Abstract: This invention is a method for joining sections of in-situ cement-mortar lined pipes adapted for high pressure water injection service. The method utilizes a backing ring with one beveled end inserted into a beveled end of the first pipe section and the other beveled end of the backing ring projecting from the first section and adapted to mate with a beveled end of the second pipe section. The pipe sections are then cement-mortar lined. The ends of the linings are then cut back and beveled to facilitate alignment and fit-up, and to provide a cavity and anchor for the retention of a heat expanding grout that is applied to both ends of the lined mating pipe sections to seal the joint. A root opening is left between the mated ends to permit weld penetration and fusion of the butted ends of the steel pipe and a space for the excess and expanding grout to protrude internally.