The response of one-degree-of-freedom systems with frictional devices (Coulomb oscillators) undergoing Gaussian support motion (earthquake) is investigated by adopting a moment equation approach in the context of Itoˆ's calculus. Such equations contain expectations of the signum function of the velocity. In order to evaluate them, the joint probability density function of the variables is expanded in a truncated series of modified Hermite polynomials, which allows the computation of the response moments. The truncation is equivalent to neglecting the Hermite moments of the variables 381 382 FATICA AND FLORIS beyond a given order. Starting from the response moments so calculated, approximate marginal and joint PDF, mean upcrossing rate functions, and the largest value distributions can be constructed. Conversely, the estimates of the response correlations require the evaluation of a first-order differential system, which also is written by using Itoˆ's rule. The results of the applications compare well with the simulation, and show that the assumption of Gaussian response is unacceptable and non-conservative.

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This paper reports the Lessons Learned from an innovative linepipe solution that was successfully implemented on P55 Deepwater Project. The P55 field is located offshore Brazil, in the northern area of Campos Basin, in a water depth ranging from 1500m to 1900m. The scope of work consisted in engineering, procuring, fabricating and installing 16 rigid Steel Catenary Risers (SCRs), which are the first of their kind in this area. The corresponding 12-inch SCR qualification results are presented in the perspective to show the significant benefits of the technology used and its potential developments to High Pressure & High Temperature applications.In order to meet tight Hi-Lo requirements together with high fatigue performances, innovative Pipe End Design and associated automatic welding procedures were developed and qualified. The paper describes the complete sequence of pipe manufacturing process, from hot-rolling to final machining, which resulted in a concentric and reproducible pipe end geometry, ideal for limiting Stress Concentration Factors.An extensive qualification program of Full Scale Fatigue test was conducted on girth-welded strings and the associated results showed performance levels at least four times above the target curve. Moreover, Lessons Learned from the offshore campaign established that developed Pipe End Design led to significant improvements in welding times and subsequent J-laying rates. Details on how the technology effectively reduces critical times and lowers rejection rates are provided on the basis of the actual P55 offshore campaign.In addition to the advantages detailed in the paper, the presented linepipe solution proves to be also applicable to High Temperature fields, since the enhanced fatigue behavior was found to compensate a temperature derating up to 270°C. In fact, the presented manufacturing and welding technologies have opened the perspective of ongoing Developments, which are believed to bring a reliable solution for combined High Pressure and High Temperature applications.

The exploitation of subsea hydrocarbons fields as well as large subsea gas to market infrastructures often requires pipelines to route across sharp slope transitions. Site conditions are sometime so critical to represent a severe design concern and to require costly seabed preparation works, extremely challenging and environmentally impacting. This paper presents an innovative solution that allows avoiding any preparation work as well as a novel installation method for its effective and safe implementation. Specifically, the paper presents a design case study for a gas export pipeline crossing a severe escarpment at the intersection between the Continental Shelf and the Continental Slope (Shelf Break). The rigid pipeline installed by normal continuous pipelay across such sharp slope transition would be subject to excessive bending due to localized imposed curvature that requires mitigation. Two alternative design solutions have been developed and compared: one based on excavation (trenching) to shape the escarpment edge and one introducing vertical bends on the pipeline string. The design solution based on trenching results in large excavation volume with associated environmental impact in term seawater turbidity and damaged seabed surface (biocenosis). The analysis results also show that the solution is very sensitive to trenching profile accuracy and profile long term stability. Constructability is discussed in terms of availability of technology vs water depth, soil uncertainties, excavation volume, excavation tolerances. The alternative design based on bends allows avoiding any seabed preparation works and all the associated issues. The analysis results demonstrate much higher performances in terms of pipeline integrity and safety throughout the pipeline life. However, its implementation requires special installation solutions as bends are not installable with the normal continuous pipelay method. The paper presents a new installation method (Saipem patented) that allows realizing vertical cold bends safely and effectively on the pipeline profile with no interruption of the continuous pipelay process. The novel idea is to realize the bends underwater, when the pipe is landing or close to landing on the seabed, by means of a remotely operated Underwater Bending Machine purposedly designed. The paper describes the new Underwater Cold Bending technology, presenting the engineering work done to support the demonstration of its robustness and reliability. The paper also presents a case study for escarpment crossing design developed according to two alternative design concepts, the standard and the novel one. The two solutions are compared, listing pros and cons of each one, highlighting relevant design issues as well as construction criticalities and risks.