Anomaly Criteria for General Visual Inspection of Subsea Flexible Pipes

Abstract

Abstract For flexible pipes in subsea applications, General Visual Inspection (GVI) by Remotely Operated Vehicles (ROV) remains the most common inspection method that is used on a routine basis. It enables verification of pipe configuration or layout and also helps to identify any areas of concern indicative of an increased risk of in-service failure. The success of ROV GVI chiefly relies on the anomaly criteria used, these help inspectors to identify any areas of concern, which can then be assessed by a competent person to ensure any threat to the integrity of an inspected component is identified and addressed. Currently there are no commonly accepted anomaly criteria for ROV GVI of flexible pipes. As a result there is no consistent approach between different operators and experience shows that the inspection approach and anomaly criteria are often adopted from what has traditionally been used for rigid pipes. Since flexible pipes have different design and associated failure threats and mechanisms to rigid pipe, use of this approach may result in under or over inspection of flexible pipes. This paper presents a set of anomaly criteria for ROV GVI of flexible pipes. The criteria were developed using the experience and lessons learned from a population of approximately 350 flexible pipes from two different manufactures operating in deep waters of the UKCS for over a period of 20 years. The criteria cover dynamic flexible risers and associated ancillary equipment, seabed flexible flowlines and jumpers. The applicability of the proposed anomaly criteria to other systems, the benefits of having commonly accepted anomaly criteria, the anomaly detection capability of ROV GVI and the reporting of anomalies are also discussed.