuring the integrity of the pipeline during lay is control of the stresses at clamp locations. Atteris made recommendations that would reduce the localised stress at the clamp location i.e. releasing the pitch restraints on the clamp and introducing a pipe support that could improve peak pipe stresses. However, it was also noted that operational constraints may prove to be the limiting factor rather than pipe stresses considering the range of motion of the clamped pipe end.

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