Analytical Model for Mechanically Lined Pipe Hydroforming

Mechanically Lined Pipe (MLP) contributes to a cost-effective solution to long-distance transportation of oil and gas carrying corrosive substances. Causticity isolation is attained by lining a thin layer of Corrosion Resistant Alloy (CRA) upon the inner wall of carrier pipe. The interlayer mechanical bonding is crucial and typically achieved by expanding liner and carrier pipe simultaneously. Insufficient residual contact pressure makes thin-walled liner vulnerable to detachment when subjected to excessive compression or curvature. After experiencing repeated plastic bending, such as reel-lay installation, detachment can evolve into liner buckling and collapse inside the carrier pipe, and ultimately damaging the structure. Thus, the MLP hydroforming is mathematically modeled. By decomposing the expansion stages of each component, a comprehensive analytical framework is developed for full-process analysis of MLP manufacturing, encompassing single cylinder pure elastic, partially plastic, post-yield expansions (w/o and w/ external contact). The analytical framework employs von Mises yield criterion, Hencky deformation theory, and the auxiliary variable method to conduct stress-strain analysis. Its capacity to incorporate initial gap dimension, strain-hardening and partial plastification in mechanical bonding prediction is validated through Finite Difference Method (FDM). The proposed model provides an explicit equation system that is easily implementable for onsite MLP hydroforming fabrication.