Qualification of the Notch Stress Approach for the Fatigue Assessment of Welded Pressure Equipment and Power Plant Components

2017 ◽  
Author(s):  
Jürgen Rudolph ◽  
Ralf Trieglaff ◽  
René Stößlein ◽  
Fabian Hauser
Keyword(s):  
Test Data ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Hot Spot ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Notch Stress

The fatigue assessment of welded joints in different engineering disciplines is usually based on nominal, structural or notch stresses on one hand (elastic concept using component fatigue curves of load controlled test data) and local strains on the other hand (elasto-plastic concept using material fatigue curves of strain-controlled push-pull test data of un-notched and polished standard specimens). The concepts of the first mentioned group are implemented in widespread standards and recommendations such as [1] to [3]. The fatigue assessment procedure of the European standard for unfired pressure vessels (EN 13445-3, Clause 17 & 18 and related annexes) [4] is currently under revision with one focus on the elaboration of user friendly fatigue assessment options for welded components [5]. The current state of the art focuses on the application of an adapted structural hot spot stress approach to the fatigue assessment of welded pressure equipment [5]. Although this is a significant step forward, the implementation of a notch stress approach can furtherly increase the fatigue assessment options by detailed weld seam analysis. The paper focuses on respective methodological proposals and application examples of typical welded joints. The finite element analysis as part of the procedure has to be harmonized with the requirements of the assessment procedure. Of course, the compatibility of the hot spot stress approach and a notch stress approach has to be guaranteed for individual examples. The direct comparison of the different approaches allows for a qualitative evaluation of methods. The application of an appropriate master fatigue curve FAT100 and the limitations with regard of stress/strain ranges in the low cycle fatigue (LCF) regime as well as the fatigue assessment of welded joints with mild weld toe notches is the subject of special considerations. The latest recommendations of German Welding Society (DVS) [6] constitute a reference for the last two subjects raised.

scholarly journals Use of 3D Scan of Weld Joint in Finite Element Analysis and Stochastic Analysis of Hot-Spot Stresses in Tubular Joint for Fatigue Life Estimation

2019 ◽  
Author(s):  
Mikkel L. Larsen ◽  
Vikas Arora ◽  
Marie Lützen ◽  
Ronnie R. Pedersen ◽  
Eric Putnam
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Welded Joints ◽  
Hot Spot ◽  
Strain Range ◽  
Fe Model ◽  
Design Codes ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Weld Toe

Abstract Several methods for modelling and finite element analysis of tubular welded joints are described in various design codes. These codes provide specific recommendations for modelling of the welded joints, using simple weld geometries. In this paper, experimental hot-spot strain range results from a full-scale automatically welded K-node test are compared to corresponding finite element models. As part of investigating the automatically welded K-joint, 3D scans of the weld surfaces have been made. These scans are included in the FE models to determine the accuracy of the FE models. The results are compared to an FE model with a simple weld geometry based on common offshore design codes and a model without any modelled weld. The results show that the FE model with 3D scanned welds is more accurate than the two simple FE models. As the weld toe location of the 3D scanned weld is difficult to locate precisely in the FE model and as misplacement of strain gauges are possible, stochastic finite element modelling is performed to analyse the resulting probabilistic hot-spot stresses. The results show large standard deviations, showing the necessity to evaluate the hot-spot stress method when using 3D scanned welds.

Integral Mean of Yield Concept Applied to Thermal Hot Spots: Validation of a Level 2 Damage Assessment Method

2018 ◽  
Author(s):  
Henry Kwok ◽  
Simon Yuen ◽  
Jorge Penso
Keyword(s):  
Hot Spots ◽  
Damage Assessment ◽  
Hot Spot ◽  
Load Capacity ◽  
Assessment Method ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Element Analysis ◽  
Level 3 ◽  
Level 2

The overall framework for a Level 2 assessment of local thermal hot spot in pressure vessels was first developed by Seshadri [1]. The assessment procedure invokes the concept of integral mean of yield and the concept on a reference volume to determine the reduction of load capacity caused by hot spot damage. This paper investigates the accuracy of this assessment by comparing the results of the Level 2 assessment with a Level 3 assessment (inelastic finite element analysis). Three examples with varying pressure component and hot spot sizes are considered. The comparison yielded a low variance between the Level 2 and Level 3 assessments with the Level 2 assessment being more conservative.

Fatigue Assessment of Trimaran Structure Based on Simplified Procedure

2012 ◽  
Vol 525-526 ◽  
pp. 333-336
Author(s):  
Hui Long Ren ◽  
Shehzad Khurram ◽  
Chun Bo Zhen ◽  
Khurram Asifa
Keyword(s):  
Fatigue Damage ◽  
High Speed ◽  
Hot Spot ◽  
Mathematical Formulation ◽  
Direct Calculation ◽  
Assessment Procedure ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Strength Assessment ◽  
Simplified Procedure

In recent years, Trimaran platform design has got the attention of naval architects owing to its superior seagoing performance. Trimaran structure experiences severe loads due to its unique configuration and high speed, causing stress concentration, especially in cross deck region and accelerate fatigue damage. This paper presents fatigue strength assessment of Trimaran structure by simplified procedure. A methodology is proposed to evaluate fatigue loads and loading conditions by load combinations of direct calculation procedure of Lloyds Register Rules for Classification of Trimaran (LR Rules). Global FE analysis, in ANSYS, is performed to investigate the stress response. The stress range is computed by hot-spot stress approach, and its long term distribution is specified by Weibull distribution. Fatigue damage of selected critical details is calculated using mathematical formulation of simplified fatigue assessment procedure of Common Structure Rules (CSR).

Fatigue Analysis of a Thin Cover Plate Structure in a Light Craft

2015 ◽  
Author(s):  
Till Köder ◽  
Berend Bohlmann
Keyword(s):  
Hot Spot ◽  
Gas Metal Arc Welding ◽  
Plate Thickness ◽  
Fatigue Analysis ◽  
Fatigue Tests ◽  
Cover Plate ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Notch Stress ◽  
Metal Arc Welding

Experimental fatigue analysis of a fillet-welded cover plate detail (‘floating frame’) of small and light craft was carried out at Kiel University of Applied Sciences. The structural detail is an intersection of longitudinal deck stiffener and transverse web frame with a plate thickness of 3.5mm and a doubling length of 100mm. Manual gas metal arc welding was used for the production of the 46mm long transverse fillet welds. The load-controlled constant amplitude fatigue tests at stress ratio R = 0 were supported by 3D finite-element analysis based on laser scans of the weld seams. Structural hot-spot stress, stress linearisation and Xiao and Yamada’s 1mm geometrical stress approaches were applied to the specimens as well as the notch stress concept with reference radii rref = 0.05mm and 1.00mm.

Fatigue Assessment of Aluminum Ship Details by Hotspot Stress Approach

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Bård Wathne Tveiten ◽  
Stig Berge ◽  
Xiaozhi Wang
Keyword(s):  
Finite Element ◽  
Hot Spot ◽  
Experimental Tests ◽  
Fatigue Tests ◽  
Stress Range ◽  
The Finite Element Method ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Modeling Techniques

This paper presents a robust methodology for fatigue assessment of aluminum ship details using a hot-spot stress range approach. A series of fatigue tests of a typical aluminum ship detail was carried out to obtain a design S–N curve. The test detail was analyzed by the finite element method using several modeling techniques and element types. The results from both experimental tests and finite element analysis are discussed. Recommendations on the procedure of fatigue assessment of aluminum ships including S–N curve to be used are also presented.

Fatigue Strength Evaluation of the Load-Carrying Cruciform Fillet Welded Joints Using Hot-Spot Stress

2006 ◽  
Vol 324-325 ◽  
pp. 1281-1284 ◽  
Author(s):  
Byeong Wook Noh ◽  
Jung I. Song ◽  
Sung In Bae
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Hot Spot ◽  
Plate Thickness ◽  
Structural Stress ◽  
Leg Length ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Load Carrying ◽  
Weld Toe

In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

Criteria for Fatigue Failure of Materials: Application in Fatigue Assessment of Structures

2018 ◽  
Vol 26 ◽  
pp. 1-8
Author(s):  
Sergei Petinov ◽  
Ruslan Guchinsky
Keyword(s):  
Fatigue Failure ◽  
Strain Energy ◽  
Hot Spot ◽  
Inelastic Strain ◽  
Fatigue Properties ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Notch Stress ◽  
Assessment Procedures ◽  
Nominal Stress Approach

Presently in rules for fatigue assessment of structures subjected to intensive alternating service loading the Stress-Life (S-N) criteria are recommended in versions of the Nominal stress approach, Hot-spot stress and Notch-stress approach based on using the stress range a representative of the current damage. The criteria and approaches provide assessment of fatigue properties of structures accompanied with a series of approximations and uncertainties. A physically and mechanically more correct procedures might be provided by the Strain-life and Inelastic strain energy criteria for fatigue failure and approaches, although specific with intrinsic sources of approximations. The nature of approximations in the approaches is briefly commented and feasible means of improvement the fatigue assessment procedures and applications are presented.

scholarly journals NUMERICAL METHODS FOR THE FATIGUE ASSESSMENT OF WELDED JOINTS: INFLUENCE OF MISALIGNMENT AND GEOMETRIC WELD IMPERFECTIONS

2017 ◽  
Vol 9 (1) ◽  
pp. 9-24 ◽  
Author(s):  
Andreas TARAS ◽  
Harald UNTERWEGER
Keyword(s):  
Numerical Methods ◽  
Welded Joints ◽  
Numerical Models ◽  
Hot Spot ◽  
Nominal Stress ◽  
Geometric Imperfections ◽  
Hot Spot Stress ◽  
Notch Stress ◽  
Effective Notch Stress ◽  
Nominal Stress Approach

The fatigue design life of welded joints in steel structures is increasingly assessed by using numerical models and methods, such as the structural (hot-spot) stress method and the effective notch stress method. When compared to the classical design approach using nominal stress S-N design curves, these methods offer the advantage of flexibility and a wider scope of application. However, a number of questions arise when these methods are used to assess geometrically "imperfect" welded joints, such as joints with plate misalignments or excessive weld convexity or concavity. In these cases, the classical S-N curves are known to cover imperfections up to the common tolerance classes for fatigue-prone welded joints (e.g. in accordance with ISO 5817 class B). For the numerical methods, differing and conflicting recommendations exist on how to account for the geometric imperfections in the welded joints, with little or no background to these recommendations available. In this paper, a study is presented in which two standard welded joints (butt welds between plates of equal and unequal thickness; T-joints with fillet welds) are analysed with the help of the structural (hot-spot) stress and the effective notch stress approach, considering various levels of geometric imperfection up to the tolerance limits, and the resulting fatigue life predictions are compared to test results from the literature and the nominal stress approach predictions. Since the nominal stress approach curves are based on reliable statistical data and desired survival probabilities for these known, standard cases, this methodology allows one to determine the correct application of the numerical methods to cases with geometric imperfections. This information may be used for a pertinent refinement of design recommendations for these methods, as well as for cases where these methods are applied to fitness-for-purpose assessments - e.g. because the nominal stress approach is not applicable.

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