Abstract
There is limited data on the performance of coatings, materials and cathodic protection systems installed subsea1, 2. Most systems remain submerged for their useful life and are often abandoned on the seabed. The recovery of the hardware provided an opportunity to autopsy the hardware for the purposes of validating cathodic protection designs and coating systems; specifically coating performance, anode consumption, and internal wall thickness allowances.
There were four types of coating on the hardware: Two-part epoxy paint, fusion bonded epoxy pipe coating, heat shrink sleeve field joint coating and thin film fluorocarbon coating for friction reduction. Apart from some higher interfacial porosity, the fusion bonded epoxy coating was comparable to new coating. The paint coating exhibited poor adhesion and blistering in some areas but was well bonded in others. The heat shrink sleeve was in good condition with no signs of water ingress to the weld between the sled piping and flowline. Although adhesion of the thin film fluorocarbon coating was good, it exhibited advanced signs of breakdown with a number of small blisters.
Using data developed by Shell Exploration and Production Company for cathodic protection and the simple “yoke” structure on the hardware, a coating breakdown factor of 5.4% was calculated. This is lower than the as-designed case of 10.4%.
Cathodic protection design for hardware is part of a corrosion protection system which should be addressed during component design and fabrication. The verification of electrical continuity is an important step in the fabrication of the equipment that has implications on the corrosion protection and integrity of the equipment.
