On the Laying of Pipelines in Deep Water

A rational procedure for the dimensioning of subsea pipelines is described. It consists of a computer program which determines pipe diameter and wall thickness for given quantities of flow rate, depth of water, bottom current velocity and towing capacity of the lay barge. Steel quality, out-of-roundnees of pipe and characteristics of the concrete coating are also taken into account. The paper explains in detail the bending/ buckling criteria used in determining the steel pipe wall thickness. An analytical expression is derived for the maximum combined stress of a pipe subjected to constant external pressure and an external bending moment, allowing for initial cut-of-roundness. The concrete coating dimensions are determined in such a way that sufficient negative buoyancy of the air-filled pipe in water is maintained to counteract the lift originating from bottom currents. The bending moment is calculated with the help of large-deflection beam theory, solving the non-linear differential equation by means of finite-beam-element techniques. Sample applications of the design technique are given and checked against model tests and full scale data.