The collapse strength of flexible pipes is a well known property and predicted by means of numerical or analytical modelling. However, recent oil field discoveries in the Brazilian pre-salt area, in water depths up to 2500m, are pushing the industry to evaluate the effects of flexible pipe curvature on its collapse resistance when the pipe is subjected to extreme levels of hydrostatic pressure such as that expected in the Brazilian pre-salt area. As part of Wellstream's R&D programme, a numerical model was specifically developed to predict flexible pipe collapse resistance when subjected to curvature to assess and quantify the effects of curvature on the flexible pipe collapse resistance. This paper summarizes the numerical modelling process and experimental calibration performed using five different pipe structures specifically designed for the pre-salt cluster. A total of 45 calibration tests were performed using samples taken from the same production run in order to eliminate variance in production machine setup and raw material batches. Regular production equipment, setups and quality control procedures were used to manufacture the test samples so that the collapse resistance of the pipes could be evaluated against conditions identical to commercial manufacturing. Of the five different pipe structures evaluated in this test programme, one of the pipe structures supplied for the TUPI EWT project development is already installed and operating at a water depth of 2140m. The test programme allowed the experimental assessment of the curvature effects on flexible pipe collapse behaviour, demonstrated the suitability of flexible pipe structures and model to predict the effects of curvature on collapse resistance.

Resumo: O Brasil é mundialmente renomado como um líder na extração de petróleo, em águas profundas e ultra profundas. Dentro da cadeia produtiva, grande parte do petróleo e do gás produzido é escoada através de dutos flexíveis que conectam os poços de produção às plataformas. Quando estão apoiadas no fundo do mar, em condição de serviço estático, os dutos flexíveis são denominados flowlines e quando se elevam do fundo do mar até a plataforma, em condição de serviço dinâmico, são denominados risers. Os tubos projetados para aplicações dinâmicas são dotados de bends stiffeners, componentes com formato cônico e, em geral, de base uretânica que têm a função de fornecer uma transição entre a estrutura dos tubos, de rigidez suave, e a plataforma, extremamente rígida. Este trabalho abordou a variação das propriedades mecânicas de poliuretanos como resultado da ação da hidrólise, por envelhecimento acelerado. Os corpos de prova foram expostos a 50, 60 e 70 °C. A variação de massa também foi determinada considerando que esses materiais são projetados para uma vida útil superior a vinte anos. Os poliuretanos apresentaram degradação significativa a 70 °C, o que pode reduzir seu tempo de aplicação no campo por falha mecânica quando submetido a elevadas temperaturas. Palavras-chave: Degradação, poliuretanos, propriedades mecânicas, variação de propriedades. Study of Ageing of Polyurethanes Applied to the Offshore IndustryAbstract: Brazil is worldwide renowned as a leader in oil and gas extraction in deep and ultra deep water. In the production chain, a great part of the oil and gas produced is conveyed through flexible pipelines that connect the production wells to the platforms. When the pipes are laid on the seabed in a static service condition, the flexible pipes are called flowlines and when raised from the seabed to the platform in a dynamic service condition, they are called risers. The pipes designed for dynamic applications are equipped with bend stiffeners, components with conical form and in general based on polyurethanes, which have the function of providing a transition between the structure of the pipes, of smooth stiffness, and the platform, extremely rigid. This work discussed the changes on the mechanical properties of polyurethanes due to hydrolysis under accelerated ageing. The specimens were exposed at 50, 60 and 70 °C. The mass variation was also evaluated considering that these materials are designed for a service life exceeding twenty years. The polyurethanes presented significant degradation at 70 °C, which can reduce its application time in the field owing to mechanical failures when subjected to high temperatures.

Fasteners manufactured with Inconel 718 alloy are being widely used in offshore and subsea applications due to the material’s high strength, when compared to other nickel alloys, and its inherent corrosion resistance. However, concerns have been raised over its utilization in applications where cathodic protection or impressed current systems are in place. These concerns relate to the susceptibility to hydrogen embrittlement that Inconel 718 alloy may present depending on its processing, microstructure, hardness and actuating stresses. Over the last few years, much has been discussed on the suitability of the alloy for subsea applications. The development of special thermal cycles for the ageing of the alloy has been necessary to provide a consistent material with a maximum hardness of 35 HRc, and a microstructure free of detrimental phases without jeopardizing the overall mechanical properties of the alloy. Wellstream has developed a test programme focused on the assessment of Inconel 718 behavior when subjected to cathodic protection systems. Through this programme, it was possible to demonstrate the suitability of Inconel 718 alloy in subsea applications when the resulting microstructure and hardness are properly controlled, and bolt loading is within normal working limits.

Unbonded flexible pipes are being considered as an actual solution for the following developments for the Brazilian Pre-Salt area. This technology is already being successfully used in the first EWT installed in the Brazilian Pre-salt and being qualified for the first Pre-salt Pilot Project development. However, unlikely the current project developments in water depths around 1500m, the free catenary configuration is not always an applicable option not only due to the 2500m water depth but also to the presence of contaminants such as CO2 and H2S in the conveyed fluids which in certain applications make the use of conventional high strength steels unfeasible, making the use of sour service armour wires mandatory. This paper presents the result of the global and local analysis performed for different applications such as 4″ gas lift, 6″ water injection, 6″ production and 9.13″ Gas export structures designed specifically for the ultra deep water in Brazilian Pre-Salt area. The aim of this study was to verify the feasibility of the free hanging catenary configuration and determine the most suitable flexible pipe system configuration for different applications, confirming that the flexible pipes are an adequate solution for the Pre-Salt even when the service life requirements exceeds 20 years and associated safety factors.

The new offshore areas being explored in Brazil presents higher concentration of CO2 compared with most existing offshore fields. The presence of these more aggressive environments has led to the development of new technologies. Due to the construction characteristics of flexible pipes, any increase in CO2 concentration in the conveyed fluid will, in turn, increase the CO2 concentration in the pipe annulus, subjecting the metallic armor layers to a more aggressive environment. Evaluation of the CO2 effects of corrosion fatigue behavior in tensile armor wires is therefore of vital importance. A comprehensive corrosion fatigue experiment for tensile armor wires in environments up to 10 bar of CO2, has been established and the experimental results have shown a fatigue life reduction in the tensile amour wires due to higher levels of CO2.