Design and Fabrication Concepts of Steel Liners for the Rehabilitation of Large-Diameter Pressure Pipelines

Steel liners for rehabilitation of existing large-diameter pipelines with rigid-wall construction have been used since the 1980’s and more recently for rehabilitation and upgrading the pressure capacity of existing steel pipelines with flexible wall-construction. The steel liners are installed, in lengths compatible with the host pipe’s lengths and joined with single lap-welded joints, using procedures similar to tunnel steel-liners. The annular space between the host pipe and the steel liner is filled with cement mortar by either pressure grouting from inside through grout ports or from outside using the slickline (steel tubing) method in the annular space. The steel liners are designed, in most applications, for internal pressure with a minimum wall thicknesses to accommodate handling and installation loads including back grout pressure. The steel liner cylinders are fabricated as either complete (full circle) cylinders with a diameter of approximately 150-mm (6-inch) less than the host pipe diameter or collapsible folded-and-strapped cylinders (cylinders are rolled but the longitudinal seam is left un-welded to fold the cylinder and reduce the diameter for ease of installation) with a diameter, after spring back, of approximately 75-mm (3-inch) less than the host pipe diameter. Complete description and fabrication methods of the tunnel liners and advantages and disadvantages of both types of steel liners will be provided. There are no standard procedures for the design of the steel liners for rehabilitation projects and it is usually left up to the owners and its consultants to check the steel-liner designs based on assumed design-condition scenarios. All design concepts assume that the host pipe will be completely deteriorated and will not contribute to the structural performance of the steel liner; The design checks performed for a 1800-mm (72-inch) diameter steel liner with field single lap-welded joints for the rehabilitation of 30 km (19 miles) of 1950-mm (78-inch) diameter prestressed concrete cylinder pipe (PCCP), with rigid-wall construction, design/build project will be presented; fabrication and testing procedures of the cylinders and the lap-welded joint design will also be discussed. The recent use of steel liners to rehabilitate or upgrade the pressure capacity of existing steel pipelines will also be discussed. Recommendations for additional design provisions for the steel liners for rehabilitation will be given.