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.

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.

Limit Plastic Collapse on Remaining Ligament of Flawed Welds for ECA Application

2014 ◽  
Author(s):  
Antonio Carlucci ◽  
Kamel Mcirdi
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Mechanical Strain ◽  
Plastic Collapse ◽  
Fracture Toughness Test ◽  
Element Analysis ◽  
Critical Fracture ◽  
Failure Assessment ◽  
The One ◽  
Girth Welds

Engineering Critical Assessments (ECAs) are routinely used to provide defect acceptance criteria for pipelines girth welds. The Failure Assessment Diagram (FAD) concept is the most widely used methodology for elastic-plastic fracture mechanics analysis of structural components and adopted by standards/documents including BS7910 [1], API579-1/ASME FFS-1 [2], R6 [3]. It is defined by two criterion Kr and Lr which describe the interaction between brittle fracture and fully ductile rupture: Kr measures the proximity to brittle fracture whereas Lr reflects the closeness to plastic collapse. The BS7910 FAD level 2B is the most employed for assessment of flaws under mechanical strain lower than 0.4%, the FAD associated is material-specific and it based on single toughness value obtained from CTOD test, the latter-on gives no information about the tearing initiation. The objective of this paper is to propose an approach for determination of the critical fracture toughness (associated to zero-tearing: JΔa=0). This approach is based on the comparison between the load-CMOD curve provided from a fracture toughness test to the one obtained by Finite Element Analysis (FEA). The goals is to propose a conservative guidance on how to identify a remote strain level below which it may be considered guaranteed the integrity of the remaining ligament.

Fracture Toughness of X-60/Alloy 625 Welded Joints

2005 ◽  
Author(s):  
Alexandre M. Pope ◽  
Marcelo P. Paes ◽  
Jose´ Claudio G. Teixeira
Keyword(s):  
Fracture Toughness ◽  
Filler Metal ◽  
Petroleum Industry ◽  
High Fracture Toughness ◽  
High Fracture ◽  
Dissimilar Joints ◽  
Ni Alloy ◽  
Steel Catenary Risers ◽  
Girth Welds ◽  
Fatigue Failures

Line pipes internally clad by nickel alloy are being considered as steel catenary risers when exploitation of corrosive oils is envisaged and corrosion-fatigue failures are possible. The presence of the Ni alloy as internal clad requires a matching filler metal and, consequently, the girth welds are dissimilar joints. Although these types of welds are widely used in the petroleum industry their fracture toughness are not well documented. Of particular concern is the formation of hard zones in HAZ which are usually associated with low fracture toughness. Joints of API X-60 pipes welded using NiCrMo-3 consumables were CTOD tested at 0°C. Results consistently revealed high fracture toughness values for the weld metal. The HAZ-FL, on the other hand, presented lower values and they were significantly dispersed. Microstructural and fractographic analyses revealed that low values of toughness are associated with local brittle zones (LBZ) mainly IRCGHAZ. The fracture of the specimen that presented the lowest toughness initiated in a partially mixed zone containing hard martensite.

Study on Plastic Collapse Load of Steel Elliptical Heads Under Internal Pressure

2013 ◽  
Author(s):  
Liang Sun ◽  
Guide Deng ◽  
Jiufeng Zhao
Keyword(s):  
Internal Pressure ◽  
Major Axis ◽  
Pressure Vessels ◽  
Outer Diameter ◽  
Maximum Relative Error ◽  
Plastic Collapse ◽  
Collapse Load ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Perfectly Plastic

A general formula for plastic collapse load of elliptical heads under internal pressure is useful in plastic collapse design and integrity assessment of pressure vessels. Plastic collapse load of steel elliptical heads with different shapes and thickness was computed by finite element analysis using elastic-perfectly plastic constitutive model, and a formula with maximum relative error less than 6% was derived from the numerical results. The formula is a function of the yield strength of materials, the ratio of major axis Di to minor axis 2hi and that of outer diameter Do to inner diameter Di, and is applicable to steel elliptical heads with Di/2hi within 1–2.6 and Do/Di within 1.001–1.300.

PTS Benchmark Performed Within IAEA Coordinated Research Project 9

2009 ◽  
Author(s):  
Vladislav Pistora ◽  
Milan Brumovsky
Keyword(s):  
Wall Thickness ◽  
Benchmark Problems ◽  
Thickness Variation ◽  
Large Set ◽  
Research Project ◽  
Integrity Assessment ◽  
Safety Margins ◽  
Sensitivity Studies ◽  
Definition Of ◽  
The Impact

During the period 2005 – 2008, the Coordinated Research Project 9 (CRP 9) “Review and Benchmark of Calculation Methods for Structural Integrity Assessment of RPVs During PTS” was organised by the IAEA. The overall objective of this Coordinated Research Project was to perform benchmark deterministic calculations of a typical pressurised thermal shock (PTS) regime and finally to recommend the best practice for PTS assessment. The benchmark concerns the assessment of the reactor pressure vessel (RPV) resistance against fast fracture for events in the NPP leading to PTS. This assessment is based on the stress intensity factors KI for a postulated crack. The aim of the benchmark was to compare the results obtained by individual participants for well-defined task, to compare the results obtained when applying national codes requirements, and to assess the influence of individual parameters entering the analysis when performing a large set of sensitivity studies. Further aim of this benchmark was to create data which can be used for training of young specialists and for validation of their approach. The benchmark phase of CRP 9 comprised: • Definition of two separate benchmarks for generic WWER-440/213 and PWR-900 (3 Loop) designs, considering the Participants’ own experience and the results of previous international studies. • Basic case analysis of the benchmark problems and application of national code approaches. • Sensitivity studies to assess the impact of individual parameters on the assessment results. The basic (mandatory) case was defined uniquely (all input parameters precisely defined) to enable comparison of the results. Only effect of different models, methods of solving the problems or user effect can be source of the differences in the results, but not the difference in the input data (e.g. material properties, crack geometry, safety margins etc.). The extent and format of output data to be used for comparison were also well-specified. This paper describes the definition of the PTS benchmarks and some examples of the comparative results, like: • variation of temperature through the RPV wall thickness, • variation of stress through the RPV wall thickness, • KI and KIC in dependence on temperature, • variation of KI along crack front, • resulting maximum allowable transition temperature. Finally, it was concluded that the differences among the results were reasonably low and that the methods and models used by the participants can be used for integrity assessment of real RPVs.

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.

Finite Element Analysis of Installation Failures in Engine Cylinder-Liners

2020 ◽  
Author(s):  
Satya Prasad Paruchuru ◽  
Pramila Rani Maturi ◽  
Jashwitha Nuthalapati
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Element Analysis ◽  
Thin Cylinder ◽  
Press Fitting ◽  
Engine Cylinder ◽  
Definition Of ◽  
Cylinder Bore ◽  
Cylinder Liners ◽  
The Impact

Abstract There exist concerns regarding the failures that occur during the installation of thin cylinder-liners of engines at the authorized and unauthorized service centers. Analyzing the probable causes from the points of view of the design, manufacturing, and authorized and unauthorized installation procedures define the problem. The problem involves the simulation of the process of press-fitting the liner into the cylinder bore. A choice of finite element analysis using commercially available software ANSYS helped the analysis of the probable causes of failure. Estimation of the probable loads experienced by the cylinder-liners during the procedures that exist in the installation-process paved the way to the definition of loads that prevail in the problem of relevance. Prediction of the nature of contacts that prevail in the current problem and the impact of the application of the loads enabled the definition of constraints for the simulation procedures. Reference material properties chosen in the conservative sense modeled the problem realistically. The evolution of the recommendations for the manufacturing and installation of thin cylinder-liners concluded the study.

Weld Residual Stress Activities Within the ATLAS+ Project

2018 ◽  
Author(s):  
Mike C. Smith
Keyword(s):  
Residual Stress ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Integrity Assessment ◽  
Weld Residual Stress ◽  
Stress Profiles ◽  
Assessment Procedures ◽  
Design And Manufacture ◽  
The Impact

Weld residual stresses can have significant effects on the service performance and structural integrity of pressure-retaining components in nuclear power plants. Reliable prediction and measurement of residual stress in plant-representative components can be challenging. The impact of residual stress on structural integrity can also be difficult to predict reliably. This paper describes the residual stress activities taking place within ATLAS+, and covers welded mock-up design and manufacture, residual stress measurements and simulation, the development of residual stress profiles for structural integrity assessment, and their incorporation into assessment procedures.

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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