Fusion welding of steel joints is common through history of industrial applications. Among those, Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) are most common. Fusion welding process comprises of rapid heating and cooling cycles. Each cycle produces a non-uniform and transient temperature distribution and causes rapid thermal expansion followed by thermal contraction. Thus plastic deformation and thermal residual stresses can be induced in a welded joint when it cools down gradually to room temperature. In this study, temperature profiles of a hand-weld mild steel butt weld are analyzed by means of the finite element method (FEM) through ANSYS Mechanical APDL The moving heat source is simulated using the Gaussian distribution heat source model. A parametric study was then performed to evaluate the importance of certain key process parameters that affect the quality of a weldment. The effects of temperature profile on hardness numbers inside and away from the heat affected zone (HAZ) are discussed. It was found that the residual stress results obtained from the simulation agree with the distribution of hardness numbers tested on the weldment sample.
{"title":"Temperature Profile and its Effect on Hardness Numbers of a Mild Steel Butt Weld","authors":"Q. Ma","doi":"10.1115/pvp2019-93247","DOIUrl":"https://doi.org/10.1115/pvp2019-93247","url":null,"abstract":"\u0000 Fusion welding of steel joints is common through history of industrial applications. Among those, Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) are most common. Fusion welding process comprises of rapid heating and cooling cycles. Each cycle produces a non-uniform and transient temperature distribution and causes rapid thermal expansion followed by thermal contraction. Thus plastic deformation and thermal residual stresses can be induced in a welded joint when it cools down gradually to room temperature. In this study, temperature profiles of a hand-weld mild steel butt weld are analyzed by means of the finite element method (FEM) through ANSYS Mechanical APDL The moving heat source is simulated using the Gaussian distribution heat source model. A parametric study was then performed to evaluate the importance of certain key process parameters that affect the quality of a weldment. The effects of temperature profile on hardness numbers inside and away from the heat affected zone (HAZ) are discussed. It was found that the residual stress results obtained from the simulation agree with the distribution of hardness numbers tested on the weldment sample.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"71 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80409585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rebeca Hernández, M. Serrano, A. García-Junceda, E. Oñorbe, J. Vivas
The study of the enhanced creep strength of conventional ferritic-martensitic (F/M) grade 91 steel by a thermomechanical treatment (TMT) to increase the precipitation of MX particles in the matrix was performed. Creep properties were evaluated by tests at constant load at temperatures that varied from 600 °C to 700 °C with different levels of stress for both steels: T91 and T91-TMT. The creep curves and main parameters for both steels in the different conditions were analysed. Results show a great improvement of creep strength of the T91 after the thermomechanical treatment in comparison with the conventional steel. T91-TMT presents a rupture life significantly higher than T91 and a decrease of the values of the minimum creep rate. An increase of the density of MX precipitates in the matrix of the T91-TMT due to the thermomechanical treatment in comparison with T91 can be also observed. A change in the fractography was also detected. T91-TMT specimens showed signs of brittle fracture instead of the ductile fracture, with the common necking effect detected in the T91.
{"title":"Improvement of High Temperature Creep Strength of Conventional Grade 91 Steel by Thermomechanical Treatments","authors":"Rebeca Hernández, M. Serrano, A. García-Junceda, E. Oñorbe, J. Vivas","doi":"10.1115/pvp2019-93148","DOIUrl":"https://doi.org/10.1115/pvp2019-93148","url":null,"abstract":"\u0000 The study of the enhanced creep strength of conventional ferritic-martensitic (F/M) grade 91 steel by a thermomechanical treatment (TMT) to increase the precipitation of MX particles in the matrix was performed.\u0000 Creep properties were evaluated by tests at constant load at temperatures that varied from 600 °C to 700 °C with different levels of stress for both steels: T91 and T91-TMT. The creep curves and main parameters for both steels in the different conditions were analysed.\u0000 Results show a great improvement of creep strength of the T91 after the thermomechanical treatment in comparison with the conventional steel. T91-TMT presents a rupture life significantly higher than T91 and a decrease of the values of the minimum creep rate.\u0000 An increase of the density of MX precipitates in the matrix of the T91-TMT due to the thermomechanical treatment in comparison with T91 can be also observed.\u0000 A change in the fractography was also detected. T91-TMT specimens showed signs of brittle fracture instead of the ductile fracture, with the common necking effect detected in the T91.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90169555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study presents some measurements of the effective hydrogen diffusivity in a cold-rolled, Type-304 stainless steel. Steel plates rolled under various cold working (CW) ratios were prepared. Disk specimens, referred to as LT and SL specimens, were sampled from the plates to determine the diffusivity. The rolling direction is perpendicular to the thickness direction for LT specimens and parallel for the SL specimens. Fraction and distribution of α′ phase islands resulting from strain-induced martensite were characterized by electromagnetic induction (EMI) method and electron backscatter diffraction (EBSD) analysis, respectively. The diffusivity of the LT and SL specimens exposed to high-pressure hydrogen gas was determined experimentally through desorption methods. Hydrogen permeation tests for LT and SL specimens were simulated using the finite element method (FEM) by considering a model material containing an inhomogeneous distribution of α′ phase islands. The EMI measurements established that the fraction of the α′ phase increases with the CW ratio. The phase maps from the EBSD analysis revealed an important difference in α′ phase distribution on planes perpendicular and parallel to the rolling direction (LT and SL planes). For CW = 60%, the diffusivity of the SL specimen was five times larger as compared to the LT specimen, although the fraction of the α′ phase is equal. The simulation of the permeation tests also showed a strong difference in the diffusivity between both specimens, and therefore supports the experimental results. Both experiments and simulations suggested that the anisotropic nature of the effective hydrogen diffusivity (in LT and SL specimens) could be attributed to the inhomogeneous distribution of the α′ phase islands in the cold-rolled material.
{"title":"Experimental and Simulation Study on Effective Hydrogen Diffusivity of Cold-Worked Type-304 Austenitic Stainless Steel","authors":"J. Sezgin, Daichi Takatori, J. Yamabe","doi":"10.1115/pvp2019-93250","DOIUrl":"https://doi.org/10.1115/pvp2019-93250","url":null,"abstract":"\u0000 This study presents some measurements of the effective hydrogen diffusivity in a cold-rolled, Type-304 stainless steel. Steel plates rolled under various cold working (CW) ratios were prepared. Disk specimens, referred to as LT and SL specimens, were sampled from the plates to determine the diffusivity. The rolling direction is perpendicular to the thickness direction for LT specimens and parallel for the SL specimens. Fraction and distribution of α′ phase islands resulting from strain-induced martensite were characterized by electromagnetic induction (EMI) method and electron backscatter diffraction (EBSD) analysis, respectively. The diffusivity of the LT and SL specimens exposed to high-pressure hydrogen gas was determined experimentally through desorption methods. Hydrogen permeation tests for LT and SL specimens were simulated using the finite element method (FEM) by considering a model material containing an inhomogeneous distribution of α′ phase islands. The EMI measurements established that the fraction of the α′ phase increases with the CW ratio. The phase maps from the EBSD analysis revealed an important difference in α′ phase distribution on planes perpendicular and parallel to the rolling direction (LT and SL planes). For CW = 60%, the diffusivity of the SL specimen was five times larger as compared to the LT specimen, although the fraction of the α′ phase is equal. The simulation of the permeation tests also showed a strong difference in the diffusivity between both specimens, and therefore supports the experimental results. Both experiments and simulations suggested that the anisotropic nature of the effective hydrogen diffusivity (in LT and SL specimens) could be attributed to the inhomogeneous distribution of the α′ phase islands in the cold-rolled material.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"08 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81995788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Forged stainless steels are commonly used for the containment of hydrogen isotopes and fracture toughness properties are needed for structural integrity assessments. In this study, the effects of hydrogen and tritium precharging on the fracture-toughness properties of Types 316L and 304L stainless steel forgings were measured. The purpose of the study was to evaluate hydrogen and tritium effects on fracture toughness properties of: (1) Type 316 stainless steel stem-shaped and cup shaped forgings; and (2) Type 304L cylindrical block forgings with two different yield strengths. Arc-shaped fracture toughness specimens were cut from the forgings and precharged by exposing the specimens to hydrogen or tritium gas at 623K and 34.5 MPa. Tritium precharged specimens were aged at 193 K for 45 months prior to testing to build-in helium-3 from tritium decay. In the as-received condition, the J-Integral fracture toughness of the stem, cup, and block forgings were very high and exceeded 1200 kJ/m2 on average. The fracture toughness of specimens cut from the low yield strength Type 304L stainless steel block forging had the highest fracture toughness values and Type 316L stainless steel cup forging had the lowest. The reduced fracture toughness values were attributed to the large strain required to produce the cup forging and its high yield strength. Hydrogen precharging reduced the fracture toughness of the stem, cup, and block forgings to values between 34%–51% of a baseline value which was taken to be the fracture toughness value of the low yield strength block forging. Tritium precharging reduced the fracture-toughness values more than hydrogen precharging because of the effects of helium from radioactive decay of tritium. The fracture-toughness properties of tritium-precharged forgings ranged from 12% to 23% of the baseline values. In general, Type 316L stainless steel was more resistant to toughness reductions by hydrogen or tritium (and decay helium) than Type 304L stainless steel. Yield strength had only minor effects on fracture toughness for the precharged steels.
{"title":"Effect of Hydrogen Isotopes on the Fracture Toughness Properties of Types 316L and 304L Stainless Steel Forgings","authors":"M. Morgan","doi":"10.1115/pvp2019-93702","DOIUrl":"https://doi.org/10.1115/pvp2019-93702","url":null,"abstract":"\u0000 Forged stainless steels are commonly used for the containment of hydrogen isotopes and fracture toughness properties are needed for structural integrity assessments. In this study, the effects of hydrogen and tritium precharging on the fracture-toughness properties of Types 316L and 304L stainless steel forgings were measured. The purpose of the study was to evaluate hydrogen and tritium effects on fracture toughness properties of: (1) Type 316 stainless steel stem-shaped and cup shaped forgings; and (2) Type 304L cylindrical block forgings with two different yield strengths. Arc-shaped fracture toughness specimens were cut from the forgings and precharged by exposing the specimens to hydrogen or tritium gas at 623K and 34.5 MPa. Tritium precharged specimens were aged at 193 K for 45 months prior to testing to build-in helium-3 from tritium decay. In the as-received condition, the J-Integral fracture toughness of the stem, cup, and block forgings were very high and exceeded 1200 kJ/m2 on average. The fracture toughness of specimens cut from the low yield strength Type 304L stainless steel block forging had the highest fracture toughness values and Type 316L stainless steel cup forging had the lowest. The reduced fracture toughness values were attributed to the large strain required to produce the cup forging and its high yield strength. Hydrogen precharging reduced the fracture toughness of the stem, cup, and block forgings to values between 34%–51% of a baseline value which was taken to be the fracture toughness value of the low yield strength block forging. Tritium precharging reduced the fracture-toughness values more than hydrogen precharging because of the effects of helium from radioactive decay of tritium. The fracture-toughness properties of tritium-precharged forgings ranged from 12% to 23% of the baseline values. In general, Type 316L stainless steel was more resistant to toughness reductions by hydrogen or tritium (and decay helium) than Type 304L stainless steel. Yield strength had only minor effects on fracture toughness for the precharged steels.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89689292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Starting in the 1980’s, the process conditions for hydroprocessing reactors became increasingly more severe and started to exceed the economic and technically-feasible ranges for 2¼Cr-1Mo steel. Hence, new grades of reactor steels were developed to meet these demands. Reactor fabricators, steel producers, the Materials Properties Council and some refiners cautiously developed their initial applications of the new materials, with extensive testing of both the materials and fabrication methods, and restrictions to use only the most experienced, highly technical fabrication shops. The data and experience has grown exponentially since then and today, the most commonly-specified material for thick wall reactors is 2¼Cr-1Mo-¼V steel. The list of qualified fabricators worldwide has also grown, but is still limited. The purpose of this paper is to show how the industry has climbed the “learning curve,” by giving the statistics on the overall numbers of fabricated reactors (which is now over 1150), and the locations of the fabricators by country, that have been produced. Trends on the use of forgings versus plates are also included, along with the major changes over the years in the applicable ASME Codes and API standards affecting these reactors. Some of the lessons learned from past fabrication problems are also discussed along with the subsequent safeguards initiated within the industry standards.
{"title":"Industry Experience Fabricating Hydroprocessing Reactors Using 2¼ Cr-1 Mo-V Steel","authors":"C. Shargay, L. Antalffy, Kuntak Daru","doi":"10.1115/pvp2019-93229","DOIUrl":"https://doi.org/10.1115/pvp2019-93229","url":null,"abstract":"\u0000 Starting in the 1980’s, the process conditions for hydroprocessing reactors became increasingly more severe and started to exceed the economic and technically-feasible ranges for 2¼Cr-1Mo steel. Hence, new grades of reactor steels were developed to meet these demands. Reactor fabricators, steel producers, the Materials Properties Council and some refiners cautiously developed their initial applications of the new materials, with extensive testing of both the materials and fabrication methods, and restrictions to use only the most experienced, highly technical fabrication shops. The data and experience has grown exponentially since then and today, the most commonly-specified material for thick wall reactors is 2¼Cr-1Mo-¼V steel.\u0000 The list of qualified fabricators worldwide has also grown, but is still limited. The purpose of this paper is to show how the industry has climbed the “learning curve,” by giving the statistics on the overall numbers of fabricated reactors (which is now over 1150), and the locations of the fabricators by country, that have been produced. Trends on the use of forgings versus plates are also included, along with the major changes over the years in the applicable ASME Codes and API standards affecting these reactors. Some of the lessons learned from past fabrication problems are also discussed along with the subsequent safeguards initiated within the industry standards.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"334 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76396685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to achieve a better understanding of residual stress distribution characteristics associated with nozzle welds, this paper focuses on the identification of key parameters that contribute to the development of through-thickness membrane and bending components. This is because, as demonstrated in recent publications by the same authors (Song and Dong, 2016–2017), statically equivalent membrane and bending content in a given residual stress distribution play a far more critical role in fracture driving force calculation in Fitness-for-Service (FFS) assessment. To do so, a recent detailed investigation to residual stress distributions in nozzle welds is presented in this paper, covering nozzle radius to wall thickness ratio from 2 to 50, heat input from 400 J/mm to 1000 J/mm, weld joint types including set-in nozzle weld and set-on nozzle weld. By means of a residual stress decomposition technique, controlling parameters that govern through-thickness membrane and bending stresses have been identified, which are nozzle radius to wall thickness ratio (r/t) and linear heat input parameter (Q). Then, a unified functional form for representing through-thickness residual stress profile in nozzle weld is presented for supporting fitness for service assessment, e.g., by means of API 579-RP.
为了更好地了解与喷嘴焊接相关的残余应力分布特征，本文重点研究了有助于开发透厚膜和弯曲部件的关键参数的识别。这是因为，正如同一作者(Song and Dong, 2016-2017)最近发表的论文所证明的那样，在给定残余应力分布下，静等效膜和弯曲含量在FFS评估中的断裂驱动力计算中发挥着更为关键的作用。为此，本文对喷嘴焊缝的残余应力分布进行了详细的研究，包括喷嘴半径与壁厚比从2到50，热输入从400 J/mm到1000 J/mm，焊接接头类型包括喷嘴设置焊和喷嘴设置焊。通过残余应力分解技术，确定了控制透厚膜和弯曲应力的控制参数，即喷嘴半径与壁厚比(r/t)和线性热输入参数(Q)。然后，采用API 579-RP等方法，提出了一个统一的表示喷嘴焊缝透厚残余应力分布图的函数形式，以支持服役适应性评估。
{"title":"Analysis of Residual Stress Distribution Characteristics at Nozzle Weld in Pressure Vessel and Pipe Components","authors":"S. Song, P. Dong","doi":"10.1115/pvp2019-93598","DOIUrl":"https://doi.org/10.1115/pvp2019-93598","url":null,"abstract":"\u0000 In order to achieve a better understanding of residual stress distribution characteristics associated with nozzle welds, this paper focuses on the identification of key parameters that contribute to the development of through-thickness membrane and bending components. This is because, as demonstrated in recent publications by the same authors (Song and Dong, 2016–2017), statically equivalent membrane and bending content in a given residual stress distribution play a far more critical role in fracture driving force calculation in Fitness-for-Service (FFS) assessment. To do so, a recent detailed investigation to residual stress distributions in nozzle welds is presented in this paper, covering nozzle radius to wall thickness ratio from 2 to 50, heat input from 400 J/mm to 1000 J/mm, weld joint types including set-in nozzle weld and set-on nozzle weld. By means of a residual stress decomposition technique, controlling parameters that govern through-thickness membrane and bending stresses have been identified, which are nozzle radius to wall thickness ratio (r/t) and linear heat input parameter (Q). Then, a unified functional form for representing through-thickness residual stress profile in nozzle weld is presented for supporting fitness for service assessment, e.g., by means of API 579-RP.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88030861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The behavior of S420 steel under cathodic polarization in low pH aqueous environment is analyzed following the assumptions of the Theory of Critical Distances. This methodology has been successfully applied in fracture and fatigue analysis, but it has not been employed yet under stress corrosion cracking or hydrogen embrittlement conditions. This work focuses on the problem of environmentally assisted cracking by using the Point Method and the Line Method, both of them belonging to the Theory of Critical Distances. Fracture mechanic tests were carried out, using a slow strain rate machine, at two different solicitation rates (6·10−8 m/s and 6·10−9 m/s). The study is based on an experimental program composed of C(T) specimens with notch radii varying from 0 mm up to 2 mm. Cathodic polarization with a 5 mA/cm2 current has been employed and the aqueous aggressive environment was made using the Pressouyre’s method. The study has been completed with finite elements simulation analysis. The results reveal that the Theory of Critical Distances provides accurate predictions of the environmentally assisted cracking behavior of S420 steel in notched conditions.
{"title":"Analysis of Environmentally Assisted Cracking in S420 Steel by Using the Theory of Critical Distances","authors":"P. González, S. Cicero, B. Arroyo, J. Álvarez","doi":"10.1115/pvp2019-93145","DOIUrl":"https://doi.org/10.1115/pvp2019-93145","url":null,"abstract":"\u0000 The behavior of S420 steel under cathodic polarization in low pH aqueous environment is analyzed following the assumptions of the Theory of Critical Distances. This methodology has been successfully applied in fracture and fatigue analysis, but it has not been employed yet under stress corrosion cracking or hydrogen embrittlement conditions. This work focuses on the problem of environmentally assisted cracking by using the Point Method and the Line Method, both of them belonging to the Theory of Critical Distances. Fracture mechanic tests were carried out, using a slow strain rate machine, at two different solicitation rates (6·10−8 m/s and 6·10−9 m/s). The study is based on an experimental program composed of C(T) specimens with notch radii varying from 0 mm up to 2 mm. Cathodic polarization with a 5 mA/cm2 current has been employed and the aqueous aggressive environment was made using the Pressouyre’s method. The study has been completed with finite elements simulation analysis. The results reveal that the Theory of Critical Distances provides accurate predictions of the environmentally assisted cracking behavior of S420 steel in notched conditions.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85648212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Horne, Danny L. Thomas, Andrew P. S. Collett, Andrew Clay, M. Cott, A. Moffat
The prediction of welding residual stress in components is often an important input to structural integrity assessments. An efficient modelling approach was developed for predicting residual stress in power-beam welds, including validation against residual stress measurements. Specifically, sequentially coupled thermo-mechanical finite element analysis was conducted using a simplified heat source that was tuned to the observed fusion zone from a weld macrograph and thermocouple data for a series of electron beam welds in 316L austenitic stainless steel with a variety of geometries. The predicted residual stresses were compared with contour method and neutron diffraction residual stress measurements.
{"title":"An Efficient Modelling Approach for Predicting Residual Stress in Power-Beam Welds","authors":"G. Horne, Danny L. Thomas, Andrew P. S. Collett, Andrew Clay, M. Cott, A. Moffat","doi":"10.1115/pvp2019-93528","DOIUrl":"https://doi.org/10.1115/pvp2019-93528","url":null,"abstract":"\u0000 The prediction of welding residual stress in components is often an important input to structural integrity assessments. An efficient modelling approach was developed for predicting residual stress in power-beam welds, including validation against residual stress measurements. Specifically, sequentially coupled thermo-mechanical finite element analysis was conducted using a simplified heat source that was tuned to the observed fusion zone from a weld macrograph and thermocouple data for a series of electron beam welds in 316L austenitic stainless steel with a variety of geometries. The predicted residual stresses were compared with contour method and neutron diffraction residual stress measurements.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"70 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75092847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nakano Masakatsu, Tomohiro Tanaka, Masamitsu Abe, Mitsuyoshi Nakatani, H. Terasaki
Energy demand will increase due to global population growth in the future. As one of solutions for the demand, it will be necessary to operate petroleum service plants more efficiently. To improve refining efficiency, operation at higher temperatures is required of reactors used in high-pressure hydrogen service at the plants. 9Cr-1Mo-V steel has excellent creep strength compared to 2 1/4Cr-1Mo steel and 2 1/4Cr-1Mo-V steel, which have been conventionally applied to reactors, and has been already put into commercial use for boilers of thermal power plants, etc. Further application of 9Cr-1Mo-V steel is expected for reactors at petroleum refining plants. As materials applied to reactors, low-temperature toughness should be considered for weld joints in addition to creep strength. However, 9Cr-1Mo-V steel has poor low-temperature toughness compared to 2 1/4Cr-1Mo steel and 2 1/4Cr-1Mo-V steel. As for the welding methods applied to reactors, Submerged Arc Welding (SAW), Shielded Metal Arc Welding (SMAW), and Gas Tungsten Arc Welding (GTAW) can be used. The 9Cr-1Mo-V steel weld metals formed by SAW and SMAW have a high oxygen content, and their low-temperature toughness is inferior to that of the weld metal formed by GTAW. On the other hand, the GTAW weld metal has a low oxygen content and excellent low-temperature toughness. Therefore, GTAW is an effective way to improve the toughness of the weld metal. However, GTAW has low productivity compared with others, so it is necessary to apply to a narrow groove and a hot wire method to improve the productivity. In this paper, the application of narrow gap GTAW using the hot wire method was considered for welding of 9Cr-1Mo-V steel. When using the hot wire method, productivity of GTAW increases in comparison to the conventional method, leading to increased weld pass thickness. With the increase in pass thickness, the area of coarse grains increases because of decreasing thermal effect by the subsequent pass, then the low-temperature toughness decreases. Therefore, in order to improve the low-temperature toughness by refining the grains of the GTAW weld metal, the melt-run method, arc re-melting without adding fillers, was conducted after the former weld pass metal solidified. The weld metal from the melt-run method had finer grains compared with those of the weld metal without the melt-run method, and the low-temperature toughness increased. On the other hand, the melt-run method requires two processes: welding and melt-run. Therefore, a tandem electrode GTAW machine was produced in which an electrode for welding and the other one for melt-run were placed continuously to make it possible to execute welding and a melt-run without a time lag. As a result, it is possible to manufacture reactors made of 9Cr-1Mo-V steel for petroleum refining plants with sufficient low-temperature toughness by applying a welding method with narrow gap GTAW and a melt-run method combined.
{"title":"Improvement of Low-Temperature Toughness in Weld Metal Made of 9Cr-1Mo-V Steel by GTAW Method","authors":"Nakano Masakatsu, Tomohiro Tanaka, Masamitsu Abe, Mitsuyoshi Nakatani, H. Terasaki","doi":"10.1115/pvp2019-93466","DOIUrl":"https://doi.org/10.1115/pvp2019-93466","url":null,"abstract":"\u0000 Energy demand will increase due to global population growth in the future. As one of solutions for the demand, it will be necessary to operate petroleum service plants more efficiently. To improve refining efficiency, operation at higher temperatures is required of reactors used in high-pressure hydrogen service at the plants. 9Cr-1Mo-V steel has excellent creep strength compared to 2 1/4Cr-1Mo steel and 2 1/4Cr-1Mo-V steel, which have been conventionally applied to reactors, and has been already put into commercial use for boilers of thermal power plants, etc. Further application of 9Cr-1Mo-V steel is expected for reactors at petroleum refining plants. As materials applied to reactors, low-temperature toughness should be considered for weld joints in addition to creep strength. However, 9Cr-1Mo-V steel has poor low-temperature toughness compared to 2 1/4Cr-1Mo steel and 2 1/4Cr-1Mo-V steel. As for the welding methods applied to reactors, Submerged Arc Welding (SAW), Shielded Metal Arc Welding (SMAW), and Gas Tungsten Arc Welding (GTAW) can be used. The 9Cr-1Mo-V steel weld metals formed by SAW and SMAW have a high oxygen content, and their low-temperature toughness is inferior to that of the weld metal formed by GTAW. On the other hand, the GTAW weld metal has a low oxygen content and excellent low-temperature toughness. Therefore, GTAW is an effective way to improve the toughness of the weld metal. However, GTAW has low productivity compared with others, so it is necessary to apply to a narrow groove and a hot wire method to improve the productivity.\u0000 In this paper, the application of narrow gap GTAW using the hot wire method was considered for welding of 9Cr-1Mo-V steel. When using the hot wire method, productivity of GTAW increases in comparison to the conventional method, leading to increased weld pass thickness. With the increase in pass thickness, the area of coarse grains increases because of decreasing thermal effect by the subsequent pass, then the low-temperature toughness decreases. Therefore, in order to improve the low-temperature toughness by refining the grains of the GTAW weld metal, the melt-run method, arc re-melting without adding fillers, was conducted after the former weld pass metal solidified. The weld metal from the melt-run method had finer grains compared with those of the weld metal without the melt-run method, and the low-temperature toughness increased. On the other hand, the melt-run method requires two processes: welding and melt-run. Therefore, a tandem electrode GTAW machine was produced in which an electrode for welding and the other one for melt-run were placed continuously to make it possible to execute welding and a melt-run without a time lag. As a result, it is possible to manufacture reactors made of 9Cr-1Mo-V steel for petroleum refining plants with sufficient low-temperature toughness by applying a welding method with narrow gap GTAW and a melt-run method combined.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73675634","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Residual stresses resulting from welds are a key consideration in the design and assessment of piping and pressure vessels. As welding is a variable process, the resulting variability in weld residual stress should be accounted for in design and assessment. This paper investigates the variability in residual stress resulting from flux cored arc welds by performing residual stress measurements on a set of nominally identical welds between 25mm plates of grade DH36 steel. The welds were produced in two environments to assess the impact on residual stress variability: a well-controlled laboratory environment and a less controlled factory environment. The results showed significant variability in the residual stresses between the welds, with standard deviations up to 25% of the peak value in some locations near the weld center. The welds were two sided and higher variability was measured in the side performed second, with the variability in heat applied appearing to be a key driver of the residual stress variability. A difference was observed between the standard deviations of residual stress in the factory and laboratory samples, with the laboratory samples showing less residual stress variability. Whilst the small number of samples measured prevents firm quantitative conclusions being drawn about the potential differences in residual stress variability between production environments the results do suggest that there is value in further study.
{"title":"The Variability in Weld Residual Stress","authors":"H. Cathcart, G. Horne, A. Moffat","doi":"10.1115/pvp2019-93562","DOIUrl":"https://doi.org/10.1115/pvp2019-93562","url":null,"abstract":"\u0000 Residual stresses resulting from welds are a key consideration in the design and assessment of piping and pressure vessels. As welding is a variable process, the resulting variability in weld residual stress should be accounted for in design and assessment. This paper investigates the variability in residual stress resulting from flux cored arc welds by performing residual stress measurements on a set of nominally identical welds between 25mm plates of grade DH36 steel. The welds were produced in two environments to assess the impact on residual stress variability: a well-controlled laboratory environment and a less controlled factory environment.\u0000 The results showed significant variability in the residual stresses between the welds, with standard deviations up to 25% of the peak value in some locations near the weld center. The welds were two sided and higher variability was measured in the side performed second, with the variability in heat applied appearing to be a key driver of the residual stress variability. A difference was observed between the standard deviations of residual stress in the factory and laboratory samples, with the laboratory samples showing less residual stress variability. Whilst the small number of samples measured prevents firm quantitative conclusions being drawn about the potential differences in residual stress variability between production environments the results do suggest that there is value in further study.","PeriodicalId":23651,"journal":{"name":"Volume 6B: Materials and Fabrication","volume":"108 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79400522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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