Fatigue Life of Welded Joints of AISI 347 Stainless Steel Under Thermomechanical and Variable Amplitude Loading

2018 ◽  
Author(s):  
Alexander Bosch ◽  
Sophie Schackert ◽  
Michael Vormwald ◽  
Christoph Schweizer
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Power Plants ◽  
Crack Opening ◽  
Base Material ◽  
Damage Parameter ◽  
The One ◽  
Development And Validation ◽  
Flexible Operation

The change in operation of conventional power plants — due to the increasing use of renewable energies — from a stationary to a more flexible operation, causes additional stresses to the components by a high amount of smaller load cycles. This fact results in a demand for validated new concepts to estimate fatigue life especially for welded joints which are the weak parts within the piping. Resulting from the measured stains during operation in the LCF regime, a non-linear fracture mechanics based concept was chosen. For the development and validation of the model, different experiment types are carried out using various types of specimens. To consider the influence of different microstructures within a welded component, specimens made of X6CrNiNb18-10 (AISI 347) with the microstructure found in the base material on the one side, and as found in the HAZ on the other side are used. To take the influence of a mechanical and microstructural notch into account, notched specimens of X6CrNiNb18-10 (AISI 347), and welded specimens made of X6CrNiNb18-10 (AISI 347, base material) and X5CrNiNb19-9 (weld material) are used. Experiments are performed with all types of specimens with an increasing complexity from constant amplitude loading to operational loading. The developed nonlinear fracture mechanics based lifetime model uses the effective cyclic J-Integral normalized to the crack length to replace crack growth calculation by a linear damage accumulation. To consider the loading history an algorithm for the calculation of crack opening and crack closure is used. The advantages of this approach are shown by a comparison with damage calculations based on the damage parameter by Smith, Watson and Topper and based solely on the strain ranges. The differences in the concepts will be highlighted and used for further considerations of how to advance the lifetime prediction model for variable amplitudes. The presented work gives an overview of the preliminary results of the current work on the AiF research project 18842 N ‘Extended damage concepts for thermomechanical loading under variable amplitudes and plastic deformation’.

Grades 92 and 23: Weldability Assessment and Long-Term Performances for Power Generation Applications

2008 ◽  
Vol 580-582 ◽  
pp. 383-388
Author(s):  
Emmanuel Bauné ◽  
E. Galand ◽  
B. Leduey ◽  
G. Liberati ◽  
G. Cumino ◽  
...  
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Power Plants ◽  
Product Family ◽  
Base Material ◽  
Advanced Materials ◽  
Creep Properties ◽  
Steam Parameters ◽  
Term Creep

Increased efficiency and emission reduction in modern power plants lead to the use of new advanced materials with enhanced creep strength, with the objective to increase the steam parameters of power plants. With over ten years on market and wide experience related to its use, ASTM Grade 92 is becoming one of the most required materials when high service temperatures are reached (max. 610°C). Its composition, with 9%Cr and 1.5%W, gives rise to martensitic microstructures which offer very high creep strength and long term stability. The improved weldability and creep-strength between 500 and 580°C of the low alloy ASTM Grade 23, as well as a cost advantage over higher Cr materials in this temperature range, make it one of the possible candidates to meet the stringent requirements of modern power plants. Air Liquide Welding (ALW) has optimized and distributes a complete product family for the welding of Grades 23 and 92. TenarisDalmine (TD) focused on the development of Grade 23 tubes and pipes and is working on the development of Grade 92. A deep characterization work of the microstructural evolution and long term creep performances of these high temperature resistant materials was thus undertaken by ALW and TD, in collaboration with the Centro Sviluppo Materiali (CSM). The joint characterization program consisted in the assessment of welded joints creep properties. Welded joints were produced using the gas tungsten (GTAW), shielded metal (SMAW) and submerged arc welding (SAW) processes. Mechanical and creep properties of weldments were measured both in the as welded and post weld heat treated conditions and proper WPS’s were designed in a manner such that industrial production needs were satisfied. Short term creep resistance of cross weld specimens was measured to be within the base material acceptance criteria. Long term base material and cross weld creep performance evaluation are now in progress.

scholarly journals An overview of application of micromechanical models in ductile fracture analysis of welded joints

2020 ◽  
Vol 47 (1) ◽  
pp. 33-62
Author(s):  
M. Rakin ◽  
B. Medjo ◽  
N. Gubeljak ◽  
A. Sedmak
Keyword(s):  
Ductile Fracture ◽  
Welded Joints ◽  
Void Nucleation ◽  
Base Material ◽  
Damage Parameter ◽  
Damage Development ◽  
Long Time ◽  
Actual Material ◽  
Micromechanical Models

Fracture of welded joints has been an important research and industrial topic for a long time, having in mind the key role of welded joints in ensuring the safe operation and integrity of welded structures. This work contains an overview of application of micromechanical models to ductile fracture of welded joints. The main benefit of these models, in comparison with the classical fracture mechanics approach, is consideration of the local quantities (stress and strain) in prediction of damage development. The damage is quantified through the value of the damage parameter, which is typically related to the void nucleation, growth and coalescence for ductile fracture of metallic materials, i.e. the description of the material can be related to the actual material behaviour during fracture. Most of the presented studies, including those published by the present authors, are performed on steel as the base material, and the rest deal with aluminium alloys.

Fatigue life assessment of welded structures based on fracture mechanics

2015 ◽  
Vol 6 (1) ◽  
pp. 2-25
Author(s):  
A. Krasovskyy ◽  
A. Virta
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Welding Process ◽  
Life Assessment ◽  
Lifetime Estimation ◽  
Worst Case ◽  
Welded Structures ◽  
Content Type ◽  
Fatigue Life Assessment

Purpose – Even though modern welding technology has improved, initial defects on weld notches cannot be avoided. Assuming the existence of crack-like flaws after the welding process, the stage of a fatigue crack nucleation becomes insignificant and the threshold for the initial crack propagation can be used as a criterion for very high cycle fatigue whereas crack growth analysis can be applied for the lifetime estimation at lower number of cycles. The purpose of this paper is to present a mechanism based approach for lifetime estimation of welded joints, subjected to a multiaxial non-proportional loading. Design/methodology/approach – The proposed method, which is based on the welding process simulation, thermophysical material modeling and fracture mechanics, considers the most important aspects for fatigue of welds. Applying worst-case assumptions, fatigue limits derived by the weight function method can be then used for the fatigue assessment of complex welded structures. Findings – An accurate mechanism based method for the fatigue life assessment of welded joints has been presented and validated. Originality/value – Compared to the fatigue limits provided by design codes, the proposed method offers more accurate lifetime estimation, a better understanding of interactions between welding process and fatigue behavior. It gives more possibilities to optimize the welding process specifically for the considered material, weld type and loading in order to achieve the full cost and weight optimization potential for industrial applications.

scholarly journals Behaviour of Ni-Based Alloys for Fossil-Fired Power Plant Components in the Long-Term Creep Regime

2011 ◽  
Vol 278 ◽  
pp. 241-246 ◽  
Author(s):  
Magdalena Speicher ◽  
Andreas Klenk ◽  
Karl Maile ◽  
Eberhard Roos
Keyword(s):  
Power Plant ◽  
Welded Joints ◽  
Power Plants ◽  
High Efficiency ◽  
Base Material ◽  
Creep Rupture ◽  
Materials Testing ◽  
Steam Parameters ◽  
Term Creep ◽  
Plant Components

High efficiency steam power plants are planned to operate at temperatures higher than 700°C and at a pressure of up to 350 bar. Due to this increase of the steam parameters, Ni-based alloys are required for constructing these plants. Materials testing - based on appropriate manufacturing and design criteria - is necessary in order to have a reliable data base of the relevant design characteristics. Additionally, a better understanding of the specific material behaviour under service like loading conditions for the evaluation of possible damage mechanisms is essential. This paper describes research on the behaviour of thick-walled power plant components made of Alloy 617 mod. and Alloy 263. Results from basic qualification programs with standard specimens including welded joints show the applicability of the materials. Results from creep rupture tests of base material and welded joints and microstructural investigations to obtain information on precipitations and dislocations in the virgin and aged conditions are presented. Information on the influence of chemical composition on creep rupture was obtained by analysing creep rupture data sets.

Fatigue Crack Growth Assessment of Welded Joints in Ships Structures: A Reliability-Based Sensitivity Study

2006 ◽  
Author(s):  
Cesare Mario Rizzo ◽  
Efren Ayala-Uraga
Keyword(s):  
Sensitivity Analysis ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Sensitivity Study ◽  
Reliability Model ◽  
Structural Details ◽  
Before And After ◽  
Influencing Parameters ◽  
Growth Assessment

Fatigue life calculations have been recently introduced as explicit checks in classification societies rules for shipbuilding. Such checks are based on the classic S-N approach, which cannot be easily applied to the condition assessment of structural details. Fracture mechanics approach allows describing the structural degradation of ageing structures and the reliability framework accounts for the inherent probabilistic aspects of fatigue. This approach gains relevance as many ship tankers are being converted to operate as offshore ships. This paper carries out a sensitivity analysis of the reliability model for fatigue life calculations of typical ship’s welded joints based on fracture mechanics, aiming to select the most influencing parameters, before and after inspection updating.

Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method

2010 ◽  
Vol 19 (9) ◽  
pp. 1225-1234 ◽  
Author(s):  
A. M. Al-Mukhtar ◽  
H. Biermann ◽  
P. Hübner ◽  
S. Henkel
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints

scholarly journals Notch effect of welded joint

2018 ◽  
Vol 165 ◽  
pp. 21003 ◽  
Author(s):  
Vladimír Chmelko ◽  
Matúš Margetin ◽  
Michal Harakal’
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Weld Joint ◽  
Welded Joints ◽  
Structural Changes ◽  
Welded Joint ◽  
Base Material ◽  
Notch Effect ◽  
Internal Defects ◽  
Technological Factors

In general, the welded joints are multifactorial notches. This study is focused to separate the geometrical influence (when the weld can be seen on the surface) and technological factors (internal defects of the weld, structural changes of the material and residual stress) on its fatigue life. Proposed methodology of this separation comes out from the cyclic test of three specimens – group with existing weld, group without weld joint (base material) and another group where was removed outer geometry of the weld.

Sign in / Sign up

Export Citation Format

Share Document