Investigations on weld metal chemistry and mechanical behaviour of bimetallic welds using CaO–CaF2–SiO2–Ni based electrode coatings

2016 ◽  
Vol 233 (4) ◽  
pp. 563-579 ◽  
Author(s):  
Deepak Bhandari ◽  
Rahul Chhibber ◽  
Navneet Arora ◽  
Rajeev Mehta
Keyword(s):  
Weld Metal ◽  
Nuclear Power ◽  
Welding Process ◽  
Operating Experience ◽  
Transport Systems ◽  
Low Alloy Steels ◽  
Filler Wire ◽  
Electrode Coating ◽  
Metal Chemistry ◽  
Coating Formulations

The bimetallic welds between ferritic low alloy steels and austenitic stainless steels are widely used in the heat piping transport systems of nuclear power plants for connecting the heavy section low alloy steel components with those of high temperature stainless steel pipes. The operating experience of major nuclear power plant components has recently shown that bimetallic joints can jeopardize the plant availability and safety because of increased incidences of failure. In shielded metal arc welding process, the occurrence and severity of weld defects mainly depend upon the type of electrode filler wire and the electrode coating ingredients used. The use of nickel based filler metals is no longer considered as the final solution for unexpected failures of bimetallic welds due to incidences of hot cracking. In the present paper, an attempt has been made to design and develop an intermediate electrode based on CaO–CaF2–SiO2 ternary phase diagram system and nickel as an additional electrode coating ingredient using mild steel as a filler wire for the bimetallic weld joint. The extreme vertices methodology has been used to design 21 electrode coating formulations. The quadratic regression models for weld metal chemistry, ultimate tensile strength, impact toughness, macrohardness, diffusible hydrogen content, and corrosion rate in terms of electrode coating ingredients, have been developed and checked for adequacy using analysis of variance. The work aims at studying the individual as well as combined effect of electrode coating ingredients on the measured weld responses and microstructures of the weld. Also, the electrode coating formulations suggesting multiobjective optimized solutions have been proposed.

Combining CaO–SiO2–TiO2 and CaO–SiO2–Al2O3 ternary phase systems for design of bimetallic welds

2021 ◽  
Vol 235 (8) ◽  
pp. 1271-1283
Author(s):  
Deepak Bhandari ◽  
Rahul Chhibber ◽  
Lochan Sharma ◽  
Navneet Arora ◽  
Rajeev Mehta
Keyword(s):  
Weld Metal ◽  
Power Plants ◽  
Ternary Phase ◽  
Desirability Function ◽  
Manganese Content ◽  
Research Work ◽  
Welding Process ◽  
Delta Ferrite ◽  
Electrode Coating ◽  
Phase Systems

The bimetallic welds are frequently utilized for pipeline transport system of the nuclear power plants. The occurrences of welding defects generally depend on the filler electrode as well as the electrode coatings during shielded metal arc welding process. This study involves the design of austenitic stainless steel welding electrodes for SS304L–SA516 bimetallic welds. The objective of research work includes the novel design of Al2O3–TiO2–CaO–SiO2 coatings by combining two ternary phase systems using extreme vertices mixture design methodology to analyze the effect of key coating constituents on the weld metal chemistry and mechanical properties of the welds. The significant effect of electrode coating constituent CaO on weld metal manganese content is observed which further improves the toughness of bimetallic weld joints. Various regression models have been developed for the weld responses and multi objective optimisation approach using composite desirability function has been adopted for identifying the optimized set of electrode coating compositions. The role of delta ferrite content in promoting the favourable solidification mode has been studied through microstructural examination.

Recommendations for Submerged Arc Spiral Welding With Optimized CTOD Properties

2018 ◽  
Author(s):  
Martin Liebeherr ◽  
Özlem E. Güngör ◽  
Nuria Sanchez ◽  
Hervé Luccioni ◽  
Nenad Ilic
Keyword(s):  
Weld Metal ◽  
Base Material ◽  
Welding Process ◽  
Experimental Program ◽  
Welding Parameters ◽  
Pipe Production ◽  
Filler Wire ◽  
Crack Tip Opening Displacement ◽  
Wide Range ◽  
Submerged Arc

Many pipe mills may not be familiar with a Crack Tip Opening Displacement (CTOD) requirement on the pipe seam weld, nor will they find easily relevant information in open literature. Influencing — and certainly not independent — factors are: welding parameters, base material and consumable selection. Out of these, the welding parameters such as heat input and cooling rate cannot be varied over a wide range during the pipe production, which means that the leverage is rather limited at the given welding process. The properties of the heat affected zone will be mainly affected by the base material, while the properties of the weld metal will be affected by both, base material and filler wire selection. In particular with respect to the weld metal properties it will be difficult to obtain general quantitative information. For example, a welding consumable supplier will readily provide the properties of the filler wires but would be unable to predict the changes caused by the dilution from any base material in the weld pool and specific welding procedures that may have been used. To support the pipe mills in the selection of the consumables for submerged arc welding, an experimental program was launched with the aim to provide recommendations on how to optimize CTOD toughness of the spiral weld seam. For this, a large number of welds were produced on 20 mm thick X70 coil samples, with eight different filler wire combinations, using a 2-wire (tandem) set-up for both the inside and outside weld. Welding parameters were kept constant. The welding program was applied to two different X70 steels to determine a potential influence of the micro-alloying elements, particularly Nb. The results show clearly that a careful consumable selection is required for obtaining acceptable CTOD toughness in the weld metal. Ni-Mo and Ti-B additions to the weld metal are found to be beneficial with both steel concepts. Mo addition alone both to the ID and OD welds was clearly not a suitable selection.

Operational Impacts and Consequences of Piping Component Failure: A Review of Operating Experience Data As Recorded in CODAP

2018 ◽  
Author(s):  
Braedon Carr ◽  
Bengt Lydell ◽  
Jovica R. Riznic
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Cooling Water ◽  
Operating Experience ◽  
Transport Systems ◽  
Volume Control ◽  
Operational Experience ◽  
Component Failure ◽  
Plant Safety ◽  
Operational Impacts

Water chemistry plays an important part in maintaining corrosion resistance in water transport systems throughout nuclear power plants (NPP’s). Small changes in liquid chemistry such as pH, borate concentration, or build-up of crud in reactor cooling water can result in rapid degradation or damage to components and lead to unexpected failures. The Chemical and Volume Control System (CVCS) and Reactor Water Cleanup System (RWCU) are responsible for maintaining these parameters at appropriate levels, and so failure of either of these systems can result in unnecessary stresses on many other reactor systems due to resulting transients. While the major components of these systems all have sufficient redundancy to prevent major accidents, failure of components in these systems can result in failure of other redundant components and affect plant safety [1]. The CVCS and RWCU systems have experienced aging related degradations and failures in the past, and although they have not affected the system’s emergency functions, they have resulted in unnecessary actuation of related systems, and reactor shutdowns [1]. Reactor shutdowns can result in large changes in reactor coolant chemistry such as oxygen and borate concentration transients, and the build-up of corrosion products which can’t be as easily removed during periods of reactor shutdown [2]. In the following analysis of Component Operational Experience Degradation and Ageing Program (CODAP) experience data; causes, impacts, and preventative actions as recorded in CODAP are examined for degradation events which took place in the CVCS and RWCU, of PWRs and BWRs, respectively. The analysis will demonstrate the usefulness of CODAP in examining reactor component failure trends, as well as discuss insights on improvement for the program.

Investigations on Design and Formulation of Buttering Layer Electrode Coatings for Bimetallic Welds

2016 ◽  
Vol 880 ◽  
pp. 37-40 ◽  
Author(s):  
Deepak Bhandari ◽  
Rahul Chhibber ◽  
Navneet Arora ◽  
Rajeev Mehta
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Power Plants ◽  
Welding Process ◽  
Industrial Applications ◽  
Low Alloy Steels ◽  
Shielded Metal Arc Welding ◽  
Delta Ferrite ◽  
Electrode Coating ◽  
Metal Arc Welding

The bimetallic welds (BMWs) between ferritic low alloy steels and austenitic stainless steel are used widely in steam generators of the power plants. The adoption of these welds in wide industrial applications provides feasible solutions for the flexible design of the products by using each material efficiently and economically. The present paper is an effort towards studying the development of austenitic stainless steel buttering filler material for bimetallic weld joint. The work aims at the design and development of buttering layer electrode coatings for shielded metal arc welding process using extreme vertices design methodology suggested by McLean and Anderson to study the effect of electrode coating ingredients on the buttering layer metal composition and delta ferrite content to prevent solidification cracking.

Effect of Electrode Coatings on Diffusible Hydrogen Content, Hardness and Microstructures of the Ferritic Heat Affected Zones in Bimetallic Welds

2011 ◽  
Vol 383-390 ◽  
pp. 4697-4701 ◽  
Author(s):  
Deepak Bhandari ◽  
Rahul Chhibber ◽  
Navneet Arora
Keyword(s):  
Weld Metal ◽  
Nuclear Power ◽  
Power Plants ◽  
Welding Process ◽  
The Other ◽  
Scientific Development ◽  
Shielded Metal Arc Welding ◽  
Diffusible Hydrogen ◽  
Metal Quality ◽  
Welding Electrode

Bimetallic welds (BMWs) have been a necessity within the steam generators of nuclear power plants, where the heavy section low alloy steel components are usually connected to stainless steel primary piping systems. These welds represent zones with metallurgical discontinuities, which tend to localize the strains and cause failures. The other critical issues which must be taken care of while welding of bimetallic joints include solidification cracking, thermal fatigue and residual stresses in welds. The occurrence and severity of all these problems associated with bimetallic welds depend upon the type of welding process used along with the other variables like welding consumables, heat input etc. In shielded metal arc welding (SMAW), welding electrode consumables/coatings play an important role in deciding the weld metal quality. The development of welding electrode coatings is quite difficult due to very rapid complex reactions taking place during welding and the involvement of many controlled process variables. The present paper is an effort to highlight the general issues and challenges for the systematic and scientific development of welding electrode coatings for bimetallic welds. The experimental procedure contains three sets of coated electrodes having varying ferro-alloys, silica and carbon content. In the first set of electrodes, non-ferrous elements are also introduced into the weld metal through flux addition. Further, the welded joints are subjected to various tests and then evaluated to ascertain their mechanical as well as metallurgical behaviour.

Weld Metal Chemistry of Mineral Waste Added SiO2–CaO–CaF2–TiO2 Electrode Coatings for Offshore Welds

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Waris Nawaz Khan ◽  
Rahul Chhibber
Keyword(s):  
Weld Metal ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Tio2 Electrode ◽  
Shielded Metal Arc Welding ◽  
Electrode Coating ◽  
Metal Chemistry ◽  
Metal Arc Welding ◽  
Welding Consumables ◽  
Mineral Waste

Abstract Offshore structures in recent time are witnessing the increased application of dissimilar metal welds for enhanced structural integrity. Offshore structures are complex systems. Fabrication, maintenance, and repair of these structures require conventional and advanced welding technologies along with suitably chosen welding consumables. The present work aims at the design and development of shielded metal arc welding (SMAW) electrode coating using extreme vertices design methodology. This work also attempts to study weld metal chemistry along with microstructure and microhardness. Red ochre, a mineral waste from iron ore is added in the coating composition. Multi response optimization has been carried out to obtain optimum flux composition and to study the effect of individual constituents and their interactions on the weld chemistry and microhardness.

Validity of Hardness Criteria to Demonstrate Acceptable Temper Bead HAZ Impact Properties for Nuclear Power Applications

2013 ◽  
Author(s):  
Steven L. McCracken ◽  
Richard E. Smith ◽  
Darren Barborak
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Welding Process ◽  
Impact Testing ◽  
Low Alloy Steels ◽  
Maximum Hardness ◽  
Impact Properties ◽  
Pressure Vessel Steels ◽  
Alloy Steels

Temper bead welding is used routinely for weld repair on low alloy pressure vessel steels in the nuclear power industry. Temper bead procedure qualification is contingent on demonstration that the welding process does not degrade the mechanical properties, including fracture toughness, in the base metal weld heat affected zone (HAZ). Historically for temper bead qualification acceptance, adequate HAZ properties have been verified by tensile, impact, and bend testing, while hardness criteria has not been specified. In fact, temper bead welding has been successfully applied for welding on low alloy steels without any hardness criteria for many years. In 2004, ASME Section IX added hardness testing for temper bead procedure qualification when impact testing is not required. The Eurocode, ISO standards, and numerous other European specifications include maximum hardness criteria for general welding procedure qualification and have invoked these same criteria for temper bead procedures. Test results indicate that imposing maximum hardness criteria can actually lead to acceptance of less than optimum fracture toughness in the temper bead weld HAZ due to rapidly changing microstructures in low alloy steels. Impact properties for such microstructures can vary widely even though similar levels of hardness are exhibited. This paper investigates the legitimacy of using maximum hardness criteria to demonstrate acceptable HAZ fracture toughness in low alloy pressure vessel steels.

ESTABLISHING RELATIONSHIP BETWEEN WELDING CURRENT AND WELD METAL DEPOSITION RATE FOR SOLID WIRE IN SUBMERGED ARC WELDING PROCESS

2020 ◽  
Vol 15 (2) ◽  
Author(s):  
Bashkar R ◽  
Balasubramanian V ◽  
Mani C
Keyword(s):  
Weld Metal ◽  
Deposition Rate ◽  
Arc Welding ◽  
Welding Process ◽  
Welding Current ◽  
Submerged Arc Welding ◽  
Metal Deposition ◽  
Wire Diameter ◽  
Filler Wire ◽  
Submerged Arc

Submerged Arc Welding (SAW) process is used to weld large, heavy metal deposition jobs with critical requirements, and this metal joining process alone is used to weld approximately 10% of the deposited weld metal worldwide. Any augmentation in productivity of SAW process, will immensely benefit the welding industry, as this process is widely used on variety of common metals and alloys. This paper focusses on establishing relationship between welding current and productivity (in terms of weld metal deposition rate as an index), for a given filler wire diameter. Productivity rates of most common solid filler wire sizes were studied, at different preset current values, covering full current range through bead-on-plate experiments. At each preset current value, the bead was first optimized for acceptable visual quality, by varying arc travel speed and voltage, then wire feed rate (of acceptable beads) was noted. The current density, heat input and corresponding weld metal deposition rate were calculated for establishing relationships. The established relationships can be effectively used, to estimate productivity from the preset current values, for a given solid wire diameter.

UNIFLUX VCM 125

Alloy Digest ◽  
1978 ◽  
Vol 27 (1) ◽  
Keyword(s):  
Carbon Dioxide ◽  
Fracture Toughness ◽  
Weld Metal ◽  
Heat Treating ◽  
Carbon Steels ◽  
Low Alloy Steels ◽  
Electrode Wire ◽  
Molybdenum Steel ◽  
Alloy Steels ◽  
Welding Electrode

Abstract UNIFLUX VCM 125 is a continuous flux-cored welding electrode (wire) that is used to deposit 1 1/4% chromium-1/2% molybdenum steel for which it was developed. Welding is protected by a shielding atmosphere of 100% carbon dioxide. This electrode also may be used to weld other low-alloy steels and carbon steels; however, the weld metal may differ somewhat from 1 1/4% chromium-1/2% molybdenum because of weld-metal dilution. When Uniflux VCM 125 is used to weld 1 1/4% chromium-1/2% molybdenum steel, it provides 95,000 psi tensile strength at 70 F and 24 foot-pounds Charpy V-notch impact at 40 F. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as heat treating, machining, and joining. Filing Code: SA-340. Producer or source: Unicore Inc., United Nuclear Corporation.

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