Mechanically Lined Pipe: Installation by Reel-Lay

Abstract

Abstract A cost effective solution for the transportation of corrosive fluids wasconsidered as the combination of mechanically lined pipe (Lined Pipe) installedby the reel-lay technique. Mechanically bonded bimetal pipe has beensuccessfully used in towed pipeline bundle projects by Subsea 7 over many yearsand has been demonstrated to be a viable cost-effective alternative to moreexpensive options such as solid corrosion resistant alloys (CRA) ormetallurgically clad pipe. The work presented in the present paper was undertaken to demonstrate to theindustry the feasibility and the significant advantages of being able toinstall mechanically lined pipe by the reel-lay method. Test strings were manufactured and subjected to a conservative full scalereeling simulation program. Accurate metrology of the carbon steel carrier pipeand CRA liner surfaces was performed at different stages of manufacture andsimulated installation, including prior to and after full scale plasticdeformation. High frequency resonance fatigue testing was carried-out to assessthe post-reeled endurance of the joint for SCR application. Material andcorrosion testing were done and finite element analysis (FEA) was performed inorder to understand the effect of internal pressure during installation and itscapacity to prevent wrinkle formation. A total of 9 test strings were used as part of the development program and ithas been demonstrated that, for high quality lined pipe, the proposedmethodology and procedures, which utlise internal pressure, permit the pipe tobe installed on the seabed fully fit-for-purpose with no formation of anywrinkles. Also it has been possible to demonstrate that the liner behavior aspredicted by the FEA showed good correlation with the observations made duringthe full scale reeling simulation. Finally the tested pipes met the targetfatigue life requirements. The work was performed in compliance with DNV recommended practice for newtechnology qualification RP-A203 (DNV-RP-A203, 2001) and awarded the" fit-for-service" status. Introduction The continued exploration and production of subsea developments and longdistance tiebacks worldwide will demand from the industry to design more of itssubsea infrastructures and pipelines to cope with increasing amounts ofcorrosive medium throughout the life of field. The material selection process to satisfy such demand often influences thepipeline design towards the adoption of CRA materials. These are mainlymartensitic stainless steels (e.g. 13%Cr), austenitic stainless steels (e.g.316L), Duplex stainless steels (e.g. 22%Cr, 25%Cr) or nickel alloys (e.g. Alloy825, Alloy 625). Due essentially to their specific chemical compositions butalso their manufacturing processes, these materials are generally moreexpensive than the commonly used carbon manganese steel. In order to reduce theoverall material cost, an option is to use them in the form of a mechanicallylined pipe. The CRA material is thus used only for its corrosion resistance inthe form of a thin liner pipe mechanically assembled within a carbon steelouter pipe. The carbon steel contribution, in this case, is solely to providethe required mechanical strength to the finished pipe. Several manufacturingroutes exist to produce this type of pipe, however, the current developmentprogram was specifically carried-out using high quality mechanically lined pipemanufactured by the hydraulic expansion process.