A Fatigue Failure Mechanism of Welded Piping Joints

2005 ◽  
Author(s):  
Tasnim Hassan ◽  
Xiangyang Lu
Keyword(s):  
Residual Stresses ◽  
Fatigue Failure ◽  
Welded Joints ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Pipe Length ◽  
Welding Sequence ◽  
Weld Toe ◽  
Weld Fatigue

Fatigue failures of small bore piping systems have historically occurred in nuclear power plants, resulting in unanticipated plant downtime and substantial financial loss. If the failures were not caused by defects, the reasons of the initiation of fatigue cracks were not clear in many cases. This paper presented a set of weld fatigue response data which pointed to the strain ratcheting response as a probable reason for weld fatigue failure. A systematic set of low-cycle fatigue tests on butt- and socket welded piping joints in the cantilever set up is conducted. A new observation made in these tests is that the recorded strains near the weld toe ratchet continuously, which results in the initiation of fatigue crack(s). Comparison of these ratcheting responses with those from the cyclic bending of straight pipe and ratcheting experiments at the material level indicates that the residual stresses at welded joints may induce the ratcheting responses. This observation is further supported by the symmetric strain response (no ratcheting) at the mid-pipe length, which is located away from the welded joint. At this location, there are no residual stresses to induce ratcheting. It is observed that the fatigue cracks in all experiments occurred at the weld toe location where the ratcheting strain is the largest. The experimental data indicate that the fatigue life of materials is reduced in the presence of ratcheting. It is also observed that the ratcheting is influenced by the welding sequence. One interesting aspect of the weld fatigue data developed is that the ratcheting at the weld joints occurred under a displacement-controlled loading cycle. This study with its limited time and resource could not explore this issue. A plausible reason could be due to material heterogeneity at the welded joints.

Residual Stress and Strain Responses of Welded Piping Joints Under Low-Cycle Fatigue Loading

2009 ◽  
Author(s):  
Pei-Yuan Cheng ◽  
Tasnim Hassan
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Fatigue Failure ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Stress And Strain ◽  
Weld Toe ◽  
Strain Responses

It is well known that residual stress of welded joints influence their fatigue lives. This influence of residual stress is manifested through strain ratcheting response at the weld toe. Among many other reasons, strain ratcheting at the weld toe is anticipated to be a reason of many premature fatigue failure of welded joints. Hence, accurate simulations of weld toe residual stress and strain responses are essential for fatigue life simulation of welded joints. This paper presents results form an ongoing study on fatigue failure of welded piping joints. A modeling scheme for simulating weld toe residual stress and strain response is developed. Uncoupled, thermo-mechanical, finite element analyses are employed for imitating the welding procedure, and thereby simulating the temperature history during welding and initial residual stresses. Simulated residual stresses are validated by comparing against the measured residual stresses. Finite element simulations indicate that both residual stress and resulting strain responses near the weld toe are the key factors in inducing fatigue cracks at the weld toe. Research needs in revealing the fatigue failure mechanisms at the weld toe are discussed.

Finite Element Analyses of Residual Stresses in Typical Welded Joints Used in Nuclear Power Plants and Comparisons With Experiments

2010 ◽  
Author(s):  
Dean Deng ◽  
Kazuo Ogawa ◽  
Nobuyoshi Yanagida ◽  
Koichi Saito
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Residual Stresses ◽  
Welded Joints ◽  
Nuclear Power ◽  
Power Plants ◽  
Butt Joint ◽  
Welding Residual Stress ◽  
Dissimilar Metal ◽  
Water Reactors

Recent discoveries of stress corrosion cracking (SCC) at nickel-based metals in pressurized water reactors (PWRs) and boiling water reactors (BWRs) have raised concerns about safety and integrity of plant components. It has been recognized that welding residual stress is an important factor causing the issue of SCC in a weldment. In this study, both numerical simulation technology and experimental method were employed to investigate the characteristics of welding residual stress distribution in several typical welded joints, which are used in nuclear power plants. These joints include a thick plate butt-welded Alloy 600 joint, a dissimilar metal J-groove set-in joint and a dissimilar metal girth-butt joint. First of all, numerical simulation technology was used to predict welding residual stresses in these three joints, and the influence of heat source model on welding residual stress was examined. Meanwhile, the influence of other thermal processes such as cladding, buttering and heat treatment on the final residual stresses in the dissimilar metal girth-butt joint was also clarified. Secondly, we also measured the residual stresses in three corresponding mock-ups. Finally, the comparisons of the simulation results and the measured data have shed light on how to effectively simulate welding residual stress in these typical joints.

Apply the Acoustoelastic Method to Determine Residual Stresses in Welded Joints

NDT World ◽  
2020 ◽  
pp. 10-17
Author(s):  
Arkady Kamyshev ◽  
Aleksandr Danilov ◽  
Lev Pasmanik ◽  
Aleksandr Getman ◽  
Dmitry Kuzmin ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Weld Metal ◽  
Base Metal ◽  
Welded Joints ◽  
Nuclear Power ◽  
Power Plants ◽  
Stress Measurement ◽  
Metal Structure ◽  
Mechanical Tests ◽  
Residual Welding

The problem of maximum stresses estimation in the weld metal, where the direct measurements are not possible due to the influence of the metal structure on the measurement error, was solved. The influence of features of welding joints manufacturing technology on the structure of the weld metal was also determined. We use several reference welded joints of pipelines at nuclear power plants in our studies. Instrumental estimation of acoustoelasticity parameters in the weld metal in welded joints and in adjacent areas of the base metal was used together with computational modeling of the residual welding stresses distributions. Results obtained demonstrate that the error of stress measurement in the metal in the joint, which is related to the structure of the weld metal, is comparable to the material yield strength. Due to that a direct measurement of the maximum values of welding stresses is not possible. Comparison of results of acoustoelasticity parameters measurements with results of the metal macrostructure studies and mechanical tests allowed us to determine the relationship between peculiarities of structure of the weld metal sections at vertical joints with their tendency to brittle destruction. We propose and justify the NDT method of residual welding stresses in the weld metal. It is based on the principle of residual stresses balancing and employs the results of stress measurements in the base metal by acoustoelasticity. Applicability of non-destructive testing of acoustoelasticity parameters to identify the areas of welded joints with a higher tendency to brittle fracture is also justified.

Fatigue Life of Welded Joints of High-Strength Structural Steel S960QL

2016 ◽  
Vol 250 ◽  
pp. 169-174 ◽  
Author(s):  
Tomasz Slezak ◽  
Lucjan Sniezek
Keyword(s):  
Fatigue Life ◽  
Structural Steel ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Cracking ◽  
High Strength ◽  
Propagation Rate ◽  
Total Strain Amplitude ◽  
Fatigue Life Analysis

The article presents the results of research on low cycle fatigue strength of welded joints of structural steel S960QL. Two types of butt welds were analysed: I-joints and V-joints. The tests were performed under load controlled using the total strain amplitude εac. Fatigue life analysis was conducted based on the Manson-Coffin-Basquin equation, which made it possible to determine fatigue parameters. High concordance was found of the adopted description model with experimental results. Studies have shown differences in the fatigue life of the various joints analysed, wherein I-joints showed about 20-50% higher fatigue life. Fractographic tests of fatigue fractures in joints revealed the details of fatigue cracking and differences in the propagation rate of fatigue cracks.

Growth rate of fatigue cracks in fields of residual stresses in titanium welded joints with different content of embrittling impurities

1990 ◽  
Vol 22 (11) ◽  
pp. 1562-1569 ◽  
Author(s):  
V. T. Troshchenko ◽  
V. V. Pokrovskii ◽  
V. L. Yarusevich ◽  
V. I. Mikhailov ◽  
V. A. Sher
Keyword(s):  
Growth Rate ◽  
Residual Stresses ◽  
Welded Joints ◽  
Fatigue Cracks ◽  
Different Content

scholarly journals Structural-&-Phase Condition and the Damageability of the Welded Joints of Steam Pipelines at Thermal Power Plants

2021 ◽  
pp. 56-63
Author(s):  
Vitaly Dmitrik ◽  
Igor Kasyanenko ◽  
Alexandr Krakhmalyov
Keyword(s):  
Service Life ◽  
Welded Joints ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Thermal Power ◽  
Economic Effect ◽  
Structural Phase ◽  
Initial Structure ◽  
Thermal Power Plants ◽  
Phase Condition

The authors studied the interrelation between the type of structure and the damage rate of the welded joints of steam pipelines made of the heat-resistant pearlitic steels that were operated for a long time, i.e. more than 270 thousand hours in the conditions of creepage and low-cycle fatigue. The purpose of this research was to establish the interrelation between the structural-&-phase condition of the metal used for welded joints of the elements of steam systems and their damageability rate for the service life of welded joints exceeding 270 thousand hours. During the studies, the methods of optical and electron microscopy were used according to the requirements of the guideline documentation and also the methods that are used for the determination of mechanical properties. The level of their reliability has been substantiated and the residual life has been determined. To impart functional performances to welded joints we used well-known methods that were appropriately emended according to the structural changes of above joints. Such changes condition the conversion of the original structure of welded joints into the ferrite-carbide mixture. The availability of the conversion process of the initial structure on the thermal action zone sections (TAZ) of welded joints has essential distinctions due to a different disposition of metal to its own damageability. On the whole, the welded joints are damaged more intensively in comparison to the basic metal of steam pipelines. The analysis of the structural state of welded joints in the steam pipelines of thermal power plants as for the extension of their service life results in a considerable economic effect. Understanding the fact that the metal deterioration in welded joints adheres mainly to the fragile mechanism we managed to establish the level of their damageability that demands the renewal of damaged welded joints. We believe that the damageability level of welded joints that tots up to 0.25 or 0.35 of the volume of their TAZ section should be considered as critical for the service life exceeding 270 thousand hours. The damaged welded joints should be renewed throughout the time period of 15 to 20 thousand hours as soon as the specified damageability level is attained.

Structure and Mechanical Properties of Welded Joints for Nuclear Power Plants of Type MIR 1200

2017 ◽  
Vol 891 ◽  
pp. 201-205
Author(s):  
Ladislav Kander ◽  
Petr Čížek ◽  
Šárka Hermanová ◽  
Zdeněk Říha
Keyword(s):  
Mechanical Properties ◽  
Welded Joints ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Shear Fracture ◽  
Low Cycle Fatigue ◽  
Water Environment ◽  
Temperature Shift ◽  
Pressure Vessels

The paper deals with research, development and verification of production technology of selected welded joints for pressure vessels of primary circuits of nuclear power plants of type MIR 1200. Effect of various welding technology including simulation heat treatment on mechanical and fracture properties have been studied. Four type of homogenous 10GN2MFA – 10GN2MFA type of welded joints have been prepared for experimental programme. Conventional mechanical properties (tensile and impact test) as well as unconventional mechanical properties (fracture mechanics, low-cycle fatigue and stress corrosion cracking in water environment) have been studied. Effect of elevated working temperature on structure and material properties has been evaluated. Temperature dependencies of shear fracture have been plotted and effect of welding procedure on transition temperature shift has been evaluated. Experimental data have been compared with numerical simulation using FEM.

Fatigue Life Prediction of Ship Welded Materials

2005 ◽  
Vol 297-300 ◽  
pp. 743-749
Author(s):  
Min Koo Han ◽  
Mamidala Ramulu
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Crack Closure ◽  
Fatigue Cracks ◽  
Welding Process ◽  
Weld Toe

Fatigue crack propagation life of weld toe crack through residual stress field was estimated using Elber's crack closure concept. Propagation of weld toe crack is heavily influenced by residual stresses caused by the welding process, so it is essential to take into account the effect of residual stresses on the propagation life of a weld toe crack. Fatigue cracks at transverse and longitudinal weld toe was studied, these two cases represent the typical weld joints in ship structures. Numerical and experimental studies are performed for both cases. Residual stresses near the welding area were estimated through a nonlinear thermo-elasto-plastic finite element method and the residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated using the Newman-Forman-de Koning-Henriksen equation, which is based on the Dugdale strip yield model in estimating the crack closure level, U, at different stress ratios. Calculated crack propagation life coincided well with experimental results.

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