Polymer lined water injection pipelines have proven to be a cost effective alternative solution to corrosion resistant alloy clad pipelines for subsea applications. At normal operating conditions these pipelines are often considered to be at low risk from internal corrosion. This is because a polymer liner, if intact, provides the main barrier to mitigate against the internal corrosion mechanisms, which include oxygen corrosion, MIC, and CO2 corrosion if produced water is present.
This paper presents a case study based on the experience from a North Sea asset, where polymer liner at two spot locations was damaged due to the remedial works, exposing the carbon steel to general and localised corrosion. The first part of the paper gives history of anomaly identification and details of the UT inspections, which involved using an ROV deployed bespoke inspection tool. The inspections enabled information on the condition of the pipes at the locations where the liner was damaged, and allowed estimation of a corrosion rate (up to 1.95 mm/year). The second part of the paper summarises the corrosion defect assessment, undertaken using the WGK in-house software IC Finesse. The assessment was required to confirm that the pipelines with anomalies were fit for continued service, and enabled estimation of the remaining service life.