Mechanically lined pipe is a cost-effective pipeline solution when corrosion protection is required against production fluids. Under successive bending - e.g. during the reel-lay process - the liner can collapse from the outer pipe, thus ruining the pipeline.
Assessment of such failure mode is performed using Finite Element Analysis (FEA). The analyses consider nonlinear phenomena including the interaction between the liner and the backing steel, but are time-consuming.
This can be improved using design space description and exploration combined with statistical regression techniques. This paper presents the implementation of such methodology and the results are discussed.
Several solutions are commonly used to protect flowlines from corrosive hydrocarbons including the use of corrosion inhibitors, plastic liners, corrosion allowance, solid corrosion resistant alloys and double walled pipe which contains cost-effective mechanically bonded lined pipe (MLP) (Kyriakides & Corona 2007). MLP is made of a host carbon steel pipe, called "Backing Steel" lined internally with a stainless seam-welded pipe, called "Liner".
During assembly, the backing steel & liner pipes are formed separately, and one is pulled into the other. This may include heating the backing steel and cooling the liner as described in Focke's thesis (2007). The liner is then subjected to a controlled expansion operation, during which the liner comes in close contact with the backing steel. The expansion is in displacement controlled mode to control the expansion of the backing steel pipe. As the liner has expanded plastically, the liner diameter is greater than its initial state. This process leaves residual hoop stresses on both liner and backing steel pipe, as shown - for instance - in Yuan and Kyriakides study (2014).
Once delivered, MLP joints are assembled into long stalks (typically 500 to 1000 m) for spooling. The pipe is plastically bent onto the reel. The tail end of the pipe is kept under back tension during spooling, thus holding the pipeline tight on the reel drum at a constant tension until deployment. Spooling-off takes place as the vessel lays the pipeline on the seabed. The pipe is unreeled under tension causing reverse bending in the suspended catenary before it passes over the vessel aligner. It is then plastically deformed again, in the same orientation as the reel. The pipe then passes through the vessel straightener which applies a reverse curvature, so that the final straightness of the pipe reaches tolerable limits.
