Hydraulic expansion of lined pipe for offshore pipeline applications

Carbon steel pipe lined with a thin layer of a corrosion resistant alloy is an economical product used in offshore pipelines that carry corrosive hydrocarbons. The liner and carrier pipe are mechanically expanded together so that on unloading they end up in interference contact. The contact pressure that develops is essential for keeping the composite pipeline intact under bending and axial loads experienced during offshore installation and operation. The manufacture of lined pipe by hydraulic expansion is analyzed with a custom model, which is used to establish the effect of various geometric, material, and manufacturing parameters on the contact pressure. The analysis incorporates incremental plasticity that accounts for material hardening and the biaxial states of stress that develop. It is demonstrated that plastification of the carrier pipe is beneficial, and that a relatively low yield stress liner with low hardening, coupled with a high yield stress high hardening carrier pipe increases the contact pressure. The analysis presented and the results should prove to be useful in the design of the manufacturing process of lined pipe aimed for offshore applications.