Wei-Liang Jin

Risk Assessment Methodology

This chapter discusses risk assessment methodology. From the viewpoint of the environmental protection, the leakage of hydrocarbon from pipelines and risers, tankers, and facilities shall meet the required standard. Risk assessment is a tool for the management of safety, health, and environmental protection. The purpose of this chapter is to discuss the basic procedures for the risk assessment. Furthermore, this chapter explains risk concepts and risk acceptance criteria. LR published guidelines for classification using risk assessment techniques to determine performance criteria. This chapter discusses an overview of risk assessment. The main steps of a risk assessment are planning of risk analysis, system description, hazard identification, analysis of causes and frequency of initiating events, consequence and escalation analysis, and identification of possible risk reducing measures. To quantify accident frequency or causes, it is particularly important to establish a reliable data basis. The data basis should be consistent with relevant phases and operations. Risk estimation and risk reducing measures are explained in this chapter. Risk acceptance criteria define the overall risk level that is considered as acceptable, with respect to a defined period of the activity. They are a reference for the evaluation of the need for risk reducing measures, and therefore should be defined prior to initiating the risk analysis. This chapter also discusses the use of risk assessment to determine performance standard.

Risk-Based Decision-Making

Most participants in maritime and other industries are continually faced with difficult decisions. It is a simple fact that the major hazards of today are more difficult to observe and evaluate than were the major hazards of the past. There are five known factors discussed in this chapter that contribute to the growing difficulty in making “good” decisions. Uncertainties and variability cover every aspect of the maritime industry from design, through construction and operation, until the final scrapping of a ship, platform, or facility. Variabilities in material properties, construction techniques, and operations are an everyday fact of life in any technical field. The field of risk-based decision-making (RBDM) was developed in order to deal with these uncertainties. RBDM allows uncertainties to be characterized and integrated into activities such as planning, crisis prevention, and management. RBDM methods form a process by which decisions can be made regarding safety, durability, serviceability, and compatibility. To use RBDM methods, the fundamentals of probability and statistics are reviewed first. The basic principles of RBDM will then be discussed. These precepts will be expanded upon in the following chapter.

Basics of Structural Reliability

This chapter discusses structural reliability methods for the design of marine structures with emphasis on their practical application—for example, in ship structures. Focus is given to basic concepts, methodologies, and applications. Examples are given to demonstrate the application of the methodology. This chapter discusses simple analytical equations that are based on lognormal assumptions. The papers on numerical approaches are also mentioned briefly. This chapter explains the following subjects in detail: reliability of marine structures, reliability-based design and code calibration, fatigue reliability, probability, and risk-based inspection planning, etc. In general, a marine structural analysis deals with the load effects and the structural strength. Uncertainty analysis is the key in any reliability evaluation, such as reliability-based design and requalification for marine structures, which is explained in this chapter. Certain concepts are introduced in this chapter for the reliability evaluation at a component level, which means that the concern is on the failure probability of problems modeled by a single limit-state function. The system reliability analysis section deals with the formulation and evaluation of failure probability in problems where more than one limit-state function must be considered (i.e., system reliability analysis). Reliability methodology can be used as a tool to reassess structural integrity. Target probabilities are chosen to minimize total expected costs over the service life of the structure. A cost–benefit analysis approach may be used effectively to define target probability for design in which failures result in only economic losses and consequences.

Risk Assessment Applied to Offshore Structures

This chapter discusses the issue of risk assessment applied to offshore structures. There are several types of offshore risks, like structural and marine events, collisions, fires, dropped, objects, blowouts, risers/pipelines leaks, process leaks, and transport accidents. The most frequent occurring collisions are the impacts of offshore supply vessels and platforms. Collision risks are detailed with subsections such colliding vessel categories, collision frequency, collision consequence, and collision risk reduction. Explosion risks are also explained in this chapter, from explosion frequency to risk reduction. Fire risk description includes fire frequency, fire load and consequence assessment, and fire risk reduction. It also covers guidance on fire and explosion design. Dropped objects are another item discussed in this chapter. This chapter deals with case study risk assessment of floating production systems. The process systems include a process plant with three-stage separation, gas compression for export and gas turbine-driven power generation on deck, piping, pressure vessels in production and storage facilities and cargo tanks, and crude pumping systems, offloading systems, and operations. Marine systems comprise cargo tanks, crude pump rooms, boilers and engine rooms, power generation/supply systems, ballast systems, wing tanks, etc. Hazard identification is another area covered in this chapter.

Risk Centered Maintenance

This chapter discusses risk-centered maintenance. It describes the application of risk analysis to maintenance of facilities on offshore installations. It mainly consists of preliminary risk analysis (PRA) and reliability-centered maintenance (RCM). This chapter is conceived to be a guide for the development and optimization of maintenance strategies. The roles of PRA and RCM in the maintenance process are illustrated in this chapter. The maintenance of offshore facilities presents many unique difficulties, which are not usually encountered in inland applications, and are mentioned here. The RCM history is also explained in this chapter. Screen operating units within a plant are used to identify areas of higher risk, and assign a risk level to each equipment item based on a consistent methodology task. The RCM is defined as a process for determining what must be done to ensure that any equipment/facility continues to do whatever its users expect it to do. The main focus of RCM is hence on the system functions, and not on the system hardware. It is very important that the RCM team decides on which level the analysis shall be carried out in the initial phase of the RCM process. Failure propagation may be categorized as gradual failure, aging failure, and sudden failure. The optimization of maintenance task intervals usually requires a quantitative analysis. The detailed description of the optimization process is not within the scope of this book.

Offshore Structures Under Earthquake Loads

This chapter discusses offshore structures under earthquake loads. A procedure based on the finite element and plastic node methods is proposed for the earthquake response analysis of three-dimensional frames with geometric and material nonlinearities. Using the proposed procedure, the earthquake response of a jacket platform is investigated. Bottom-supported offshore structures in seismic areas may be subjected to intensive ground shaking that causes structures to undergo large deformations well into the plastic range. The present chapter is devoted to time–domain solutions that allow the development of plastic deformations to be examined in detail. There is the need for a procedure to predict the earthquake response of offshore structures that includes both geometric and material nonlinearities, and such a procedure for the earthquake response analysis of three-dimensional frames is presented. In conjunction with the plastic node method, the proposed approach enables the accurate modeling of frames using only one element per physical member. Element stiffness matrices are evaluated without the numerical integration usually required by traditional finite element methods. This approach can also be applied to the nonlinear dynamic response analysis of offshore structures under collision loads. In the analysis of a structure subjected to strong earthquake loading, it is important to take both geometric and material nonlinearities into account.

Green Ship Concepts

Green ship means the ship with advanced environmental friendly technologies that reduce greenhouse gases or air pollutants generated during the voyage. The technologies are divided into large three parts: reducing emissions, improving the efficiency of energy, and developing propulsion power. Currently, environmental regulation systems make shipping industries more competitive. Shipping industries are now making an effort to develop fuel-efficient ships to compete with other global companies. The EEDI (Energy Efficiency Design Index), indicated by the quantity of CO 2 allowed during transportation in units of freight per distance, was enforced in 2013. The purpose of this chapter is to provide a few green technologies to meet the newly enforced rules, specifically emission technology, because it plays a large role in the greenhouse effect.

Ultimate Strength of Cylindrical Shells

This chapter discusses the ultimate strength of cylindrical shells. The effects of residual stresses and geometric imperfections are implicitly accounted for in the criteria discussed in this chapter. However, if the fabrication tolerance is violated, or dents and significant corrosion defects are found in in-service structures, repair and additional strength analysis are necessary. Cylindrical shells are important structural elements in offshore structures, submarines, and airspace crafts. They are very often subjected to combined compressive stress and external pressure, and must be designed to meet strength requirements. In the elastic region, studies carried out in this field indicate that the buckling stress in bending is close to that for buckling in axial compression, for all practical purposes. The effect of boundary conditions may also play an important role, affecting the buckling strength of unstiffened short shells under bending. The shorter the cylinder, the higher the buckling strength; this is because prebuckling deformation, which is less for shorter cylinders, may reduce shell buckling strength. The section on the buckling of ring-stiffened shells discusses the ultimate strength of cylindrical shells strengthened by ring frames that are subjected to axial compression, external pressure, and their combinations. Potential failure modes include local buckling of the panels between stringer stiffeners, stringer buckling, general instability, local stiffener tripping, and interaction of the above failure modes.

A Theory of Nonlinear Finite Element Analysis

This chapter discusses the theory of nonlinear finite element analysis. A variety of situations exist, in which a structure may be subjected to large dynamic loads, which can cause permanent deformation or damage to the structure. Therefore, structural dynamics and impact mechanics have an important role in the engineering design. This chapter presents a simple and efficient procedure for the large displacement plastic analysis of beam-column elements. The objective of this chapter is to present a theoretical formulation for the modeling of strain-rate hardening effects, and show how these effects can be implemented in three-dimensional finite beam-column elements. The finite beam-column element is ideally suited for the impact analysis of flames with large displacements, strain hardening, and strain-rate hardening. The accuracy and efficiency of the element are examined by comparing the present results with those obtained from experiments by others, from rigid-plastic analyses, and from the existing finite element analysis results. This appendix is written based on a Japanese book authored by Yagawa and Miyazaki. When the formulation presented in this chapter was made, the author had been inspired by this book and that by Yamada. The objective of this appendix is to describe the basics of plasticity that may be useful for understanding the mathematical formulation presented in the main body of this chapter. The isotropic hardening rule and the kinematic hardening rule are also described.

Reliability of Ship Structures

This chapter discusses the reliability of ship structures. The earliest applications of reliability methods to ship structures focused on overall hull girder reliability subjected to wave bending moments. Recent work in applying reliability methods to the ultimate strength of gross panels using second-moment methods has shown considerable promise. Time-variant structural reliability assessment of an FPSO hull girder relative to ultimate strength requires consideration of three aspects: load effects and their combinations; the hull ultimate strength; and methods of reliability analysis. Environmental severity factors are introduced to fit the wave-induced bending moments after accounting for site-specific conditions. A methodology is presented for time-variant reliability assessment relating to the ultimate strength of the midsection for hull girders subjected to the structural degradations of corrosion and fatigue. It includes three aspects of closed-form equations for assessment of the hull girder reliability; load effects; load combination; and time-variant reliability. Also discussed is the procedure for reliability analysis of ship structures. The reliability analysis of existing ships should be covered by the basic steps of the next section. It is concluded that load combination factors obtained from the Ferry–Borges method are dependent on the mean arrival rate of still-water bending moments (SWBMs), the service lifetime, and environmental severity factors.