Flexible Pipes were widely used in Brazil offshore developments and the challenge on overcoming increasing water depths, high pressures and fluids with high contaminants was always present. In 2017 a new failure mode, called SCC CO2 was disclosed bringing such disruption in the use of this equipment since, at that time, the conditions observed in Brazilian Pre salt were like the "perfect storm" for the failure mode to happen. It had high concentrations of CO2, therefore high permeation in the anulus, high stresses and the possibility to have anulus flooded as result of an outer sheath breach or even due to permeated water. These were the triple conditions needed to have the failure, considering that all metallic material used in the pipe were subjected to this phenomenon. Since the discovery was made, several test campaigns to better understand and replicate the phenomena started. They covered pipe retrieved from field dissection, several small-scale materials testing, and fracture mechanics to create reliable crack propagation calculations. There were 3 mains focus areas; to understand how to deal with the installed fleet, to define the conditions in which a crack would appear and define, using fracture mechanics, how long a crack would take to break the wire. In other words, it was intended to define what is the remaining service life. As a result of this investigation some initial beliefs like that all materials were subjected to the phenomena and that a solution was far away were somehow reduced and reshaped. There was also the initiative to embark on technology for detection of the anulus condition, mainly to define if it is flooded or not. Some ROV inspection means were added to the endfitting and some sensors were added to the interconnected pipe sections that allow conditioning monitoring or inspection from the floating unit, not using a ROV. This paper will cover the improvements done since the disclosure of the phenomena in 2017, reviewing what is known about it so far, what is still to be discovered and how the results achieved to date can contribute for a more reliable and longer service life for the flexible pipes to be applied in a rich CO2 environment.
The development of Brazil’s Offshore fields has been performed using flexible pipes because this pipe technology offers significantly increased flexibility, enabling the movement of pipes between wells and reducing lead time to bring a well onstream as compared to rigid pipe solutions. In addition, the decision of where exactly to drill development wells can be delayed, thus making the drilling campaigns easier, cheaper and faster [1]. With the increased activity in Pre-Salt, some challenges to flexible pipes were uncovered and needed to be addressed, notably oil composition and corrosive agents, e.g. H2S, and, specifically for the case of this paper, CO2. At high pressures, such as found in pre-Salt fields, these contaminants create new Stress Corrosion Cracking (SCC) failure modes and several mitigation measures have been adopted to overcome them, focused either on the installed fleet or on the next generation of pipes to be delivered. SCC is a condition that induces failure in the pipes’ metallic layers, but it needs three elements to occur: water, tensile stress exceeding a critical level and a susceptible material. If one of these three elements is suppressed, the phenomena does not to happen. This paper will cover and present a technology developed to detect the annulus water condition — dry or flooded — and thereby allow a correct integrity management strategy to be adopted. The technology is based on an embedded sensing system together with topside equipment to read the status. The use of such a system is important for the next generation of flexible pipes as it will allow better management of the fleet, with the required measurements performed from the production unit without the need of any support vessel and hence at a reduced cost.
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