In 2017, after a failure of a flexible riser operating in an environment with high level of CO2, a new failure mode of the flexible pipes was reported: Stress Corrosion Cracking induced by CO2(SCC-CO2). This issue was not considered in the design and manufacturing standards of these equipment. In this context, this paper covers a literature of SCC-CO2 phenomenon. Moreover, the impacts on the flexible pipes due to this failure mode are discussed. Lastly, this research focuses on the current technologies and tools used to inspect and access the integrity of the pipes used on gas injection and production lines. The paper is written based on detailed review of the literature. A set of relevant keywords were used on peer-reviewed journal articles and conference papers mainly available in the OnePetro database. Some recognized books, technical specifications and PhD thesis were also consulted. The papers included in this literature review were selected based on four steps: identification, screening, eligibility and inclusion (Moher et al., 2009). This methodology allowed to find out what is the current state of the art about the topics covered in this study. This detailed review of literature revealed that after the issue reported in 2017, the industry invested in the research of the SCC-CO2 phenomenon. Many studies were conducted in order to investigate what are the main factors that triggers this failure mode on the flexible pipes used for the production and gas injection in the deep-water and ultra-deep-water fields with high levels of contaminants and harsh metaocean conditions. Then, different technologies and tools were developed to inspect the flexible pipes. Operators can use this data to estimate the remaining service life of the lines. There are proven tools that can inspect the gas injection pipes using different non-destructive techniques. However, there is still a gap on the inspections of the annular region of the production flexible pipes. This happens due to the limitation of reading through the thermal insulation layer contained on them. This is very critical because the inspection of the pipe annulus detects if it is dry or flooded. This information is vital to assess the integrity of the structural armors of the flexible pipes.

Flexible pipe systems are extensively used in the oil and gas offshore production segment due to its ease of transport and installation, design versatility and performance, especially in deep and ultra-deepwater fields. The criticality of the system and the difficulty of having an accurate lifetime prediction using current inspection tools require the flexible pipe design to have a very high safety factor, which may lead to overdesign and/or uncertainty on the actual damage state of a pipe in operation. The annular environment condition of flexible pipes has a big impact on the consumption of its operational life due to seawater ingress or bore fluid gas permeation. In order to better understand and mitigate the associated failure mechanisms we developed, built, and commissioned PipeACOM, the Flexible Pipe Annular Control Manifold, with the objective of connecting the annular regions of adjacent flexible pipes, control its flow and monitor the annular environment throughout the life of the flexible pipe system. In this paper we describe the main features of the PipeACOM system, present the setup and experimental results of the validation tests performed in a prototype system installed in a production flowline at the Brazilian pre-salt fields at over 2300 meters of water depth, reaching the Technology Readiness Level of 6 based on API RP 17N criteria and earning the 2020 National Technology Innovation award by the Brazilian National Petroleum Agency (ANP).

Flexible pipes annulus condition is a key concern regarding the pipe's integrity. The presence of water in the annulus may lead to a corrosive environment which reduces the fatigue life of the tensile armours. Annulus flooding is the most frequent failure case [1] and may occur due to a failure on the external sheath, failure of the end fitting sealings or failure of the vent valves installed in the end fittings. Water may also reach the annulus not from the outside but as condensation of the permeated gases from the bore. One of the current approaches to assess the annulus condition consists in the detection of annulus flooding through free volume measurment by means of a positive pressure test or a vacuum test. This intervention may be complemented by gas sampling from the annulus and measurement of bore-to-annulus gas flow permeation rates. Conventional venting systems on the top end fitting typically do not allow for these operations but for approximations of permeation flow rate by monitoring of annulus pressure build-up because of pressure sensors installed in the venting system. To address flexible pipes integrity, the Mobile Annulus Testing System (MATS) was developed. MATS allows for the determination of free annulus measurement, by means of conventional positive pressure or vacuum testing. Moreover, MATS allows for permeation gas flow rate measurement and gas sampling. Also, MATS is easily deployable and can be transported as cargo on flight helicopters. MATS was tested on a field campaign in 09 flexible risers in the Tupi Field in Santos Basin, brazilian pré-salt, and this paper presents the results obtained.

This paper describes innovative methodologies in industrial lab-scale, named LAB-TWIN, developed within a joint industry project (JIP) for flexible pipes integrity assessment under harsh environments, focused on CO2 induced failure phenomenon (SCC CO2). The LAB-TWIN comprises applying specific conditions according to the pipe application – e.g., production oil (PO), gas injection (GI) – to assess gas permeation through the pipes and explore the SCC CO2 degradation mechanism in a controlled environment, from initiation until failure. To reproduce, as closely as possible, the operational field conditions, the experiments were designed to allow the application of specific boundary conditions in flexible pipe sections, including chemical content in the pipe bore (such as gas mixtures and oil), internal and external pressure and temperature, and axial static loads. The flexible pipe samples were assembled with customized test end-fittings that provide privileged annulus access, allowing the monitoring and measuring of annulus conditions throughout the tests. The samples were submitted to a corrosion process called degradation. After this period (months or even years), each pipe sample is dissected and inspected. Then, the materials are assessed at the laboratory level to determine the environmental impact in their main mechanical properties. During the experiments, the gas permeation phenomenon through the polymeric layers occurs. It allows the generation of experimental data that can be used to calibrate theoretical permeation models based on annular pressure building up and annulus environment content, such as CO2. The LAB-TWIN delivers valuable data to support permeation methodologies, better understand the SCC CO2 phenomena, and the up-to-date assessment of the flexible pipes service life prediction.

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