Development of a Post-Installed Deepwater Monitoring System

Abstract

A monitoring system that can be deployed on already existing deepwater risers and flowlines has been developed. This paper describes the design concepts and testing that was performed in developing the monitoring system. A major challenge of a post-installed instrumentation system is to ensure adequate coupling is achieved between the instruments and the riser or flowline. This work investigates the sensor coupling for pipelines that are suspended in both the water column (from topside platform to the seabed) and for those that are located directly on the seabed. These different environments necessitate two sensor attachment methods: (1) sensor clamp design with subsea adhesive and (2) sensor clamp design with friction surface coating. This paper addresses the adhesive attachment method. The monitoring elements consist of fiber optic sensors that are encased in a polyurethane clamp. With a subsea adhesive, the clamp can be installed by divers in shallow depths or by use of an ROV for deeper applications. The NASA Johnson Space Center was initially involved in the selection and testing of subsea adhesives. It was determined that up to 75 percent of the bonding strength could be achieved with the adhesive from optimal dry bonding versus bonding in submerged sea water environments. The next phase of the study involved the design, fabrication, and testing of several prototype clamps that incorporated the fiber optic sensors. Several molds were produced by NASA using 3-D printing that allowed the fabrication of subscale test articles that would accommodate 4-inch and 8-inch diameter pipes. The clamps were installed with adhesive in a "wet" environment on the pipe test articles and evaluated in the NASA Structures Test Laboratory. The tension/compression and bending tests showed that the prototype sensor clamps achieved good coupling, and could provide high quality strain measurement for active monitoring.