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A comprehensive overview of managing and assessing safety and functionality of ageing offshore structures and pipelines A significant proportion, estimated at over 50%, of the worldwide infrastructure of offshore structures and pipelines is in a life extension phase and is vulnerable to ageing processes. This book captures the central elements of the management of ageing offshore structures and pipelines in the life extension phase. The book gives an overview of: the relevant ageing processes and hazards; how ageing processes are managed through the life cycle, including an overview of structural integrity management; how an engineer should go about assessing a structure that is to be operated beyond its original design life, and how ageing can be mitigated for safe and effective continued operation. Key Features: * Provides an understanding of ageing processes and how these can be mitigated. * Applies engineering methods to ensure that existing structures can be operated longer rather than decommissioned unduly prematurely. * Helps engineers performing these tasks in both evaluating the existing structures and maintaining ageing structures in a safe manner. The book gives an updated summary of current practice and research on the topic of the management of ageing structures and pipelines in the life extension phase but also meets the needs of structural engineering students and practicing offshore and structural engineers in oil & gas and engineering companies. In addition, it should be of value to regulators of the offshore industry.

Sulfate induced degradation of concrete brings great damage to concrete structures in saline or offshore areas. The degradation mechanism of cast-in-situ concrete still remains unclear. This paper investigates the degradation process and corresponding mechanism of cast-in-situ concrete when immersed in sulfate-rich corrosive environments. Concrete samples with different curing conditions were prepared and immersed in sulfate solutions for 12 months to simulate the corrosion of precast and cast-in-situ concrete structures, respectively. Tests regarding the changes of physical, chemical, and mechanical properties of concrete samples were conducted and recorded continuously during the immersion. Micro-structural and mineral methods were performed to analyze the changes of concrete samples after immersion. Results indicate that the corrosion process of cast-in-situ concrete is much faster than the degradation of precast concrete. Chemical attack is the main cause of degradation for both precast and cast-in-situ concrete. Concrete in the environment with higher sulfate concentration suffers more severe degradation. The water/cement ratio has a significant influence on the durability of concrete. A lower water/cement ratio results in obviously better resistance against sulfate attack for both precast and cast-in-situ concrete.

Corrosion-induced deterioration of the in-service marine reinforced concrete (RC) structures may result in unsatisfactory serviceability or insufficient safety. Surface deterioration analysis based on random fields can provide information regarding the future development of the surface damage of the in-service RC members, but its accuracy needs to be verified in order to broaden its applications in durability assessment. This paper performs an empirical study to verify the accuracy of the surface deterioration analysis based on random fields. The batch-casting effect is considered to establish the “step-shaped” random fields for stochastic parameters in order to better coordinate their actual spatial distributions. Inspection data from a 23-year-old high-pile wharf is obtained and analyzed in this study. The simulation results of the RC panel members’ surface deterioration are compared with the in-situ inspection results with respect to the steel cross-section loss, cracking proportion, maximum crack width, and surface damage grades. It shows that the simulation results coordinate well with the inspection results. On this basis, four maintenance options are established and compared in terms of the total amounts of RC panel members needing restoration and the total economic costs. It provides a comparative tool to aid the owners in selecting the optimal maintenance action given the inspection results, to minimize the lifecycle cost and guarantee the sufficient serviceability and safety of the structures.

River silt deposited by water in coastal areas is unsuitable for engineering construction. Thus, the in situ stabilization treatment of river silt as the bearing layer has been an important research area in geotechnical engineering. The strength degradation behavior and mechanism of stabilized river silt reinforced with cement and alginate fibers (AFCS) in different engineering environments are crucial for engineering applications. Therefore, freeze–thaw (F–T) cycle tests, wetting-drying (W–D) cycle tests, water immersion tests and seawater erosion tests were conducted to explore the strength attenuation of stabilized river silt reinforced with the same cement content (9% by wet weight) and different fiber contents (0%, 0.3%, 0.6% and 0.9% by weight of wet soil) and fiber lengths (3 mm, 6 mm and 9 mm). The reinforcement and damage mechanism of AFCS was analyzed by scanning electron microscopy (SEM) imaging. The results indicate that the strength of AFCS was improved from 84% to 180% at 15 F–T cycle tests, and the strength of AFCS was improved by 26% and 40% at 30 W–D cycles, which showed better stability and excellent characteristics owing to the hygroscopic characteristics of alginate fiber arousing the release of calcium and magnesium ions within the alginate. Also, the strength attenuation of AFCS was reduced with the increase in the length and content of alginate fibers. Further, the strength of specimens in the freshwater environment was higher than that in the seawater environment at the same fiber content, and the softening coefficient of AFCS in the freshwater environment was above 0.85, indicating that the AFCS had good water stability. The optimal fiber content was found to be 0.6% based on the unconfined compressive strength (UCS) reduction in specimens cured in seawater and a freshwater environment. And the strength of AFCS was improved by about 10% compared with that of cement-stabilized soil (CS) in a seawater environment. A stable spatial network structure inside the soil was formed, in which the reinforcing effect of fibers was affected by mechanical connection, friction and interfacial bonding. However, noticeable cracks developed in the immersed and F–T specimens. These microscopic characteristics contributed to decreased mechanical properties for AFCS. The results of this research provide a reference for the engineering application of AFCS.

Long-term creep properties and the effect of water are important for fiber reinforced polymer (FRP) composite materials used in offshore applications. Epoxies are often used as a matrix material in such composites. A typical design lifetime of offshore FRP structures is 25 or more years in direct contact with water leading to some deterioration of the material properties. Knowing and predicting the extent of the material property deterioration in water is of great interest for designers and users of the offshore FRP structures. It has been established that the time–temperature superposition principle (TTSP) is a useful tool for estimating changes in properties of polymer materials at long times or extreme temperatures. In this work, a time–temperature–plasticization superposition principle (TTPSP) is described and used for predicting the long-term creep behavior of an epoxy compound. The studied epoxy does not degrade chemically via hydrolysis or chain scission but is negatively affected by plasticization with water. The methodology enables prediction of the long-term viscoelastic behavior of amorphous polymers at temperatures below the glass transition (Tg) using short-term creep experimental data. The results also indicate that it is possible to estimate the creep behavior of the plasticized polymer based on the short-term creep data of the respective dry material and the difference between Tg values of dry polymer and plasticized polymer. The methodology is useful for accelerated testing and for predicting the time-dependent mechanical properties of a plasticized polymer below the glass transition temperature.

Concrete, a versatile construction material, faces pervasive deterioration due to microbiologically influenced corrosion (MIC) in various applications, including sewer systems, marine engineering, and buildings. MIC is initiated by microbial activities such as involving sulfate-reducing bacteria (SRB), sulfur-oxidizing bacteria (SOB), etc., producing corrosive substances like sulfuric acid. This process significantly impacts structures, causing economic losses and environmental concerns. Despite over a century of research, MIC remains a debated issue, lacking standardized assessment methods. Microorganisms contribute to concrete degradation through physical and chemical means. In the oil and gas industry, SRB and SOB activities may adversely affect concrete in offshore platforms. MIC challenges also arise in cooling water systems and civil infrastructures, impacting concrete surfaces. Sewer systems experience biogenic corrosion, primarily driven by SRB activities, leading to concrete deterioration. Mitigation traditionally involves the use of biocides and surface coatings, but their long-term effectiveness and environmental impact are questionable. Nowadays, it is important to design more eco-friendly mitigation products. The microbial-influenced carbonate precipitation is one of the green techniques and involves incorporating beneficial bacteria with antibacterial activity into cementitious materials to prevent the growth and the formation of a community that contains species that are pathogenic or may be responsible for MIC. These innovative strategies present promising avenues for addressing MIC challenges and preserving the integrity of concrete structures. This review provides a snapshot of the MIC in various areas and mitigation measures, excluding underlying mechanisms and broader influencing factors.

The service life prediction of reinforced concrete (RC) structures in marine environment is essential in structural repair and health monitoring. In this paper, a numerical model for predicting the service life of reinforced concrete is first developed which considering the time-varying boundary of chloride concentration, critical chloride concentration and density of corrosion current. Based on the model, the effects of water–cement ratio, reinforcement diameter, concrete cover thickness and critical chloride ion concentration on the service life and deterioration duration of RC structures are investigated. The key factors affecting the service life of reinforced concrete structures are determined. More importantly, based on regression analysis, a new simplified empirical model for predicting the service life of RC structures is also developed. It provides a fast assessment tool for practical engineers. Both the numerical model and empirical model validated are suitable for practical engineering applications. The results show that with the increase of water–cement ratio, the service life of reinforced concrete structure decreases exponentially. And with the increase of the thickness of the concrete cover, the service life, deterioration duration, and safety reserve increase linearly. However, the influence of the diameter of the reinforcing bar on the service life can be ignored.

Wang, Z.-S.; Li, Y.-K.; Lu, J.-L.; Tian, J.-B., and Zhao, K., 2020. Research on corrosion characteristics and performance degradation of basalt fiber concrete under sodium magnesium sulfate corrosion environment. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 56–62. Coconut Creek (Florida), ISSN 0749-0208. As the most commonly used building material for marine structures, concrete is seriously corroded by marine environment. As a green, high-performance material, basalt fiber can improve the mechanical and corrosion resistance of concrete materials. The research conducted experimental research and analysis on the durability and mechanical properties of basalt fiber concrete under the erosion of magnesium sulfate and sodium sulfate. The test block is 100 mm × 100 mm × 100 mm, and the fiber content is 0%, 0.05%, 0.1%, 0.2%, 0.3%, respectively, soaked in the magnesium sulfate and sodium sulfate solution with a concentration of 5.0%. The apparent cracks and water absorption were observed every 30 days. The mechanical properties and the ion concentration were measured every 90 days. The main conclusions are as follows: basalt fiber has a certain increase in the bearing capacity and deformability of concrete. Compared with ordinary concrete in a sulfate environment, basalt fiber concrete has a slower increase in porosity; however, excessive fiber will adversely affect durability. When the basalt parameter is about 0.1%, it is the most economical and reasonable, this study will provide a certain research basis for the application of basalt fiber concrete in marine structures.

Lead rubber isolation bearings are well-recognized as a common and effective means to mitigate the seismic responses of bridges. However, rubber isolation bearings used in offshore bridges are extremely vulnerable to the action of the alternation of aging and seawater erosion caused by weather conditions, wind, waves, and other factors. Meanwhile, the deterioration law and application of lead rubber bearings subject to the effect of aging and seawater erosion cycles are not clear. Thus, aging and seawater erosion cycles testing on both lead rubber isolation bearings (LRB) and rubber materials were carried out. The parameters for the Mooney–Rivlin model of the rubber material used in LRBs were determined and the time-varying law of basic performance of LRBs was obtained based on test results of LRBs and their rubber material. Then, the determined rubber material parameters were applied into the finite-element model of LRBs to verify the basic performance degradation law of the LRBs. Finally, the obtained basic performance degradation law of LRBs was substituted into the finite model of offshore bridges to investigate the impact of the property degradation of LRBs on their seismic performance. The time-varying law of seismic performance of offshore bridge structures was also studied based on finite element analysis. The results show that both the horizontal and vertical stiffness of LRBs increase with the alternating of aging and seawater erosion time, and the horizontal and vertical stiffness increase by 16.1% and 24.3%, respectively, during the 120-year service period. Additionally, the Mooney–Rivlin model parameters of the LRB rubber material are also significantly affected by the alternating of aging and seawater erosion. Additionally, the results also indicate the deterioration of LRBs has a great influence on the anti-seismic performance of offshore bridge structures. After 120 years of service of offshore bridge isolation bearings under the alternating of aging and seawater erosion, the maximum displacement of the pier top of the offshore bridges, the maximum bending moment at the pier bottom, and the maximum displacement of the rubber bearing increased by 14.2%, 6.6%, and 9.1%, respectively. The findings of this paper play an important role in the seismic behavior study and the life-cycle performance analysis of offshore traffic projects such as sea-crossing bridges in marine environments. At the same time, they also lay a theoretical foundation for the performance analysis of rubber isolation bearings and offshore bridge structures under the alternation of aging and seawater erosion cycles.