scholarly journals Oil Tanker Simplified Fatigue Assessment with Inspection and Repair Approach and Parameters

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Ozgur Ozguc
Keyword(s):  
Fatigue Life ◽  
Life Assessment ◽  
Time To Failure ◽  
Maritime Industry ◽  
Safety Level ◽  
Fatigue Assessment ◽  
Hull Structure ◽  
Longitudinal Stiffeners ◽  
Oil Tanker ◽  
Side Shell

The occurrence of cracks in the hull structure of oil tankers is an important concern for the maritime industry because crack propagation will reduce collapse strength of deck-stiffened panels and, consequently, decrease the ultimate hull girder capacity of ship’s structures.  Fatigue is an important design criteria for ships to ensure a sufficiently high safety level. Fatigue life predictions of ship’s structural details have traditionally been carried out using S-N approach and the Palmgren-Miner’s rule. The principal objective of such approach is to estimate the time to failure in order to ensure a satisfactory design lifetime of ship’s structural components. Potential cracks are considered to occur in the side shell, in the connections between longitudinal stiffeners and transverse web frame. The main objectives of the present study are to evaluate the fatigue life of vessel’s amidships using the simplified fatigue method, which is based on DNVGL-CG-0129 “Fatigue Assessment of Ship Structures” in order to determine the main cause of the observed cracks on the single skin oil tanker. Fatigue assessment was based on worldwide trade. Longitudinal stiffeners at transverse frames amidships are considered. The results show that fatigue life is generally above 20 years; however, analysis has revealed that the fatigue life of typical stiffener transitions in the side shell is below 20 years. The fatigue lives of side shell longitudinals are regarded as normal for ships built in the period between 1980 and 1990 with extensive use of high tensile steel in the side shell. Inspection and repair proposals of details with fatigue lives below 20 years are advised accordingly. Findings of fatigue analyses provide remaining life assessment, inspection plan definition, determination of repair and modification solutions, and avoiding integrity issues resulting in production downtime and hot work or dry dock.

A Study on the Fatigue Life Assessment for Urban EMU Structure

2007 ◽  
Vol 345-346 ◽  
pp. 283-286
Author(s):  
Jong Duk Chung ◽  
Jang Sik Pyun ◽  
Ouk Sub Lee
Keyword(s):  
Fatigue Life ◽  
Endurance Limit ◽  
Assessment Method ◽  
Cumulative Damage ◽  
Life Assessment ◽  
Random Load ◽  
Urban Transit ◽  
Fatigue Assessment ◽  
Fatigue Life Assessment ◽  
Approach Method

In these days, most urban railway vehicles have been serviced under the random load application. However, it is considered to be a major factor of safety to predict the fatigue life for structures. It is thus required that fatigue assessment method for cumulative damage approach while Korea domestic regulations practices only the only has endurance limit approach. With this endurance limit approach, fatigue life prediction is impossible. In this research, the fatigue assessment for urban transit structure by using of cumulative damage approach method and related theories are presented.

Fatigue Life Assessment of Single Layer 60512 PVDF Barrier in Unbonded Flexible Risers

2015 ◽  
Author(s):  
Upul S. Fernando ◽  
Michelle Davidson
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Life Assessment ◽  
Dynamic Strain ◽  
Flexible Pipe ◽  
Fatigue Assessment ◽  
Local Plastic ◽  
Fatigue Life Assessment ◽  
Safety Margins ◽  
Local Plastic Strain

The polymeric barrier is one of the key components in a flexible pipe, the sound function of which is essential for the containment of the transported medium, ensuring no leakage to the environment which could result in undesired consequences. According to API 17J the barrier design must be able to sustain certain static and dynamic strain conditions however; the actual design or the fatigue assessment of the barrier is not covered within the standard. Since the barrier is subjected to the same dynamic loading as the pipe the durability and integrity of the barrier is a key issue that needs to be addressed during barrier design for dynamic risers. This paper discusses a fatigue life assessment procedure for a barrier made of copolymer Grade 60512 PVDF. A flexible pipe barrier is manufactured by continuous extrusion of polymer onto a metallic carcass. The carcass has a spiral structure with an irregular outer profile. As such, the extruded polymer on this irregular surface inevitably gives non-uniform thickness and geometric anomalies where the polymer has flowed into gaps in the carcass. During pipe loading such anomalies act as stress concentrations and become critical locations for fatigue crack formation. The evaluation of the effect of the barrier profile shape on the fatigue durability of the barrier is therefore an essential requirement, in particular, in cases where the barrier consists of a single extruded polymer layer. Within the procedure outlined in this paper, the fatigue assessment of the barrier is made using the local plastic strain behaviour. The maximum stress concentration factor and the acceptable profile for the extruded barrier are selected to provide adequate safety margins for the project specific loading conditions. A procedure has been proposed to predict the local plastic strain of the barrier using global service loading data.

scholarly journals Integral treatment of butt joints for the fatigue life assessment in the low cycle fatigue regime

2020 ◽  
Author(s):  
Benjamin Möller
Keyword(s):  
Fatigue Life ◽  
Life Assessment ◽  
Cyclic Behavior ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Butt Joints ◽  
Variable Amplitude Loading ◽  
Fatigue Assessment ◽  
Variable Amplitude ◽  
Integral Treatment

Abstract The framework for a fatigue assessment of welded joints under service loading conditions of crane structures from the low cycle to the high cycle fatigue regime includes the consideration of elastic-plastic material behavior, variable amplitude loading, and acceptable calculation times. Therefore, an integral treatment of butt joints has been developed for fatigue life estimation. The butt weld is considered in its entirety, so that it can be described by its cyclic behavior. The evaluation of the cyclic stress-strain behavior and tri-linear strain-life curves of butt joints for different high-strength, fine-grained structural steels, derived by strain-controlled fatigue tests, is the basis for this description. This procedure is not limited to conventionally applied gas metal arc welding only, but also the fatigue assessment of laser beam welding is possible, for example. Cyclic transient effects have been analyzed and a distinctive cyclic softening is described by linearization of Ramberg-Osgood parameters, depending on the damage content of each cycle derived from constant amplitude, strain-controlled tests. On the basis of the cyclic behavior in combination with memory and Masing behavior, a simulation of the stress-strain paths of investigated butt welds, under constant and variable amplitude loading, has been performed. Damage parameters are used to accumulate the damage cycle by cycle in order to derive the fatigue lifetime. Finally, calculated fatigue lives were compared with experimentally determined lives, showing the impact of this procedure.

Fatigue-Life Assessment

2021 ◽  
pp. 98-133
Author(s):  
Phillip E. Prueter
Keyword(s):  
Fatigue Life ◽  
Damage Tolerance ◽  
Pressure Vessels ◽  
Life Assessment ◽  
Cyclic Plasticity ◽  
Fatigue Assessment ◽  
Fatigue Life Assessment ◽  
Component Design ◽  
Engineering Mechanics ◽  
Growth Approach

Abstract This article offers an overview of fatigue fundamentals, common fatigue terminology, and examples of damage morphology. It presents a summary of relevant engineering mechanics, cyclic plasticity principles, and perspective on the modern design by analysis (DBA) techniques. The article reviews fatigue assessment methods incorporated in international design and post construction codes and standards, with special emphasis on evaluating welds. Specifically, the stress-life approach, the strain-life approach, and the fracture mechanics (crack growth) approach are described. An overview of high-cycle welded fatigue methods, cycle-counting techniques, and a discussion on ratcheting are also offered. A historical synopsis of fatigue technology advancements and commentary on component design and fabrication strategies to mitigate fatigue damage and improve damage tolerance are provided. Finally, the article presents practical fatigue assessment case studies of in-service equipment (pressure vessels) that employ DBA methods.

Fatigue Life Assessment of Aluminium Alloy 6061 Specimen Using Signal Analysis Approach for Automotive Components

2012 ◽  
Vol 165 ◽  
pp. 26-30
Author(s):  
N.A. Azmir ◽  
Shahrum Abdullah ◽  
Mahfodzah M. Padzi
Keyword(s):  
Fatigue Life ◽  
Aluminium Alloy ◽  
Fatigue Damage ◽  
Structural Engineering ◽  
Manufacturing Industry ◽  
Dynamic Responses ◽  
Life Assessment ◽  
Fatigue Assessment ◽  
Damage Prediction ◽  
Data Editing

This paper is aimed to investigate the fatigue assessment of aluminium alloy 6061specimen, one of the widely used aluminium alloys in the production of mechanical components. The alloy possesses the ability of critical failure caused by fatigue when they are subjected to dynamic responses in automotive-type components. The specimens were prepared according to the ASTM E606 and ASTM E1820 standards which were then subjected to two types of cyclic loading amplitude modes namely constant amplitude and random amplitude. The effort is initiated by implementing fatigue data editing approach for random amplitude signal, the conventional method, the finite element method (FEM) and fatigue assessment determination through the statistical method of root mean square (r.m.s) and kurtosis. The input and edited signal acquired will be analyzed for the prediction of the fatigue damage based on the strain model approaches, i.e. Coffin-Manson, Morrow and SWT. From the results obtained, both edited and non-edited signals load display the same amount of fatigue damage to consequently decrease the analysis duration. In addition, the FEM was found to be the best approach for estimating the fatigue life. This research has finally revealed that the higher cyclic load amplitude will only diminish the fatigue life of a specimen. Furthermore, this fatigue assessment study will look forward to improve structural engineering development in monitoring components and consequently access the damage prediction variable which could later be implemented to the manufacturing industry.

Methodology for Time Domain Fatigue Life Assessment of Risers and Umbilicals

2010 ◽  
Author(s):  
Oddrun Steinkjer ◽  
Nils So̸dahl ◽  
Guttorm Gryto̸yr
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Time Domain ◽  
Life Assessment ◽  
Statistical Uncertainty ◽  
Short Term ◽  
Fatigue Assessment ◽  
Fatigue Life Assessment ◽  
Non Linear ◽  
Selection Of

Risers and umbilicals are exposed to dynamic loading from waves and floater motions. These structures are known to have a pronounced non-linear response characteristic. Non-linear time-domain finite element analyses is in general required to give an adequate description of the non-linearities involved. Analyses of a large number of short-term environmental conditions considering stochastic wave loading are required to give a representative description of the long-term fatigue loading on the structure. Short term fatigue damage is established by means of rain-flow cycle (RFC) counting in each stationary short-term condition. It is has been experienced that significant statistical uncertainties can be present in the short-term fatigue damage estimates. This is because the accumulated fatigue damage in a stationary condition normally has significant contribution from the largest stress cycles in the realisation. Selection of proper simulation length is hence essential to obtain reliable fatigue life estimates. Applicable codes and standards for risers and umbilicals provide Design Fatigue Factors (DFF) to secure adequate safety against failure due to wave induced fatigue. The total uncertainty in the calculated fatigue damage comes from various sources and the DFFs in e.g. DNV-OS-F201 “Dynamic Risers” and API-RP-2RD corresponds to a certain uncertainty level in the fatigue damage estimate. A recommended target value for the statistical uncertainty of the fatigue damage estimates is given with basis in these design codes. The objective of this paper is to give a description of a methodology recommended for time domain fatigue assessment. Special focus will be on the importance of adequate simulation time for predicting the short-term fatigue damage and selection of the short-term seastates in the scatter diagram. Statistical uncertainty is one source that the analyst actually can influence by selecting proper analysis methodology. A statistical uncertainty meassure can be used to evaluate the robustness in the estimated fatigue life. Assessment of statistical uncertainty in fatigue damage estimate is demonstrated by case studies. The fatigue assessment methodology discussed in this paper, will be described in an update of DNV-RP-F204 “Riser Fatigue” 2010.

Fatigue Reliability of Maintained Welded Joints in the Side Shell of Tankers

1998 ◽  
Vol 120 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Y. Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Crack Growth ◽  
Fatigue Reliability ◽  
Linear Elastic ◽  
Transverse Pressure ◽  
Section Area ◽  
Hull Structure ◽  
Longitudinal Stiffeners ◽  
Longitudinal Bending ◽  
Elastic Fracture ◽  
Side Shell

A formulation is presented for the assessment of the reliability of a local ship hull structure regarding fatigue failure. The potential cracks are considered to occur in the side shell, in the connections between longitudinal stiffeners and transverse web frame. The analysis is performed for T-shaped stiffeners. The model accounts for the crack growth process applying linear elastic fracture mechanics. The long-term stress range acting on the elements is defined as a function of the local transverse pressure of internal cargo and outside water, combined with the stresses resulting from the longitudinal bending of the hull. The global hull loading is a combination of horizontal and vertical bending moments. The present paper analyzes the importance of including the transverse pressure loading for the process of the crack growth and also the distribution of the net section area of midship and location of stiffeners. The formulation has been applied to a tanker. The fatigue reliability is predicted by a time variant formulation and the effects of maintenance actions in updating the reliability assessment are shown.

Proposal for an Improved Engineering Fatigue Lifetime Assessment Concept

2016 ◽  
Author(s):  
Jürgen Rudolph ◽  
Paul Wilhelm ◽  
Armin Roth ◽  
Matthias Herbst ◽  
Matthias C. Kammerer ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Influencing Factors ◽  
Experimental Results ◽  
Life Assessment ◽  
Experimental Program ◽  
Materials Testing ◽  
Assessment Procedure ◽  
Fatigue Lifetime ◽  
Fatigue Assessment ◽  
Fatigue Life Assessment

Fatigue life assessment for pressurized components in nuclear power plants (NPPs) is an essential part of the aging management (AM) ensuring safe and long term operation (LTO). For fatigue life assessment different codes and standards provide a variety of methodologies with variable complexity. Major fatigue life influencing factors such as temperature, surface finish, multiaxiality, loading history and others are often considered in a more or less global way by combined overall reduction factors covering multiple mechanisms together. Other effects such as the environment or hold times are often considered not at all or otherwise with high levels of conservatism resulting in large discrepancies between calculated fatigue life and practical experience from power plant operation. In order to reduce this inadequacy a more accurate fatigue lifetime assessment concept including individual fatigue life influencing factors in a mechanistic manner is required. Nevertheless, these amendments are to fit into the existing basic engineering approach of design against fatigue failure as it is implemented in nuclear standards and design codes. In the framework of an ongoing three years German cooperation R&D project with participation of the Materials Testing Institute MPA University of Stuttgart and AREVA GmbH (Erlangen) it is the aim to both improve the state of the art based on an experimental program for some of the main fatigue life influencing factors and on the derivation of a practicable engineering fatigue assessment procedure. Within this fatigue assessment procedure the dominant fatigue life influencing factors are considered individually. The experimental program covers fatigue test results for austenitic and ferritic piping materials including a dissimilar metal weld. Within the testing program strain controlled fatigue tests were performed with and without hold-times in air and high temperature water environments. Smooth and notched specimens provide a database to study the influence of notches and multiaxiality. These results are used to state on the applicability of commonly used failure hypothesis like von Mises and Tresca in comparison to advanced fatigue damage parameters. In addition to constant amplitude strain controlled fatigue testing load spectra were investigated. Thereby fatigue cumulative damage models like Miner’s rule can be evaluated. This publication constitutes a follow-up to a previous paper [1] and targets at the presentation of experimental results in conjunction with potentials with an improved fatigue assessment concept. In addition the methodology of the concept is applied to experimental results on fatigue life assessments for piping materials published by other organizations. Requirements for further experimental investigations towards the verification of a closed concept are formulated.

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