Abstract This paper proposes a methodology for the fatigue assessment of concrete coated pipelines during installation using S-lay method. Concrete coating is typically used as a weight coating on larger diameter pipelines for on-bottom stability purposes. Typical offshore concrete coated pipeline consists of 12m pipe joints welded together. Each joint is covered with concrete weight coating (CWC) except at each end where approximately 0.35m length is kept uncovered for welding purposes. The uncovered section of the pipe is called field joint (FJ). The stiffness of the concrete coated section is much higher than the stiffness of field joint. This difference in the stiffness introduces strain concentration at the field joint. Traditionally, fatigue assessment practice does not consider the effect of strain concentration at the field joint. Ignoring strain concentration at the field joint may result in lower fatigue damage estimation which can impact the fatigue life of offshore pipelines. The main objective of this paper is to quantify the strain concentration at the field joint using a simplified method and to study its effect on the fatigue damage during the installation phase. A case study is presented for the installation fatigue of concrete coated pipelines. An FEA based analysis software, Orcaflex is used to conduct static and dynamic installation analysis for the pipelay operation. A simplified method is proposed to estimate the strain concentration at the field joint. Finally, the fatigue assessment is conducted employing the fatigue module in Orcaflex. Fatigue damage results are summarized comparing the concrete coated pipeline with and without the effect of the strain concentration. The results of sensitivity analysis are also given to show the effect of various parameters such as concrete thickness, pipe diameter and water depths on the fatigue damage estimation. The results show that the strain concentration at the field joint has a significant effect on the fatigue estimation for pipelay operation.
Abstract This article highlights the main challenges of subsea processing in the Brazilian pre-salt, focusing on increasing the technological readiness level of critical components that will enable the future deployment of subsea high-pressure CO2 separation and reinjection technology (HISEP) at the FPSO Marechal Duque de Caxias in the Mero field. It also outlines the strategy behind the construction of the Brazilian Pre-salt Technology Center (CTPB) and explains how this facility will help address these challenges. Some pre-salt fields present unique complexities due to their high CO2 content (≥40%) and high gas-to-oil ratio (≥400 Sm3/Sm3), which make gas processing on surface facilities particularly challenging in terms of plant size and weight. Furthermore, the expected increase in GOR over the field's lifetime will place additional constraints on the gas processing plant, ultimately reducing oil production. Another critical factor is the substantial energy demand required to reinject the CO2-rich dense gas stream into the producing reservoirs. In this context, the development of a new technology designed for subsea CO2 separation and reinjection plays a crucial role in enabling efficient debottlenecking of the natural gas processing plant. To complete the final phases of this technology development, the Libra Consortium has contracted a technology supplier to design, construct, and qualify the new subsea high-pressure CO2 separation system. A pilot unit is scheduled for installation at the FPSO Marechal Duque de Caxias in the Mero field in 2028. Mero is the third-largest pre-salt field and the first to be developed under a Production Sharing Contract awarded to the Libra Consortium in 2013. This technology has the potential to debottleneck existing gas processing plants on FPSOs already in production, enabling accelerated production, increased reservoir recovery factor, and reduced greenhouse gas emissions. Once qualified, the new system offers an opportunity to reduce the weight and footprint of topside facilities in the next generation of FPSOs, leading to lower capital expenditure (CAPEX), operating expenditure (OPEX), as well as shorter construction schedules. The Pre-salt Technology Center (CTPB) is a unique experimental facility capable of testing real fluids under conditions that closely replicate those found in the Brazilian pre-salt, including high pressure, high flow rates, elevated salinity, and high CO2 concentrations. While it was initially created to meet the qualification requirements for components of the new subsea high-pressure CO2 separation technology, its distinctive capabilities now also support the testing of new processing and fluid-measurement technologies for both subsea and topside applications, including Carbon Capture, Utilization, and Storage (CCUS). This article highlights the key challenges associated with production in ultra-deepwater scenarios in the Brazilian pre-salt region, as well as the contribution of the CTPB to the development of this new subsea high-pressure CO2 separation technology. It also showcases the CTPB's experimental infrastructure and its role in qualifying critical components and pioneering new fluid separation and treatment processes for offshore applications.
The hybrid subsea foundation (HSF), which combines shallow-skirted mudmats with tubular pin piles, is widely used in deepwater subsea developments because it can accommodate substantial vertical and lateral forces and overturning moments from in-line structures (ILS) such as pipeline end transmission (PLET), pipeline end manifold (PLEM), and in-line tee (ILT). Recent field and numerical studies (Gaudin et al. 2012; Dimmock et al. 2013; Hossain et al. 2015; Won et al. 2015, 2018; Demel et al. 2016; Jang and Suroor 2017) indicate that the HSF substantially improves system capacity, with reported increases in overall load capacity of three times (Demel et al. 2016). However, a formal design guideline for HSFs has not yet been established. Early HSF concepts developed by Gaudin et al. (2012) and Dimmock et al. (2013) followed a design philosophy in which pin piles were intended to resist lateral loads and overturning moments while the mudmat carried the vertical loads. Those studies generally did not include the vertical bearing contribution of the pin piles, even though the foundation's moment capacity is affected by pile axial resistance. Treating the mudmat and pin piles as interacting elements rather than as independently acting components can therefore unlock additional efficiency and performance gains. To realize such combined behavior, reliable mechanical integration between pile heads and the mudmat is required; Won et al. (2015) proposed a pile-head locking system to transfer both the vertical and lateral loads into the piles, thereby reducing the required mudmat footprint by mobilizing the axial and lateral capacities of the pin piles. Subsequent investigations have explored these ideas further. Hossain et al. (2015) presented a case study where pin piles were designed to resist the vertical loads in addition to lateral loads and overturning moments and highlighted that the performance of the system depends on both combined load interactions and the sequence of loading. Jang and Suroor (2017) used numerical modeling to quantify the effects of multidirectional loading on the capacity of the HSF through failure envelopes. Won et al. (2018) reported a project case where a customized pile-head locking system was used to account explicitly for pin-pile vertical resistance alongside lateral capacity. Most prior studies, however, have evaluated HSF performance under the most onerous operational loading without accounting for time-dependent soil processes beneath the mudmat.
Introduction:The 1987 UHMS Workshop on the Validation of Decompression Tables provided standards for the design, testing, and acceptance of decompression tables. Forty years later, research funding has become scarce, and diving companies no longer receive support from universities and Navy research centers. Companies build on their experience and safety culture to improve existing decompression procedures. We list principles and propose guidelines for these internal developments. Principles:Editing decompression tables is a technical activity that aims to provide a practical solution to an immediate operational problem. It relies heavily on current scientific knowledge and experience and on recognized design principles, validation protocols, and acceptance criteria. Validation:Validating decompression procedures fits into the company's Health and Safety management system. Today, decompression tables result from a risk assessment and are presented as a mitigation measure against decompression risks. Management of Change offers a step-by-step approach compatible with the UHMS recommendation for improving existing procedures. Acceptance:Accepting decompression procedures is based on the definition and measurements of relevant endpoints used as acceptance criteria. Endpoints have evolved from DCS incidence to the larger concept of decompression stress. We highlight the importance of dive monitoring in documenting procedure performances and supporting the acceptance decision. Discussion:We conclude that Management of Change can be used by diving companies to develop new or revised decompression procedures, as a complement to the 1987 UHMS recommendations. We recommend that the process be detailed in the company documentation to keep the lessons learned and inform operational personnel.
This article presents a probabilistic approach for lateral buckling analysis based on a global finite element (FE) model via a case study of a 5 km long subsea flowline with sleeper mitigators on an undulating seabed. In the case study, axial/lateral pipe-soil interaction, pipe/sleeper friction factors (FF), and horizontal out-of-straightness (OOS) of flowline at seabed and sleepers are defined as stochastic parameters, while other parameters, including flowline as-laid vertical OOS, pipe section, and operating parameters, are defined as deterministic variables. First, the response surfaces for lateral buckling of the full-length flowline due to the stochastic parameters are created through FE analyses based on a load case matrix selected by the design of experiment approach. Then, Monte Carlo simulations based on the response surfaces are performed to obtain the distributions of lateral buckling responses, including parameters such as the limit states for postbuckle, buckle amplitudes, walking speed or end pile loads, rogue, and engineered buckle locations. Finally, the probability distributions of the limit-state unity checks are compared with the target failure probabilities. This probabilistic approach will require more simulation time compared to the deterministic approach but can provide more detailed probability ranges for the lateral buckling responses and save the project on total cost. This approach can be used to assess the reliability of lateral buckling responses during the detailed design phase of subsea pipelines susceptible to lateral buckling.
