Construction of Various Fatigue Design Master S-N Curves for Offshore/Marine Structures Using Battelle Structural Stress Method

2011 ◽  
Author(s):  
Jeong K. Hong
Keyword(s):  
Structural Integrity ◽  
Environmental Safety ◽  
Fatigue Tests ◽  
Structural Stress ◽  
Stress Concentrations ◽  
Marine Structures ◽  
Fatigue Design ◽  
Weld Toe ◽  
Weld Fatigue ◽  
Corrosive Environments

Reliable structural integrity evaluation is a critical part of the design process. Reliable structural integrity evaluation is especially important for large and complex structures such as buildings and offshore/marine installations that have significant implications for human and environmental safety. The design and careful evaluation of welded structures are essential in structural design since the stress concentrations at the welds have significant impact on the overall fatigue lives of the structures. A mesh-insensitive structural stress method has been developed and proven to be highly effective in correlating fatigue behaviors of welded joints by Battelle researchers. The Battelle structural stress method and related weld fatigue master S-N curve approach has been adopted by ASME and API in 2007 [1–2]. The design fatigue master S-N curve has been constructed by incorporating the results of more than 800 fatigue tests, which are clearly categorized as weld toe failure. In addition, a design master S-N curve for weld root failure has been constructed recently [3]. For offshore/marine structures, it is essential to consider weld fatigue damage in corrosive environments as well as that in air, and to understand the effects of techniques commonly applied to improve weld fatigue strength of the structures, e.g., hammer peening, toe grinding, and TIG dressing. In order to meet the industry’s increasing demand for reliably, fatigue resistant structures, design master S-N curves incorporating the effects of corrosive environments and weld improvement techniques have been constructed. These new curves are based on existing weld fatigue data from the literature and class bodies’ fatigue design documents.

A Robust Structural Stress Method for Fatigue Analysis of Offshore/Marine Structures

2005 ◽  
Vol 127 (1) ◽  
pp. 68-74 ◽  
Author(s):  
P. Dong
Keyword(s):  
Finite Element ◽  
Fatigue Behavior ◽  
Fatigue Analysis ◽  
Finite Element Mesh ◽  
Complex Structures ◽  
Structural Stress ◽  
Marine Structures ◽  
Element Mesh ◽  
Fatigue Design ◽  
Structural Stresses

Recent rapid advances in developing mesh-insensitive structural stress methods are summarized in this paper. The new structural stress methods have been demonstrated to be effective in reliably calculating structural stresses that can be correlated with fatigue behavior from simple weld details to complex structures. As a result, a master S–N curve approach has been developed and validated by a large amount of weld S–N data in the literature. The applications of the present structural stress methods in a number of joint types in offshore/marine structures will be illustrated in this paper. The implications on future applications in drastically simplifying fatigue design and evaluation for offshore/marine structures will also be discussed, particularly for using very coarse finite element mesh designs in ship structures.

A Robust Structural Stress Method for Fatigue Analysis of Ship Structures

2003 ◽  
Author(s):  
P. Dong
Keyword(s):  
Finite Element ◽  
Fatigue Behavior ◽  
Finite Element Mesh ◽  
Complex Structures ◽  
Structural Stress ◽  
Marine Structures ◽  
Ship Structures ◽  
Element Mesh ◽  
Fatigue Design ◽  
Structural Stresses

Recent rapid advances in developing mesh-insensitive structural stress methods are summarized in this paper. The new structural stress methods have been demonstrated to be effective in reliably calculating structural stresses that can be correlated with fatigue behavior from simple weld details to complex structures. As a result, a master S-N curve approach has been developed and validated by a large amount weld S-N data in the literature. The applications of the present structural stress methods in a number of joint types in offshore/marine structures will be illustrated in this paper. The implications on future applications in drastically simplifying fatigue design and evaluation for offshore/marine structures will also be discussed, particularly for using very coarse finite element mesh designs in ship structures.

Study on Weld Fatigue Evaluation Under Sour Service Environment Using Battelle Structural Stress Method

2013 ◽  
Author(s):  
Jeong K. Hong ◽  
Thomas P. Forte
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Fatigue Behavior ◽  
Structural Stress ◽  
Loading Conditions ◽  
Test Results ◽  
Knock Down ◽  
Weld Toe ◽  
Weld Fatigue ◽  
Sour Service

Risers, pipelines and flowlines for deep water applications are subject to corrosive environments. Especially, in the presence of hydrogen sulfide which makes the field sour, their fatigue performance becomes significantly degraded. In order to quantify the sour degradation effect, a knock-down factor has been introduced. This factor is defined as the fatigue life reduction relative to the in-air fatigue life. Several sets of fatigue test results in sour service environments have been published. These include strip specimens of different sizes, e.g., diameters, wall thicknesses, and arc lengths. Naturally, the knock-down factor must be based upon a statistically valid number of fatigue test results obtained from the same specimen geometry and the same loading conditions tested in air and in sour conditions. Currently, the database available in the open literature is too limited to properly define a knock-down factor. Moreover, there is a great deal of scatter within the database and each test in a sour environment is costly and time consuming. Thus, it is difficult to establish a statistically valid database upon which to base the knock-down factor. A mesh-insensitive structural stress method has been developed by Battelle researchers and has been proven to be highly effective in correlating the fatigue behavior of welded joints. In 2007, the Battelle structural stress based weld fatigue master S-N curve was included in ASME Section VIII Div. 2 because it successfully consolidated more than 800 fatigue test results for weld toe failures onto a single master S-N curve with very little scatter, regardless of specimen shape, size, loading type, and steel alloy [1–2]. A knock-down factor is derived by applying the Battelle structural stress method to the existing database for sour environment tests and by using the current in-air database as the reference condition. This approach will reduce the uncertainty in the knock-down factor because it allows a wider range of sour environment data from specimens of different sizes, types, and loading conditions to be combined, while simultaneously reducing scatter. As such, a unified knock-down factor can be determined with greater statistical validity and wider applicability for design recommendations in sour conditions.

Local strain for fatigue strength of welded structures

2001 ◽  
Vol 36 (6) ◽  
pp. 605-610 ◽  
Author(s):  
V Dattoma ◽  
C Pappalettere
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Structural Integrity ◽  
Strain Curve ◽  
Local Strain ◽  
Fatigue Design ◽  
Curve Versus ◽  
Weld Toe ◽  
Stress Ratios ◽  
Tip Radius

Field criteria, which are usually applied in fracture mechanics to ensure the structural integrity of cracked components, are extended to the fatigue design of welded joints, whose weld toe can be assimilated to a notch with a small tip radius. In particular, fatigue strength in terms of strain rather than of stress has been determined by applying stress cycles with different stress ratios R = σmin/σmax. Finally, for the evaluation of the fatigue strength of welded joints in structural steel, a strain curve versus different R ratios is given to be compared with the service measured local strain at the weld toe.

Effect of Creep on the Residual Stresses in Tube-to-Tubesheet Joints

2010 ◽  
Author(s):  
Nor Eddine Laghzale ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Contact Pressure ◽  
Analytical Model ◽  
Nuclear Power ◽  
Structural Integrity ◽  
Environmental Safety ◽  
Maintenance Cost ◽  
Joint Interface ◽  
Plant Safety ◽  
Material Creep ◽  
Nuclear Power Plant Safety

Steam generators are the subject of major concern in nuclear power plant safety. Within these generators, in addition to the structural integrity, the gross tightness barrier, which separates the primary and secondary circuits, is primarily ensured by the presence of a residual contact pressure at the tube-to-tubesheet joint interface. Any leakage is unacceptable, and its consequences are very heavy in terms of the human and environmental safety as well as maintenance cost. Some studies have been conducted to understand the main reasons for such a failure. However, no analytical model able to predict the attenuation of the residual contact pressure under the effect of material creep relaxation behavior. The development of a simple analytical model able to predict the change of the residual contact pressure as a function of time is laid out in this paper. The results from the analytical model are checked and compared with those of finite elements.

Hull Deformation Effect on Membrane-Type LNG Containment Systems

2016 ◽  
Author(s):  
Bo Wang ◽  
Yung-Sup Shin ◽  
Eric Norris
Keyword(s):  
Structural Integrity ◽  
Water Pressure ◽  
Local Deformation ◽  
Fatigue Tests ◽  
Wave Loads ◽  
Insulation System ◽  
Structural Fatigue ◽  
Hull Structure ◽  
Membrane Type ◽  
Global Deformation

The objective of this study is to investigate the relationship between the maximum allowable hull deformation, which includes global elongation and local deflection, and the capacity of the CCS in membrane-type LNG vessels. The LNG CCS mainly consists of the primary barrier (e.g. a corrugated membrane for GTT MK III system and an invar membrane for GTT NO 96 system) and the insulation panel which is attached to the inner hull through mastics or couplers. The excessive hull elongation due to dynamic wave loads may cause fatigue damage of the primary barrier. Thus, the maximum allowable hull elongation (global deformation) can be determined based on the fatigue strength of the primary barrier. On the other hand, the excessive hull deflection due to cargo or ballast water pressure may cause failure of the insulation panel and the mastic. Therefore, the maximum allowable hull deflection (local deformation) in the hull design can be determined based on the strength of the insulation panel and the mastic. In the present paper, the determination of fatigue life vs. strain curves of materials has been summarized for the primary barrier. Fatigue curves based on either structural fatigue tests or standard specimen tests can be applied in fatigue assessment of a primary barrier. As an example, the finite element (FE) analysis has been conducted on the MK III CCS with the hull structure under pressure loads. Two different load cases including full load and ballast load conditions have been considered to evaluate the structural integrity of the insulation system in numerical simulations. FE results show that the mechanical behavior of the insulation system and the mastic under the maximum allowable hull deflection has been examined based on the yielding strength of each individual component. Finally, the complete procedure to determine the maximum allowable hull elongation and the maximum allowable hull deflection has been developed for meeting the requirements of containment system design for membrane-type LNG carriers.

Effect of Different Welded Structures on Mechanical Properties of TA2 Tube-to-Tubesheet Joints

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Xinlong Wei ◽  
Yang Qian ◽  
Junhui Wang ◽  
Jianxin Zhou ◽  
Xiang Ling
Keyword(s):  
Applied Load ◽  
Low Cycle Fatigue ◽  
Weld Zone ◽  
Steel Tube ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Welded Structures ◽  
Pull Out ◽  
Weld Toe ◽  
Welded Tube

Four types of TA2 welded tube-to-tubesheet joints prepared by manual tungsten arc argon-shielded welding technique are studied in this paper. The pull-out tests and low cycle fatigue tests were performed to optimize welded structures of tube and tubesheet. The results show that fractures of welded TA2 tube and tubesheet samples occur at weld zone of TA2 steel tube for the pull-out tests and low cycle fatigue tests. The extension-tubesheet welded joints have the maximum pull-out forces and the best fatigue resistance, and the internal-bore welded joint with 45 deg bevel occupies second place. Fractures are both initiated from weld toe of the outside of tube for the pull-out tests and low cycle fatigue tests. Crack propagates along the direction of 45 deg for the pull-out test. However, crack propagates perpendicularly to the direction of the applied load for low cycle fatigue test, and then fractures immediately parallel to the direction of the applied load. Fatigue striations with a spacing of about 10 μm can be observed on the fatigue crack propagation zone. However, hemispheroidal dimples exist on instant rupture zone.

scholarly journals Environmental degradation of composites for marine structures: new materials and new applications

2016 ◽  
Vol 374 (2071) ◽  
pp. 20150272 ◽  
Author(s):  
Peter Davies
Keyword(s):  
Composite Materials ◽  
Test Data ◽  
Environmental Degradation ◽  
Structural Integrity ◽  
Mechanical Test ◽  
Traditional Approach ◽  
Essential Element ◽  
Structural Testing ◽  
Marine Structures

This paper describes the influence of seawater ageing on composites used in a range of marine structures, from boats to tidal turbines. Accounting for environmental degradation is an essential element in the multi-scale modelling of composite materials but it requires reliable test data input. The traditional approach to account for ageing effects, based on testing samples after immersion for different periods, is evolving towards coupled studies involving strong interactions between water diffusion and mechanical loading. These can provide a more realistic estimation of long-term behaviour but still require some form of acceleration if useful data, for 20 year lifetimes or more, are to be obtained in a reasonable time. In order to validate extrapolations from short to long times, it is essential to understand the degradation mechanisms, so both physico-chemical and mechanical test data are required. Examples of results from some current studies on more environmentally friendly materials including bio-sourced composites will be described first. Then a case study for renewable marine energy applications will be discussed. In both cases, studies were performed first on coupons at the material level, then during structural testing and analysis of large components, in order to evaluate their long-term behaviour. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

scholarly journals PWR Effect on Crack Initiation Under Equi-Biaxial Loading Development of the Experiment

2016 ◽  
Author(s):  
G. Perez ◽  
C. Gourdin ◽  
S. Courtin ◽  
J. C. Le Roux
Keyword(s):  
Biaxial Loading ◽  
Austenitic Stainless Steels ◽  
Fatigue Curve ◽  
Structural Effect ◽  
Fatigue Tests ◽  
Fatigue Lifetime ◽  
New Device ◽  
Fatigue Design ◽  
Penalty Factor ◽  
Mean Strain

Fatigue lifetime assessment is essential in the design of structures. Under-estimated lifetime predictions may generate overly conservative usage factor values and hence result in unnecessary in-service inspections. In the framework of upgrading the fatigue design rules (RCC-M, RCC-MRx), the uniaxial reference fatigue curve was altered by taking into account effects like: Multiaxiality, Mean stress or strain, Surface roughness (polished or ground), Scale effect, Loading History... In addition to this effect, Environmentally Assisted Fatigue is also receiving nowadays an increased level of attention. To formally integrate these effects, some international codes have already proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The aim of this paper is to present a new device “FABIME2E” developed in the LISN in collaboration with EDF and AREVA. These new tests allow quantifying accurately the effect of PWR environment on semi-structure specimen. This new device combines the structural effect like equibiaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.

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