Design life of offshore structures is in general in the 20- to 30-year range, with some cases going up to 50 years. Fatigue is one of the major design criteria for such structures. Climate change may affect the fatigue life of offshore structures, it would be necessary to update the design procedures to take into account climate change effects on structural performance. This paper aims to investigate the impact of climate change in the long-term fatigue life of offshore structures due to wave loading. For this purpose, available environmental conditions for two locations (South East Brazilian Coast and North Atlantic Ocean) generated by the HadGEM-2S global climate model, considering representative concentration pathway (RCP) 4.5 and RCP 8.5 future scenarios and the historical (past) scenarios are considered. The assessment in both locations is performed for two structural models: an idealized stress spectrum for a generic fatigue hot-spot and a steel lazy wave riser (SLWR) connected to a floating production storage and offloading (FPSO). Fatigue life is estimated using the S–N curve approach. Results show that the impact on the fatigue life depends on the structure dynamic characteristics, on the geographic location and mainly on the greenhouse emission scenario. In general, for the Brazilian location, when compared to the historical scenario, most of the future scenarios lead to slightly higher fatigue damages (lower fatigue lives). On the other hand, for the North Atlantic location, there is not a clear trend for future climate change scenarios.

Short-term extreme response estimates are required in many areas of ocean and offshore engineering, such as steel risers design. As in many cases, the response in non-Gaussian, a theoretical solution, is usually not readily available for this purpose. Hermite transformation and Weibull-based models, among others, are some alternatives that have been used in connection with sampled response time series. In this work, a new approach is investigated. Recently, a four-parameter distribution known as the shifted generalized lognormal distribution (SGLD) has been presented in the literature. One of its main advantages is that it covers regions of skewness–kurtosis not covered by other distributions of common use in engineering. In this paper, the performance of this distribution is evaluated in the extreme values' estimation of the utilization ratios of steel riser sections. Three alternatives for using SGLD are investigated in two case studies of different dynamic behavior. The first one is a steel-lazy wave riser (SLWR) connected to a turret-moored FPSO (floating, production, storage and offloading unit) in 914 m water depth, and the second is a SLWR connected to a spread-mooring FPSO in a water depth of 1400 m. The results obtained by the SGLD-based analysis, which considered several simulation lengths, are compared to those obtained by means of an extreme value distribution fitted to episodical extremes obtained from many distinct realizations. The results of a traditional Weibull-fitting approach to the response peaks and those obtained with a Hermite transformation-based model are also presented for comparison.

Traditionally, fatigue life calculations are very expensive in terms of time and computer resources. They are usually performed during riser design phases, when several lines with similar characteristics need to be analyzed. While operating, when problems are detected, fatigue analyses are also necessary to help to decide if any action is needed. In both situations, end fittings and bendstiffeners are usually the critical regions. Considering the high number of flexible risers installed in Brazil and the structural complexity of this kind of structure, a robust and fast methodology to evaluate the fatigue life of flexible risers becomes attractive. In this way, this paper proposes a analytical/numerical methodology to evaluate the fatigue life at the top region of flexible pipes. Using the top imposed motions and taking into account the properties of all structures in the riser, it is possible to evaluate tension analytically. Combining tension and the rotations imposed at the top of the riser, curvatures are determined, and stresses can be calculated. Finally, SN curves and the Miner’s rule for damage accumulation allow the estimation of fatigue life. The obtained results indicate that the proposed methodology is conservative when compared to traditional ones. Also, it is very fast, allowing the fatigue life estimation in minutes.

Until recently, risers were designed considering only few regular sea analyses and high safety factors. The increase of the computers processing capability and the simultaneous reduction of their costs, however, allowed riser designers to change their project procedures. Nowadays, risers can be designed considering not only much more analyses, but also more complex ones. Following this new tendency, methodologies that aim to reduce the computational costs of random analyses represent an important research line. The main purpose of this work is to develop a methodology based on polynomial models to predict time series of a riser response parameter. This methodology considers as inputs the movements of the platform caused by wind, wave and current. The desired response parameter investigated in this paper is the top tension, although the procedure to evaluate stresses is very similar. This methodology can be applied in the initial phases of the riser project, accelerating the selection of a structure that satisfies project criteria, and in the representation of the riser dynamic response in coupled analyses, reducing their computational costs.

During drilling operations, the wellhead system and casings shall be designed to support cyclic loads from the connected riser and the BOP stack. Cyclic loadings can lead to large well head motions and therefore fatigue becomes a major concern for well designers, receiving great attention in recent years. The accumulation of damage is dependent on several aspects, such as the