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Meeting 2020 AWS Professional Program
Symposium 2020 AWS Professional Program
Presentation Title Low-cycle Fatigue Evaluations of Ni-Steel Dissimilar Joints for Coke Drum Welding Repairs
Author(s) Shutong Zhang, Sebastian Romo, Rafael Arthur Giorjao, Jorge Penso, Haixia Guo, Simon Yuen, Lisa Ely, Antonio Ramirez
On-Site Speaker (Planned) Shutong Zhang
Abstract Scope Introduction Coke drums are large pressure vessels used in oil refineries to transform heavy residual oil to light-weight oil molecules and solid cokes through the delayed coking process. Each delayed coking unit consists of at least two coke drums, which work alternatively to allow the continuous injections of residual oil. During the operation cycles, coke drums endure severe thermal and mechanical loadings, which lead to coke drum damage such as bulging and cracking. Low-cycle fatigue has been widely regarded as the major cause that leads to the damage, because the stresses within the coke drum material can exceed the yield stress and induce plastic deformations. Welding repairs using temper bead welding (TBW) techniques are widely adopted to replace the cracked regions and restore the local mechanical properties. The nickel-base alloys including Alloy 625 and Alloy 182 have been used as the filler materials because of their matching thermal expansion coefficient and good chemical compatibility with the low alloy steel base metal (BM) and the 410s stainless steel clad. However, they tend to exhibit significant cyclic hardening beyond the base metal and induce stress concentrations in the joint region due to the strength mismatches. In addition, metallurgical reasons such as welding defects and dilutions can reduce the weld metal resistance against fatigue failures. In this study, two Ni-steel dissimilar joints are evaluated based on the low-cycle fatigue tests and metallurgical characterizations. The goal of this work is to measure the low-cycle fatigue behaviors of the two joints and investigate the crack-susceptible regions through failure analysis. Experimental Methods Two welding mockups were fabricated using the shield metal arc welding (SMAW) process with the TBW techniques. The weld metals are Alloy 625 (ENiCrMo-3) and Alloy 182 (ENiCrFe-3) and the base metal is 1.25Cr-0.5Mo steel with a 410s clad layer. Two types of dog-bone specimens were extracted from the welding mockups transverse to the welding directions. The weld metal (WM) specimens contain a full weld metal region within the gage length, while the transition zone (TZ) specimens include the transition interface at the center of the gage length. WM and TZ specimens of the two different weld metals were evaluated using the Gleeble-based isothermal low-cycle fatigue (ILCF) tests. The tests are performed at a fully-reversed (R=-1) strain-control condition at three different strain amplitudes (1.0%, 1.5% and 2.0%) and the temperature is held isothermally at 250C (482F). On the other hand, the microstructures of the two welding mockups were characterized using optical microscope (OM) and scanning electron microscope (SEM). The TZ samples were extracted to contain the regions of WM, BM and HAZ and the samples were etched using 2.0% Nital and 10% Chromic Acid electrolytically to reveal ferritic and nickel microstructures respectively. In addition, fracture surfaces of the failed dog-bone specimens were analyzed with an Olympus-DSX510 depth of field microscope for the surface morphologies. Electron backscatter diffraction (EBSD) images of weld metal and transition zone specimens were taken before and after tests to reveal the strain distributions and crystal misorientations of the plastically deformed regions. Results and Discussion The cyclic stress responses of the weld metals show that both nickel-base alloys, Alloy 182 and Alloy 625, exhibit cyclic hardening at the initial cycles, followed by a saturation stage before the failures occur. However, Alloy 625 WM showed much higher peak stresses than Alloy 182 WM, overmatching the 1.25Cr-0.5Mo BM; Alloy 182 WM slightly under-matched the BM at the first cycle but quickly over-matched it due to the cyclic hardening. The experimentally obtained cyclic strain curves showed that both nickel WMs have similar fatigue life but inferior to that of the BM. On the other hand, the cyclic hardening observed in the Alloy 182 TZ specimens was in contrast to the flattened cyclic responses of Alloy 625 TZ specimens. In addition, the fatigue life of Alloy 182 TZ was much shorter than that of Alloy 625 TZ. The reason for the results can be rationalized by the unbalanced plasticity within the TZs. For Alloy 625 TZ specimens, most of the plastic deformations occurred in the BM due to the overmatching WM strength. For Alloy 182 TZ specimens, most of the plastic deformation occurred in the WM. This could be supported by the failure analysis, as the macrocrack occurred in the BM region of Alloy 625 TZ while it occurred along the fusion boundary in the Alloy 182 WM. Metallurgical analysis showed that particles such as Nb carbides and Ti oxide inclusions were dispersed along the interdendritic regions and solidification grain boundaries. The inclusion particles were observed at dimples of the fracture surfaces along with the fatigue striations marks. In addition, EBSD strain analysis of the Alloy 182 TZ zone showed the transgranular crack propagations with fine-grain structures on both sides of the crack. Conclusions Two Nickel WMs and their TZs were evaluated based on the low-cycle fatigue tests and metallurgical characterizations. Both WMs showed similar cyclic behaviors and fatigue life, but Alloy 625 WMs exhibited much higher strength over Alloy 182 WMs and the 1.25Cr-0.5Mo BM at the same strain amplitudes. Due to the strength mismatches, the low-strength regions became the crack susceptible areas. This led to the differences of failure locations and fatigue behaviors between the TZ zones of the two Nickel welds. Failure analysis was performed by fracture surface characterizations and EBSD strain analysis. The results showed that the cracks propagated transgranularly in the Alloy 182 WM and caused the formation of fine grains along the crack path.
Proceedings Inclusion? Definite: Other (describe below)


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Analysis of Dynamic Evolution of Weld Pool for the Real-Time Monitoring of Penetration Using Deep Learning
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Characterization of the Fourth Generation of Nickel-Chromium Welding Products for Nuclear Service
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Computational Modeling on Defect Formation during Self-Reacting Friction Stir Welding
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Correlating Laser Power and Microstructural Properties of Additively Manufactured Ti-6Al-4V Fabricated by Directed Energy Deposition
Creep Strength Variation in Simulated ICHAZs of Grade 91 Steel
Design of an Austenitic Steel Weldment System Using ICME
Development of Industry 4.0 Software for Arc-Welding Energy Monitoring and Traceability
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Development, Optimization, and Mechanical Testing of ER80S-G Girth Welds on Internally Clad API 5L Grade X65 Pipes
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Effect of Chemical Composition of Welding Consumable on Slag Formation and Weld Corrosion Resistance
Effect of Heating Rate on Austenite Formation in a Low Carbon Microalloyed Steel
Effect of Phase Transformations on Mechanical Properties of Ti Free Grade 300 Maraging Steel Manufactured by Laser Powder Bed Fusion (LPBF)
Electron Beam Brazing of Stainless Steel using NIORO Filler Metal
Evaluation of Braze Joints for Hydrogen Purification Diffuser
Experimental Studies of Wire Feeding Electron Beam Welding-Brazing of Aluminum to Stainless Steel and Titanium
Failure Analysis: Evaluating a Low Strength Solder Joint
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In-situ Measurement and Numerical Simulation for Linear Friction Welding of Complex Titanium Structures
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Induction Heating-Assisted Friction Stir Welding in Low Carbon Steel Plates
Influence of Composition on the Solidification and Mechanical Properties of HP-Modified Heat-Resistant Austenitic Stainless Steels
Influence of Cooling Rate on Microstructure Formation in Rapid Solidification of Ni2MnGa Alloy
Influence of Hydrogen on the Softened HAZ in Various Carbon Steel Welds
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Integrated Modeling of Multi-Process Automotive Lap Joining – Part 3: Microstructure and Mechanical Properties
Investigation of a Curly Toolpath in Friction Stir Welding
Investigation of Laves Phase Formation in Inconel 718 Fabricated by Laser Powder Bed Fusion
Investigation of Thermally Assisted Friction Element Welding
Joining Dissimilar Metals of DP590 Steel and AZ31B Magnesium Sheets by Ultrasonic Spot Welding
Low-cycle Fatigue Evaluations of Ni-Steel Dissimilar Joints for Coke Drum Welding Repairs
Machine Learning for Automatic Recognition of Microstructures
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Mechanical Properties Assessment of Carbon and Low-Alloy Steel Parts Built by GMA-DED
Mechanics of the Solid-State Bonding and Prediction of Thermomechanical Responses in Friction Stir Welding
Mechanistic Models and Machine Learning to Mitigate Common Defects in Metal Printing
Metallic Powder Core Tubular Wire Development for Additive Manufacturing
Microstructural and Mechanical Property Characterization of Reaction Synthesis Aluminum Metal Matrix Composites Produced by Additive Manufacturing
Microstructural Characterization and Mechanical Property Evaluation of Fusion Zones in a 10 wt% Ni Steel Weld Metal
Microstructure and Mechanical Properties of 410 Stainless Steel Using Different Shielding Gases in the Wire-Arc Additive Process
Microstructure and Mechanical Properties of Intercritical-Treated Grade 91 Steel
Microstructures and Microhardness of LENS DED Deposits of Ti/TiC MMCs
Mitigation of Liquid Metal Embrittlement in Galvannealed AHSS Welds Using High Entropy Alloy Filler
Modal Analysis of Ultrasonic Welding to Enable Multi-Spot Dissimilar Material Joining
Modeling and Comparing Human Welder’s Operation Between Stereo Camera and Virtual Reality
Modeling of In-Situ Tempering of a Creep Resistant Ferritic Martensitic Steel during Multi-Layer Additive Manufacturing
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Modelling of Laser Cladding Using Gaussian Heat Source Profile and Verification with Experimental Results
Multi-Scale and Multi-Physics Modeling of Process-Microstructure-Property Relationship in Metal Additive Manufacturing
New Approaches in Friction Welding Advanced PM Nickel Base Superalloys
Numerical Study on Heat Transfer Mechanisms in Electric Arc Columns
Optimization of Tool Path and Microstructure in Large Scale Metal Additive Manufacturing with Multi-Heat Sources
Phase Transformation Analysis and Microstructural Characterization of the Heat Affected Zone in Grade 92 Steel Welds
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Process Control Using Predictive Equations for Zero Programming Laser Cladding Facility
Process, Microstructure and Fracture Mode of Magnesium to Steel Dissimilar Metal Spot Joints
Pulsed-Arc Welding of Battery Tabs for Vehicle Electrification
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Recent Developments in Metal Additive Manufacturing
Research and Development of a Novel TIG Welding Technology for Joining Thin Sheets Applying in Metal Forming Field
Residual Stress Measurement on High-Strength Steel Panels for Shipbuilding Application
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Weld Metal Cooling Rate-Mechanical Property Response of Fe-10Ni Steel Gas Metal Arc Weld Deposits and Other Experimental Observations
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Welding of FeMnAl High-Manganese Lightweight Steel
Wetting and Low Temperature Bonding of Zirconia Metallized with Ti-Containing Active Solders

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