Liner buckling during reeling of lined pipe

Abstract

An effective way of protecting offshore lines that carry corrosive hydrocarbons, is by mechanically lining carbon steel pipes with a thin layer of corrosion resistant alloy. A disadvantage of this product, is that when bent to curvatures such as those experienced during reeling the liner can buckle. The sensitivity of this instability to the main problem parameters was previously studied under pure bending. In the present study the problem is examined under the more complex loading experienced as it is wound onto a reel while under some back tension. A large-scale custom numerical model of the winding process of a previously expanded lined pipe is presented capable of dealing with the geometric, material and contact nonlinearities of the problem. The model is used to establish the deformation history experienced by the carrier and liner pipes during winding, the causes of liner instability, and its sensitivity to the main problem parameters. During reeling, a transition length a few diameters long bends to an increasingly larger curvature until it comes into contact with the reel. Back tension controls the length and curvature of this transition zone safeguarding the line against local buckling. Modest levels of tension are shown to also delay the onset of liner wrinkling. The more complex loading history experienced by the lined pipe as it approaches the reel changes the prevalent buckling mode but its sensitivity to initial geometric imperfections reported under pure bending remains. The liner instability becomes more prevalent as the diameter increases but at the same time smaller diameter lines could be reelable. The recent trend of winding lined pipes under small levels of internal pressure is confirmed to be an effective means of avoiding liner instability.