Integrity Assessment of Interaction of Dents With Residual Stresses of Welds Using Probabilistic Design Analysis

2012 ◽  
Author(s):  
Husain Mohammed Al-Muslim ◽  
A. F. M. Arif
Keyword(s):  
Residual Stresses ◽  
Weld Line ◽  
Design Analysis ◽  
Probabilistic Design ◽  
Stress Range ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Girth Welds ◽  
Longitudinal Welds ◽  
The Impact

The interaction of dent with the weld has always been considered a threat to the pipeline. Therefore, Codes and procedure impose more stringent rules than normally applied to plain dents. For example, ASME B31.8 considers dents deeper than 2% and interacting with welds to be injurious and requires an engineering assessment if they are to be left without repair. The objective of this paper is to present a new method of assessment that utilizes finite element analysis couples with probabilistic design analysis. In this paper, the impact of interaction of dent with longitudinal welds and girth welds will be under static and cyclic pressure conditions will be evaluated. The combined effects are included in a single FEA model and the welds will be simulated by imposing initial residual stresses along the weld line. The first part of the paper uses deterministic analysis to present strain and stress contours at the end of indentation stage as well as the stress range and fatigue cycles at the end of pressure cycle stage for a longitudinal weld case as well as girth weld case. The second part uses probabilistic design analysis with variable geometry, material and pressure in addition to the weld location and residual stress value to determine the sensitivity of the strain, stress, and stress range to the input. Two probabilistic design analyses are conducted: one for the interaction of dent with longitudinal welds, the other for the interaction of dent with girth welds.

Comparison of Plastic Collapse Solutions for Surface Breaking Flaws in Standard Assessment Procedures With FEA

2013 ◽  
Author(s):  
Rajil Saraswat ◽  
Ali Mirzaee-Sisan
Keyword(s):  
High Fracture Toughness ◽  
Plastic Collapse ◽  
High Fracture ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Standard Assessment ◽  
Definition Of ◽  
Girth Welds ◽  
Assessment Procedures ◽  
The Impact

Engineering Critical Assessment (ECA) procedures generally use the Failure Assessment Diagram (FAD) concept for integrity assessment of components containing flaws. An FAD assessment is described by Kr and Lr values, where Kr reflects the toughness of the material while Lr measures the proximity to plastic collapse. Nowadays pipeline girth welds generally have high fracture toughness (Kmat) and it can be argued that plastic collapse is the governing failure mode. The definition of plastic collapse can affect the determination of the Lr parameter and should be carefully chosen. In the present work finite element analysis has been carried out to evaluate the collapse load under local collapse and global collapse conditions. These have been compared with the solutions available in the BS7910 and R6 procedures and the differences have been highlighted. The impact of the choice of plastic collapse solution on the crack driving force has been analysed.

Weld-Overlay Analyses: An Investigation of the Effect of Weld Sequencing

2008 ◽  
Author(s):  
T. Zhang ◽  
G. Wilkowski ◽  
D. Rudland ◽  
F. Brust ◽  
H. S. Mehta ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Nuclear Reactor ◽  
Internal Cooling ◽  
Element Analysis ◽  
Weld Overlay ◽  
Weld Material ◽  
Diameter Pipe ◽  
Pipe Joints ◽  
Girth Welds

The weld overlay process has been developed and applied to repair of nuclear reactor pipe girth welds for many years in BWR plants. The objectives of such repairs were to induce compressive axial residual stresses on the pipe inside surface, as well as increase the pipe thickness with a weld material that is not susceptible to stress-corrosion cracking. Hence, understanding the residual stress distribution is important to evaluate the reliability of pipe joints with weld overlay repairs. In this paper, a six-inch diameter Schedule 120 stainless steel pipe with an overlay thickness of 7.87 mm (0.31 inch) was picked as a validation case. Weld sequencing effects were thoroughly studied. The residual stresses were calculated by using thermal elasto-plastic finite-element analysis (FEA). After comparing results using different weld sequences, it was found that the calculated weld residual stresses on ID surface were very sensitive to weld sequencing in FE analyses as well as internal cooling rate. The influence of the weld sequencing was relatively secondary to the pipe distortion. An optimum (producing compressive residual stress on the ID surface) weld sequencing was obtained and applied to a 711.2 mm (28-inch) diameter pipe-to-elbow girth weld with an overlay thickness of 24.9 mm (0.98 inch) and a pipe thickness of 29.5 mm (1.16 inch).

The Validation of Weld Residual Stresses for Use in Structural Integrity Assessment

2011 ◽  
Vol 70 ◽  
pp. 297-302 ◽  
Author(s):  
Steve K. Bate ◽  
P. John Bouchard
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Measurement Techniques ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Modelling Techniques ◽  
High Level ◽  
Assessment Procedures

The continued safe and reliable operation of plant invariably has to consider the assessment of defects in welded structural components. This requires some estimate of the residual stresses that have developed during the welding fabrication process. For as-welded structures these stresses can be of yield magnitude. Engineering critical assessment procedures such as R6, BS 7910, FITNET and API 579-1 provide simplified estimates, bounding profiles or advice on detailed analysis or measurement which can be applied to provide conservative estimates of the remaining life of plant. The use of finite element analysis (FEA) is being applied more frequently to predict residual stresses in welded components for assessment purposes. This calculation involves complex non-linear analyses with many assumptions. As a consequence, the accuracy and reliability of solutions is variable. In order to improve the consistency of weld modelling, and hence the accuracy and confidence in their use, a set of Guidelines covering the calculation of residual stresses have been developed. The residual stress calculations need to be validated before the results can be used in assessments and guidance on how to demonstrate the required standard of validation proof is provided with these Guidelines. The level of validation required, depends on the problem being solved and the sensitivity of the assessment to the presence of residual stress. For example a high level of validation may be required for assessments of safety critical plant. To support these calculations, measurements are required and a series of ‘Weld Residual Stress Benchmarks’, describing welded mock-ups which have been measured using various measurement techniques, are being collated which the users can then refer to when validating their finite element modelling techniques and thus provide a greater confidence in the predicted results.

Residual Stresses in Strength Mismatched Welded Pipes

2017 ◽  
Author(s):  
Ali Mirzaee-Sisan ◽  
Junkan Wang
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Thermal Stresses ◽  
Structural Integrity ◽  
Welding Residual Stress ◽  
Temperature Fields ◽  
Transient Temperature ◽  
Element Analysis ◽  
Girth Welds ◽  
Welded Pipe

It is commonly understood that residual stresses can have significant effects on structural integrity. The extent of such influence varies and is affected by material properties, manufacturing methods and thermal history. Welded components such as pipelines are subject to complex transient temperature fields and associated thermal stresses near the welded regions. These thermal stresses are often high in magnitude and could cause localized yielding around the deposited weld metal. Because of differential thermal expansion/contraction episodes, misfits are introduced into the welded regions which in turn generate residual stresses when the structure has cooled to ambient temperature. This paper is based on a recently completed Joint Industry Project (JIP) led by DNV GL. It briefly reviews published experimental and numerical studies on residual stresses and strength-mismatched girth welds in pipelines. Several Finite Element Analysis (FEA) models of a reeling simulation have been developed including mapping an initial axial residual stress (transverse to the weld) profile onto a seamless girth-welded pipe. The initial welding residual stress distribution used for mapping was measured along the circumference of the girth welds. The predicted residual stresses after reeling simulation was subsequently compared with experimental measurements.

Estimation of Elastic Follow-Up in Structures

2011 ◽  
Vol 462-463 ◽  
pp. 361-365 ◽  
Author(s):  
Saeid Hadidi-Moud ◽  
David John Smith
Keyword(s):  
Residual Stresses ◽  
Closed Form ◽  
Analytical Solutions ◽  
Unified Framework ◽  
Integrity Assessment ◽  
The Impact ◽  
Model Structures

Using simplified benchmark models, representative of the behavior of real structures, a unified framework for quantification of elastic follow-up (EFU) in structures has been provided. Closed form analytical solutions for evaluation of elastic follow-up are presented for model structures. The impact of elastic follow-up on the relaxation i.e. the redistribution of residual stresses has been explored and hence its significance in the integrity assessment of structures in general and in classification of residual stresses in particular has been highlighted.

Finite Element Analysis of the Effect of Oil Jet Peening Process in a Material

2009 ◽  
Author(s):  
A. Sahaya Grinspon ◽  
R. Gnanamoorthy
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Residual Stresses ◽  
Element Analysis ◽  
Stress Components ◽  
Modification Technique ◽  
Loading And Unloading ◽  
Oil Jet ◽  
The Impact

Oil peening is a new surface modification technique developed to introduce compressive residual stresses in metallic components. The magnitude and distribution of residual stresses and plastic strain in the oil peened AA6061-T4 alloy was evaluated using finite element method (FEM). The simulation of single drop impact against a plastically deformable material was performed. The contours of stress components are presented to show the formation of residual stress distribution. Finite element analysis reveals that the stress and strain patterns around the impact region of an oil drop during loading and unloading with different impact pressures. Impact pressure significantly influences the axial displacement, residual pileup and residual stress.

The Importance of Residual Stresses in Microelectronic Products and Materials

2006 ◽  
Vol 524-525 ◽  
pp. 1-10
Author(s):  
Wolfgang H. Müller
Keyword(s):  
Residual Stresses ◽  
Diffusion Processes ◽  
Organic Substrates ◽  
Element Analysis ◽  
Solder Interconnects ◽  
Theoretical Predictions ◽  
Board Material ◽  
Materials Used ◽  
Microelectronic Components ◽  
The Impact

In this paper we will discuss the impact of residual stresses on the reliability of microelectronic components and the materials used therein. The following issues will be particularly emphasized: First, the tendency toward delamination and subsequent cracking along interfaces, such as between silicon dies, organic substrates, glues, and underfill material; second, the fatigue of electrolytically deposited copper vias within the substrate and FR4 board material; third, the accumulation of irreversibly accumulated plastic (creep) strain in lead containing as well as leadfree solders; the microstructural change observed during thermo-mechanical use within the bulk as well as at the interface of solder interconnects. We will present state-of-the-art numerical techniques that allow to quantify the development of stresses and strains within the aforementioned materials, mostly by finite element analysis, as well as the coupling between local stresses and diffusion processes, which is theoretically based on phase field models. Further emphasis is put on proper knowledge and determination of the inherent material parameters and how theoretical predictions can be linked to and validated by experimental observations and facts.

Effects of High-Low Misalignment on Girth Weld Integrity

2014 ◽  
Author(s):  
Yong-Yi Wang ◽  
Kunal Kotian ◽  
Steve Rapp
Keyword(s):  
Load Capacity ◽  
Weld Strength ◽  
Contributing Factors ◽  
Element Analysis ◽  
Absolute Level ◽  
Service Failures ◽  
Weld Profile ◽  
Circumferential Extent ◽  
Girth Welds ◽  
The Impact

High levels of high-low misalignment in pipeline girth welds have been identified as one of the possible contributing factors to some of the recent pre-service hydrostatic test failures or subsequent service failures. However, pipeline service experience indicates that nominally defect-free girth welds with high levels of misalignment and proper weld profiles can provide satisfactory long-term service. In this paper, recent analytical and experimental work aimed at understanding the impact of high-low misalignment in girth welds is described. In nominally defect-free welds, the performance of the welds is found to be predominantly determined by the misalignment ratio, weld strength mismatch ratio, and the weld profile. Iso-load-capacity relations are developed through finite element analysis (FEA) to capture the interdependence of those key parameters. The analysis procedure is validated by cross-weld tensile testing of girth welds with various levels of misalignment and weld strength mismatch. The effects of the circumferential extent of misalignment, alternatively termed local misalignment, are also analyzed. The effects of misalignment in girth weld with planar flaws are examined in the context of the tensile strain capacity. The analytical and experimental evidence indicate that the absolute level of misalignment is not a sole indicator of girth weld performance. Weld transition profile, pipe wall thickness, and weld strength mismatch all play an important role. With proper weld profiles, minimal or small reduction of load capacity is observed even at very high levels of misalignment. Work is continuing to further examine the effects of high-low misalignment with a goal of making practical recommendations to be included in codes and standards.

Structural Integrity of a Spar in Collision With a Large Supply Vessel

2013 ◽  
Author(s):  
Xinguo Ning ◽  
Bob L. Zhang ◽  
Sudhakar Tallavajhula
Keyword(s):  
Kinetic Energy ◽  
Structural Integrity ◽  
Impact Force ◽  
High Energy ◽  
Progressive Damage ◽  
Element Analysis ◽  
Impact Speed ◽  
Integrity Assessment ◽  
Damage Models ◽  
The Impact

The objectives of this study are to establish numerical approaches to evaluate the structural integrity of a generic Spar hull in collision with a large supply vessel and to reveal its progressive collision damage characteristics. Dynamic and nonlinear finite element analysis is implemented using ABAQUS/Explicit module [1] respectively for two collision scenarios. One is a realistic simulation where the impact kinetic energy governed by an initial impact speed and total mass of a ship is gradually depleted during the collision. The other is a simplified analytical method where the impact speed of a ship bow throughout the collision is constant or the total impact energy is unlimited. With a combination of calibrated material progressive damage models and Mises plasticity, progressive collision damages of the hull structures are accurately captured for structural integrity assessment. The collision energy absorption characteristics, the impact force-deformation curves, the progressive damage modes and the correlation between the impact force, kinetic energy and damages are revealed. Based on numerical investigation, the two analytical scenarios are compared and the implication for the design analysis is elucidated. As a complementary to the ABS code [2], the alternative collision damage criterion in ABS MODU [3] applicable to column-stabilized units is justified to be applicable to a Spar subjected to high-energy impact.

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