Gilberto Francisco Martha de Souza

Reliability concepts applied to cutting tool change time

This paper presents a reliability-based analysis for calculating critical tool life in machining processes. It is possible to determine the running time for each tool involved in the process by obtaining the operations sequence for the machining procedure. Usually, the reliability of an operation depends on three independent factors: operator, machine-tool and cutting tool. The reliability of a part manufacturing process is mainly determined by the cutting time for each job and by the sequence of operations, defined by the series configuration. An algorithm is presented to define when the cutting tool must be changed. The proposed algorithm is used to evaluate the reliability of a manufacturing process composed of turning and drilling operations. The reliability of the turning operation is modeled based on data presented in the literature, and from experimental results, a statistical distribution of drilling tool wear was defined, and the reliability of the drilling process was modeled.

Structural Life Expectancy of Marine Vessels: Ultimate Strength, Corrosion, Fatigue, Fracture, and Systems

This paper provides a methodology for the structural reliability analysis of marine vessels based on failure modes of their hull girders, stiffened panels including buckling, fatigue, and fracture ...

Application of Markov Chain to Determine the Electric Energy Supply System Reliability for the Cargo Control System of LNG Carriers

The natural gas industry, as well as other industrial activities, is not free from accidents, which can cause serious consequences to the integrity of people and properties. For this reason, it is necessary to develop studies to determine what are the possible causes of LNG leakage during the loading or unloading operation. This paper aims to determine the reliability of the Cargo control system electric power supply system applying Markov Chain technique. This reliability modeling tool is used because the system consists of several components in passive parallel. Based on the reliability analysis maintenance recommendations are proposed aiming at reducing system failure probability.The method used in this paper is divided in three steps. The first step consists in carrying out a study to identify what are the components that are part of electric power supply system. The second step involves the reliability analysis of the electric energy supply system. Finally some maintenance recommendations are presented aiming at reducing system failure rate. This analysis is used for the analysis of a LNG carrier operating in a Brazilian harbor indicating the most probability failure modes of this system and the most suitable maintenance actions to avoid them.Copyright

Fundamentals of Maintenance

The pieces of equipment installed in a thermal power plant must be subject to very stringent maintenance policies aiming at maintaining their operational availability. Those policies must be centered on controlling the aging degradation that affects mechanical equipment reliability. Furthermore the maintenance policy must account for economical and safety aspects associated with the failure of some critical equipment that constitutes the power plant. The use of Reliability-Centered Maintenance concepts is discussed as a suitable method to define equilibrium between the failure effects associated with the occurrence of critical equipment failure and the costs associated with maintenance policies applied to avoid the occurrence of those failures.

Reliability Analysis of Gas Turbine

This chapter presents the application of reliability concepts to evaluate the overall performance of gas turbine used in open cycle or combined-cycle thermal power plants. The thermodynamics derived performance parameters of gas turbines are presented, including the presentation of the tests codes used to evaluate turbine performance during power plant commissioning. The IEEE Std 762 is presented as traditional way to measure gas turbine availability although it is based on deterministic analysis and does not allow long-term prediction of gas turbine performance. The fundamental reliability and availability concepts associated with gas turbine are presented and an example of reliability analysis of a heavy duty gas turbine is also presented.

Combined-Cycle Gas and Steam Turbine Power Plant Reliability Analysis

The reliability and availability of the combined-cycle thermal power plants depends on the perfect operation of all its systems (e.g. gas turbine, heat recovery steam generator, steam turbine and cooling system). The Heat Recovery Steam Generator (HRSG) is the link between the gas turbine and the steam turbine process having the function of converting the exhaust gas energy of the gas turbine into steam. In the cooling water system, heat removed from the steam turbine exhaust in the condenser is carried by the circulating water to the cooling tower, which rejects the heat to the atmosphere. This chapter presents reliability and availability analysis of a 500 MW combined-cycle thermal power station aiming at defining the most critical components of the main pieces of equipment as for power plant availability. The cooling tower cells are detailed evaluated in order to improve there availability through risk analysis and reliability centered maintenance concepts.

Probabilistic Risk Analysis of a LNG Carrier Loading Pipeline

The loading and unloading operation of a LNG carrier is dependent on the perfect performance of the loading/unloading equipment, such as valves, tanks and pipes. The rupture of a ship pipeline (part of the manifold or other secondary pipes) used for LNG loading or unloading can cause the leakage of the fluid causing not only the complete stop of the loading or unloading operation but also exposing the ship and other terminal facilities to a risk associated with LNG leakage. The paper applies structural reliability concepts to evaluate the probability of failure of a pipeline due to the presence of a crack in the pipe wall. The analysis considers the probability of occurrence of brittle fracture associated with a through thickness crack propagation. The limit state function as for brittle fracture analysis is presented and as for reliability analysis three random variables are considered: material fracture toughness, crack size and pipe thickness. The Monte Carlo simulation method is used to calculate the probability of failure. Based on those results, the paper proposes the use of the cause-consequence diagram to evaluate the accident scenarios associated with the pipe rupture, which failure probability was previously calculated. The events that appear in the diagram are associated with alarm and control systems that are used as monitoring system for loading and unloading operations. Those failure probabilities can be calculated using reliability database. The consequences of each scenario can be defined based on literature review. The main analysis result will be the risk profile associated with a pipe brittle fracture. The method is used for the analysis of a LNG carrier operating in a Brazilian harbor.Copyright

Consequence analysis of a liquefied natural gas floating production storage offloading (lng fpso) leakage

A quantitative risk assessment comprises some basic activities that have to be developed to allow the quantification of the risks involved in the operation of a system or process under analysis. Basically, the likelihood of the undesired events has to be identified as well as their consequences must be calculated. When the risks in the operation of a marine vessel are analyzed, the same process has to be followed. For each specific phase of the marine vessel mission, all of the undesired events must be accurately determined and evaluated. Many different types of undesired events must be investigated, such as: fire, explosion, collision, falling objects and marine hazards. There are many techniques involved in the estimation of the likelihood of the events and the same occurs for the evaluation of their consequences. The purpose of this paper is to study a leakage during a cargo offloading considering a LNG shuttle tanker and a Liquefied Natural Gas Floating Production Storage Offloading (LNG-FPSO) in the Pre Salt Brazilian coast. Once defined the feasible scenarios and the total quantity discharged, the consequences will be evaluated using physical models described in the literature and implemented in commercial softwares. The main idea is to identify all possible consequences and verify their magnitudes. As this is an isolated study, where the likelihood of the event will not be estimated, the final objective is to use the results obtained to predict mitigating measures to the system. This is not a simple task due to the complexity of the phenomena developed after the leakage. In order to verify the extension of possible spread events it is also necessary the identification of many variables, including the atmospheric conditions, the sea condition, the ignition sources, the vessels nearby, the shuttle tanker(s), and the positioning of the vessels involved in the offloading operation.Copyright

Method to select instrumentation for hydraulic turbines in retrofitting process

Almost 83% of the brazilin electric power generation is provided by hydroelectric power stations, most of them built in the 60s or 70s. The increase in the electric energy demand forces the power plants to increase their availability. That increase may be possible through maintenance policy improvement. Another alternative is the hydro generator retrofitting aiming at the extension of operational life, the use of remote operation techniques and the improvement of maintenance policy. This paper presents a method for instrumentation selection during the retrofitting design process aiming at applying predictive maintenance policy as a tool to improve equipment availability. The method is based on the Reliability Centered Maintenance (RCM) concepts to select the most critical components to apply on condition monitoring philosophy. That criticality is defined based on the component failure effects on the hydro generator operational condition. The method is applied on the selection of instrumentation for a Kaplan turbine.

Reliability Analysis in Reciprocating Compressors for Refrigeration Systems

The most-used refrigeration system is the vapor-compression system. In this cycle, the compressor is the most complex and expensive component, especially the reciprocating semihermetic type, which is often used in food product conservation. This component is very sensitive to variations in its operating conditions. If these conditions reach unacceptable levels, failures are practically inevitable. Therefore, maintenance actions should be taken in order to maintain good performance of such compressors and to avoid undesirable stops of the system. To achieve such a goal, one has to evaluate the reliability of the system and/or the components. In this case, reliability means the probability that some equipment cannot perform their requested functions for an established time period, under defined operating conditions. One of the tools used to improve component reliability is the failure mode and effect analysis (FMEA). This paper proposes that the methodology of FMEA be used as a tool to evaluate the main failures found in semihermetic reciprocating compressors used in refrigeration systems. Based on the results, some suggestions for maintenance are addressed.