Study on Skirt-to-Shell Attachment of Coke Drum by Evaluation of Fatigue Strength of Weld Metal

2011 ◽  
Author(s):  
Yasuhiko Sasaki ◽  
Shinta Niimoto
Keyword(s):  
Fatigue Strength ◽  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Fatigue Design ◽  
Inner Radius ◽  
Section Viii

A skirt-to-shell attachment of a coke drum experience severe thermal cyclic stresses, which cause failures due to low cycle fatigue. Various skirt attachment designs, therefore, have been proposed and implemented. A design where the skirt is attached by a weld build-up is most commonly used. A design where the skirt is attached to the drum shell by utilizing an integral machined plate or forging has been utilized in several projects. One of the advantages of the integral skirt attachment is that a large inner radius can be formed which allows reducing stress concentration compared with the weld build-up design. This advantage can be confirmed easily by FE-analysis in recent years [1] [2] [3]. Another major advantage of the integral skirt attachment is that the area of highest stress intensity is located at the base metal section, not at the weld metal or the heat affected zone which are generally thought to have lower fatigue strength. The fatigue design curve from ASME Section VIII Division 2 [9] is based on fatigue tests for the base metal. It is necessary to reveal differences of fatigue strength among these metals. This paper describes a comparison of fatigue strength of three metals: i) base metal ii) weld metal iii) heat affected zone provided by the low cycle fatigue test for 1 1/4Cr-1/2Mo materials. Our results indicate that the fatigue life of the base metal is about twice as long as that of the weld metal and about three times as long as the heat affected zone. Accordingly, the integral skirt attachment is more resistant to cracking than its welded counterpart from a fatigue strength viewpoint.

High Temperature, Low Cycle Fatigue Characterization of P91 Weld and Heat Affected Zone Material

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
T. P. Farragher ◽  
S. Scully ◽  
N. P. O'Dowd ◽  
C. J. Hyde ◽  
S. B. Leen
Keyword(s):  
High Temperature ◽  
Weld Metal ◽  
Heat Affected Zone ◽  
Low Cycle Fatigue ◽  
Base Material ◽  
Strain Response ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Weld Material ◽  
The Cross

The high temperature low cycle fatigue behavior of P91 weld metal (WM) and weld joints (cross-weld) is presented. Strain-controlled tests have been carried out at 400 °C and 500 °C. The cyclic behavior of the weld material (WM) and cross-weld (CW) specimens are compared with previously published base material (BM) tests. The weld material is shown to give a significantly harder and stiffer stress–strain response than both the base material and the cross-weld material. The cross-weld tests exhibited a cyclic stress–strain response, which was similar to that of the base material. All specimen types exhibited cyclic softening but the degree of softening exhibited by the cross-weld specimens was lower than that of the base material and all-weld tests. Finite element models of the base metal, weld metal and cross-weld test specimens are developed and employed for identification of the cyclic viscoplasticity material parameters. Heat affected zone (HAZ) cracking was observed for the cross-weld tests.

Evaluation of Low-Cycle Fatigue in Simulated PWR Environment

2006 ◽  
Vol 326-328 ◽  
pp. 1011-1014 ◽  
Author(s):  
Ill Seok Jeong ◽  
Sang Jai Kim ◽  
Taek Ho Song ◽  
Sung Yull Hong
Keyword(s):  
Fatigue Life ◽  
Nuclear Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Water Environment ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Fatigue Design ◽  
Number Of Cycles ◽  
Measured Length

For developing fatigue design curve of cast stainless steel that is used in piping material of nuclear power plants, a low-cycle fatigue test rig was built. It is capable of performing tests in pressurized high temperature water environment of PWR. Cylindrical solid fatigue specimens of CF8M were used for the strain-controlled environmental fatigue tests. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitude at 0.04%/s strain rates. The disparity between target length and measured length of specimens was corrected by using finite element method. The corrected test results showed similar fatigue life trend with other previous results.

Isothermal Low-Cycle Fatigue Evaluation of External Weld Repair Using Alloy 182 Filler Metal With Backing Plate Design

2020 ◽  
Author(s):  
Shutong Zhang ◽  
Sebastian A. Romo ◽  
Jorge Penso ◽  
Haixia Guo ◽  
Lisa Ely ◽  
...  
Keyword(s):  
Weld Metal ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Pressure Vessels ◽  
Cycle Fatigue ◽  
Residual Oil ◽  
Weld Repair ◽  
Oil Refineries ◽  
Backing Plate ◽  
Dog Bone

Abstract Coke drums are pressure vessels used in the delayed coking process at oil refineries, which transform heavy residual oil into light-weight hydrocarbon molecules and solid coke through thermal cracking. Due to the severe thermal and mechanical loadings during operation, these vessels experienced low-cycle fatigue failure, which led to shell and skirt damage such as bulging and cracking. External weld repairs using the temper bead technique have been widely applied to repair damaged regions caused by bulging and cracking for preventing the leaks of the residual oil contents. However, a substantial proportion of the external repairs have been reported to experience post-repair cracking issues. In this study, an external weld repair mockup with a backing plate was evaluated through metallurgical characterizations and isothermal low-cycle fatigue tests. The micro-hardness mapping identified the mismatching interfaces from base metal to weld metal (WM) and from root passes to internal clad. Four types of dog-bone samples were extracted from the weld: weld metal, heat affected zone, internal clad and backing plate. These samples were used to evaluate the fatigue resistance of weld metal and transition zone under low-cycle fatigue tests. Failure analysis showed that weld metal samples were susceptible to multiple-crack initiations, while other transition samples failed at mismatching interfaces or stress concentration points at weld toes.

The Thermo-Mechanical Behaviour of Alloy 600 and Alloy 82 Materials

2018 ◽  
Author(s):  
Vasileios Akrivos ◽  
Mike C. Smith
Keyword(s):  
Weld Metal ◽  
Low Cycle Fatigue ◽  
Mechanical Tests ◽  
Fatigue Tests ◽  
Parent Material ◽  
Model Parameters ◽  
Alloy 600 ◽  
Cycle Fatigue ◽  
Chaboche Model ◽  
Different Temperatures

Isothermal uniaxial low cycle fatigue tests have been performed at two different total strain ranges (1.5% and 2.5%) and at different temperatures (20, 200, 400 and 600°C) for Alloy 600 and Inconel 82 materials. The materials hardening behaviour has been fitted using the Lemaitre Chaboche formulations using different fitting strategies. Thermo mechanical tests have been performed using a Gleeble machine on both parent material and weld metal. In these tests thermal cycles were applied to a constrained specimen simulating the welding conditions in both the heat affected zone and a weld bead when subsequent beads are deposited alongside. The tests were modelled using two different FE codes, namely Code_Aster and Abaqus. This allowed the validation of the Lemaitre-Chaboche model parameters when the material is subjected to realistic thermo-mechanical cycles. Simulations were conducted using both annealing and/or viscous recovery features to examine their impact on the predicted response.

Comparison of Ni-Steel Dissimilar Joints for Coke Drum External Weld Repairs Based on Isothermal Low-Cycle Fatigue Tests

2021 ◽  
Author(s):  
Shutong Zhang ◽  
Sebastian Romo ◽  
Rafael Arthur Giorjao ◽  
Jorge Penso ◽  
Haixia Guo ◽  
...  
Keyword(s):  
Experimental Data ◽  
Base Metal ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Alloy 625 ◽  
Weld Joints ◽  
Nickel Base ◽  
Filler Metals

Abstract Low-cycle fatigue failure has been widely accepted as the key mechanism causing damages of coke drums during cyclic thermal-mechanical loadings. Common damages of coke drums known as bulging and cracking are associated with accumulative plasticity caused by thermal and mechanical strains. External repairs using temper-bead welding techniques are implemented to repair welds in the damaged areas of coke drums, which provide structural support to the vessels. Compared with matching filler metals, Ni-base fillers including alloy 625 and alloy 182 are compatible with both low-alloy steel base metal and internal clads in terms of weldability and thermal expansion. However, the differences of yield strengths and cyclic hardening behaviors of nickel-base alloys from base metals compromise the fatigue resistances of weld joints. In this study, alloy 182 and alloy 625 repair coupons were evaluated and compared based on isothermal low-cycle fatigue tests. Low-cycle fatigue behaviors of both weld metals and 1.25Cr-0.5Mo base metal were measured at 1.0%, 1.5% and 2.0% strain amplitudes. Test results indicate both nickel-base filler metals exhibit overmatching strength over the base metal due to cyclic hardening. Low-cycle fatigue tests of Heat Affected zone (HAZ) samples show the failures of alloy 625 weld joints occur in the base metal, while the failures of alloy 182 weld joints occur along the fusion boundary. The observations show strength mismatch and fatigue resistance are the key factors to determine failure locations of the joints. In addition, cyclic hardening coefficients based on kinematic hardening model were extracted from experimental data to simulate the cyclic behaviors of the weld joints. Finite element simulation results were shown to be consistent with experimental data at stabilized cycles. Cyclic behaviors of weld metal and base metal within a weld transition sample were calculated based on the numerical model.

High Temperature Low-Cycle Fatigue of Friction Welded Joints-Type 304-304 Stainless Steel and Alloy 718-718 Nickel Base Superalloy

1993 ◽  
Vol 115 (1) ◽  
pp. 109-115
Author(s):  
T. Wakai ◽  
M. Sakane ◽  
M. Ohnami ◽  
K. Okita ◽  
Y. Fukuchi
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Fatigue Strength ◽  
Base Metal ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
304 Stainless Steel ◽  
Alloy 718 ◽  
Cycle Fatigue ◽  
Type 304

This paper assesses the high-temperature low-cycle fatigue of the Type 304 stainless steel and Alloy 718 superalloy friction-welded joints. Strain controlled low-cycle fatigue tests for 304-304 and 718-718 friction-welded specimens were carried out at 923K in air to obtain the fatigue strength of the joints. These materials were selected as the cyclic hardening and softening materials, respectively. The 304-304 welded specimens showed inferior fatigue strength in comparison with the base metal while the 718-718 specimens exhibited fatigue strength equivalent to that of the base metal. The difference in the fatigue strength between the two materials is discussed from the viewpoint of the cyclic deformation behavior and strain reduction at weld interface.

scholarly journals Prediction of the Ultra-Low-Cycle Fatigue Damage of Q345qC Steel and its Weld Joint

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4014 ◽  
Author(s):  
Qin Tian ◽  
Hanqing Zhuge ◽  
Xu Xie
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Plastic Strain ◽  
Weld Metal ◽  
Base Metal ◽  
Weld Joint ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Experimental Values ◽  
Strain Threshold

Based on the continuum damage mechanics model (CDM) for monotonic tension, a new CDM for ultra-low-cycle fatigue (ULCF) is put forward to predict ULCF damage of steel and its weld joint under strong earthquakes. The base metal, heat-affected zone and weld metal of Q345qC steel were considered as research objects, and the uniaxial plastic strain threshold of the CDM model was calibrated via tensile testing combined with finite element analysis of notched round bar specimens. ULCF tests of the base metal and weld specimens were carried out to analyse their fatigue life, fracture life and post-fracture path. Based on the calibrated uniaxial plastic strain threshold, the finite element models of base metal and weld specimens suitable for CDM model were established by ABAQUS. The calibration results of material parameters show that the weld metal has the lowest plastic strain threshold and the largest dispersion coefficient at the plastic strain threshold. Prediction results under cyclic loading with a large strain were compared with experimental values, and results showed that the predicted crack initiation and fracture lives of the base metal and weld specimens are lower than their corresponding experimental values. The predicted errors of crack initiation life and fracture life decrease with increasing strain level. The development law of the damage variable reveals exponential growth combined with a stepped pattern. The CDM model can also accurately predict the number of cycles to initial damage. Taking the results together, the CDM of the ULCF of the base metal and weld specimens could successfully predict post-fracture paths.

Fatigue resistance of Fe3Al-based alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
Florian Gang ◽  
Manja Krüger ◽  
Alexandra Laskowsky ◽  
Heike Rühe ◽  
Joachim H. Schneibel ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Iron Aluminide ◽  
Cycle Fatigue ◽  
Grain Sizes ◽  
Cast Alloys

ABSTRACTThe low cycle fatigue (LCF) behaviour of two cast as well as two hot extruded Fe3Al-based iron aluminide alloys, either with or without Cr, is investigated. All four alloys contain microalloying additions of Zr, Nb, C and B. Fatigue tests were carried out under strain control for strain amplitudes in the range of εa = 0.1 – 0.4 % for the cast alloys and εa = 0.1 – 0.7 % for the extruded materials, at frequencies of 1 Hz (extruded Fe3Al) and 3 Hz (all other alloys) and at room temperature and 300 °C. Within the first cycles all alloys show strong cyclic hardening. Furthermore the fatigue strain – fatigue life curves are steeper at 300 °C than at room temperature, showing increased fatigue strength at low cycle numbers due to increasing ductility and decreased fatigue strength at increasing cycle numbers because of reduced yield strength. Cr is found to have only a negligible influence on the fatigue behaviour of Fe3Al-based alloys. Comparison between the differently processed materials shows superior LCF properties of the hot extruded iron aluminides due to significantly smaller grain sizes.

scholarly journals Study on the Prediction Method of the Ultra-Low-Cycle Fatigue Damage of Steel

2020 ◽  
Vol 10 (2) ◽  
pp. 679
Author(s):  
Qin Tian ◽  
Yanhua Liao ◽  
Xu Xie ◽  
Hanqing Zhuge
Keyword(s):  
Weld Metal ◽  
Base Metal ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Large Strain ◽  
Prediction Method ◽  
Continuum Damage Mechanics ◽  
Uniaxial Tensile ◽  
Cycle Fatigue ◽  
Strain Threshold

Cyclic void growth model (CVGM) and continuum damage mechanics (CDM) model are suitable for predicting the damage of ultra-low-cycle fatigue (ULCF) theoretically. However, studies on the prediction of ultra-low-cycle fatigue (ULCF) damage is lacking. To determine which method is better, we used the two methods to predict the damage of ULCF. Firstly, uniaxial tensile and large strain cycle tests were performed on the base metal, weld metal and heat-affected zone and the material parameters were calibrated respectively. The uniaxial plastic strain threshold and toughness parameter of weld metal were minimum, and the dispersion was maximum. The finite element models of the base metal and weld specimens were established based on the calibrated parameters, and the ULCF damage was predicted. Compared with the CVGM model, the CDM model can predict the fatigue life and the relationships among the fatigue and fracture lives, the post-fracture path and the number of cycles to initial damage. The parameter calibration is simple. CDM is superior to CVGM in predicting the ULCF damage of steel and its weld joints.

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