Abstract
Flexible risers are an important component of offshore production systems of oil and gas. They are used to link subsea pipelines to floating installations, such as FPSOs. Flexible risers have been one of the preferred deepwater riser solutions in many regions of the world due to their good dynamic behavior and reliability.
Flexible risers are multi-layered pipes typically comprising of an inner flexible metal carcass surrounded by polymer layers and spiral wound steel layers, also referred to as armor wires. The most common integrity issues relating to flexible risers are mechanical damage to the outer sheath or a venting system's failure. These can lead to a pressure breach of the out sheath and flooding of the riser annulus, ultimately weakening the riser integrity through corrosion of the internal wire. This paper discusses the motivation and business driver for developing and implementing new and cost-effective flexible risers' inspection methodologies based on a multi-technology approach that allows the assessment of the flooding status of the riser and the corrosion status of the internal steel layers. The paper is based upon worldwide flexible risers' inspection campaigns. The complex multi-layered structure which characterizes the flexible risers is not favorable for inspection with most non-destructive testing (NDT) techniques, which makes structural integrity evaluation difficult. Initial industry efforts concentrated on the search for a single technique which would ensure reliable detection of armor failure, but recent experiences have shown that the safest approach may be to take advantage of a Multi-Technology Approach obtained when different instruments are combined. Backbone of the new multi-technology approach presented is the use of a MEC (Magnetic Eddy Current) based subsea crawler that has the key advantage to rapidly scan large surfaces with or without coating and detect reliably internal wire defects. MEC is complemented by a frequency-based ultrasonic measurements system to assess the flooding status of the riser. For the assessment of specific issues, a CT (Computed Tomography) scanner is used to support the inspection. The inspection data are processed in real time for an immediate assessment of the integrity of the asset. The crawler is equipped also with an advanced cleaning and high-definition video system. Examples are presented, and comparison is made between traditional and new inspection methodologies based on recent flexible risers' inspection campaigns to demonstrate the improvement of inspection effectiveness and efficiency.
