Wrinkling and Collapse of Girth-Welded Lined Pipe Under Bending

Pipelines and flowlines that carry corrosive hydrocarbons are often protected by lining them internally with a thin layer of a corrosion resistant material. In the most economic method, the liner is brought in contact with a carbon steel carrier pipe by mechanical expansion. In applications involving severe plastic bending, such as reeling, such a liner can wrinkle and collapse while the carrier pipe remains intact. A numerical framework for establishing the extent to which lined pipe can be bent before liner collapse was presented in [1,2]. This framework, suitably extended is used here to examine the effect of girth welds on liner collapse. The modeling starts by simulating the expansion process that plastically deforms the two tubes bringing them into contact. Bending plastically the composite structure leads to differential ovalization of the two tubes and detachment of the liner. The girth weld locally prevents this detachment creating a periodic boundary effect in the liner. With increasing bending this local disturbance grows leading eventually to a diamond-shaped liner collapse mode. The problem is first investigated using a 12-inch carrier pipe base case followed by a parametric study of the factors that influence collapse.