Subsea Connectors Designed for Repair of Corrosion-Resistant-Alloy-Clad Pipelines

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 221852, “Repairing Corrosion-Resistant-Alloy-Clad Pipelines: The Weld or Connect Choice, ” by Francesco Cavallini and Enrico Girello, Saipem. The paper has not been peer reviewed. _ The use of subsea corrosion-resistant-alloy (CRA) -clad pipelines is increasing, and plans exist to expand their use in developing large reservoirs and transporting high-pressure, high-temperature, highly corrosive fluids. The complete paper compares traditional welding techniques, such as above-water repair methods and underwater hyperbaric welding, with novel options offered by subsea connectors purposely developed for CRA-clad pipelines. These connector solutions ensure continuity of containment of corrosive fluid by means of engineered nonelastomeric metallic seals. Grip and Metal Seal Connector (GMSC) System Description. The presented novel repair connector is a mechanical connection system to be fitted onto the pipeline cut end, which is to be prepared in advance. Key features include the following: - Permanent repair by means of a metallic sealing technology - Allowance of full piggability of the pipeline after the intervention by not restricting the pipeline inner diameter (ID) - Restoration of original operational functionality of the pipeline - Allowance of diverless permanent repair intervention - Confirmation of correct installation by backseal testing - Design life of 30 years - Maximum design pressure of pipeline of 360 barg (extendable) - Maximum water depth of pipeline of 2000 m (extendable) The GMSC is composed of a body with grip and seal elements and a flange or hub welded to the main body. The mechanical connection with the pipe is achieved by gripping wedges and teeth, while a front metal seal ensures sealing at the pipe cut end. Both functions are activated by a system made of tensioned rods and hydraulic wrenches or tensioners. A pipe-end support mechanism allows constraint of pipe-end radial displacements caused by pressure or load changes. The front metal seal allows use of the connector for sweet and mild sour-service applications and for more-aggressive sour-service conditions. The seal is pushed against the pipe end to ensure a metal-to-metal contact. The sealing system is designed to allow recovery of possible angular errors between the connector and the pipe-end face caused by subsea cutting or machining and installation operations. The GMSC surfaces exposed to seawater will be protected by a combination of suitable coatings and cathodic protection anodes. The main connector components are illustrated in Fig 1. The GMSC is designed to be installed and operated by remotely operated vehicles (ROVs) or divers. In principle, the repair connector is reversible because no permanent deformations of components or locking mechanisms exist that prevent restoring the initial positions of the system. The GMSC reinstates the pipeline’s original internal containment of the corrosive fluid by providing internal continuity to the noble material without any ID reduction.