Weld Overlays Research Articles

Effects of heat input on the pitting resistance of Inconel 625 welds by overlay welding

The objective of this study was to establish the relationship between the dilution ratio of the weld zone and pitting resistance depending on the heat input to welding of the Inconel alloy. Each specimen was produced by electroslag welding using Inconel 625 as the filler metal. In the weld zone of each specimen, dendrite grains were observed near the fusion line and equiaxed grains were observed on the surface. It was also observed that a melted zone with a high Fe content was formed around the fusion line, which became wider as the welding heat input increased. In order to evaluate the pitting resistance, potentiodynamic polarization tests and CPT tests were conducted. The results of these tests confirmed that there is no difference between the pitting resistances of each specimen, as the structures of the surfaces were identical despite the effect of the differences in the welding heat input for each specimen and the minor dilution effect on the surface.

원전 가압기 히터슬리브 J-Groove 이종금속 용접부 보수를 위한 용접 공정변수 최적화에 관한 연구

This study was performed to develop repair technology for J-Groove dissimilar metal weld of pressurizer heater sleeve in nuclear power plants. Pad, J-Groove automatic welding and mechanical machining equipments to develop repair technology using `Half Nozzle Repair` were designed and manufactured. To obtain the optimum welding process parameters during Pad temperbead overlay welding, several welding experiments using Taguchi method were conducted. Weldability of Pad overlay weld specimens was estimated by PT/RT test, FE-SEM, EDS and Vickers hardness test. Also, J-Groove welding to adjust weld shape conditions requiring in ASME Code was carried out and its integrity of weld specimens was evaluated through PT/RT test and optical microscope. Consequently, it was revealed that Pad and J-Groove overlay welding for dissimilar metal weld of pressurizer heater sleeve could be possible to meet Code standard without weld defect.

원자력발전 설비의 소재와 용접방법에 대한 최신 기술동향

Recent developing tendency of nuclear power plant are studied by searching of NDSL, KIPRIS, Science Direct and so on. Welding materials such as low alloyed steels, stainless steels, nickel-based alloys, zirconium alloy and welding methods such as narrow gap welding, laser beam welding, friction stir welding, overlay welding are investigated.

Welding Parameters for Inconel 625 Overlay on Carbon Steel using GMAW

Nickel chromium molybdenum alloys are well known for its creep properties along with high corrosion resistance which finds a very large application in Oil and Petro chemical industries. However due to its prohibitive cost a cheaper alternative of cladding Ni alloys on carbon steel base material is widely used. The Ni alloy may be applied by different methods such as roll bonding, explosive cladding or by weld overlaying. As the weld overlay process is simple and requires a small set up, this is being widely used to improve the corrosion properties of various equipments used in Oil and Petro chemical industries. While the process is simple and easier to apply, enough care need to be applied in controlling the weld chemistry. The most critical element to control is the Fe content in the weld overlay. It is observed that the corrosion properties are not affected when the Fe content is restricted to below 5%. Effort is made in this study to apply the weld overlay using Gas metal arc welding process using soild Inconel 625 wire. Various properties such as chemical composition, cracking tendencies, hardness across the weld overlay area etc were also studied in this work.

Heat treatment of steel–TiC composite materials produced by overlay laser welding

The effect of heat treatment (ageing) on the microstructure and property of SPN14A7M5/TiC materials produced by overlay laser welding has been studied. The optimum conditions of ageing are found.

Structure Formation and Properties of Weld Overlay Produced by Laser Cladding under the Influence of Nanoparticles of High-melting Compounds

Researches of flat samples using laser cladding technology were carried out. Nickel-based powders with the addition of nanopowders of tantalum carbide and tungsten carbide with water-based hydroxyethylcellulose as the binder, were used for slip cladding. Powders are fused on under local argon protection. The experiments were carried out to determine minimal base metal penetration depth, microhardness distribution over cross section of substrate and deposited layers, enrichment level of cladding metal with base components depending on power density and deposition rate. Metallographic studies of obtained overlays were conducted using a high-precision analytical equipment.

Fatigue behavior of laser clad round steel bars

Laser cladding is an overlay welding method to manufacture high performance, fusion bonded metal, and metal matrix composite coatings on metallic substrates with low dilution. Owing to steep thermal gradients, rapid solidification, and possible mismatch in coefficients of thermal expansion between the coating and the substrate, laser cladding induces large tensile residual stresses in coating layer, potentially affecting the service life of clad component under external load-induced stresses. In this study, four-point bending and torsion fatigue tests were conducted on relatively large round laser clad steel bars to determine the effect of laser cladding on fatigue strength. Quenched and tempered 42CrMo4 steel clad with Inconel 625 and S355 structural steel clad with Stellite 21 were subjected to various stress levels for relatively large number of cycles with and without postweld heat treatment (PWHT). The results indicated that Stellite 21 decreased the fatigue life of S355 at all the applied loads, whereas Inconel 625 increased the fatigue life of 42CrMo4 at high loads but decreased at low loads. Applied PWHT did not show any positive influence on fatigue life.

Minimização de defeitos em revestimentos de superligas de níquel depositada pelo processo TIG com alimentação de arame frio

O objetivo do presente trabalho foi avaliar a influência dos parâmetros de soldagem na formação de defeitos na soldagem de revestimentos com ligas à base de níquel, e sua possível eliminação através do correto ajuste dos referidos parâmetros. Para tanto, foram depositados revestimentos com as ligas à base de Ni do tipo Inconel 625, Hastelloy C276 e Inconel 686, sobre um substrato de aço C-Mn, através do processo TIG com alimentação de arame frio. O planejamento dos experimentos foi realizado aplicando-se o método Taguchi. Os fatores de controle avaliados foram a Técnica da energia (TE), o nível de energia de soldagem (E), o tipo de liga (L), o gás de proteção (G) e o tipo de tecimento (T). Outros parâmetros foram mantidos constantes, tendo sido investigados previamente. Os resultados mostraram que o tipo de tecimento em espiral, embora contribua significativamente para a redução da diluição, causa uma forte instabilidade ao processo, resultando na maioria dos casos em defeitos superficiais ou defeitos entre passes. A condição ótima para evitar a formação de defeitos entre passes identificada pelo método Taguchi foi constituída pelas seguintes combinação de fatores de controle 2-2-2-3-3, ou seja: TE-I; Emédia; Liga Hastelloy C276; Gás de proteção Ar+He; Tecimento Duplo-8. A condição ótima para a soldagem sem defeitos resulta em alto nível de diluição não sendo indicada para a soldagem de revestimentos resistentes à corrosão.

Fatigue life assessment of railway rail subjected to welding residual and contact stresses

Even though repair welding has been adopted as a useful remedial technique for railway rail, cracks were found beneath the weld layer under wheel-to-rail contact conditions. In the present study, lifetime assessment of a typical railway rail subjected to both welding residual and contact stresses is carried out to resolve this issue; A finite element method to predict the residual stress was established by taking into account the in-situ overlay welding process and applied for the rail with different welding depths to examine optimum weld geometry as well as failure causes. Subsequently, the contact stress during a wheel rolled over the weld was calculated and combined with the residual stress for fatigue damage assessment. The residual stress was reduced as the increase of the welding depth so that sufficient grinding before the overlay process will be beneficial to prevent unanticipated failure and the combined stress should be considered for accurate fatigue life assessment of the overlay-welded railway rail.

Microstructure and Microsegregation of an Inconel 625 Weld Overlay Produced on Steel Pipes by the Cold Metal Transfer Technique

Abstract The aim of this work was to investigate the development of microstructure and variations in chemical composition in commercial Inconel 625 coatings on a ferritic-pearlitic steel overlaid by the CMT method.The investigation showed that microsegregation occurring during the weld overlay solidification makes the dendrite cores to be richer in Ni, Fe and Cr and in the between dendrite arms in Mo and Nb. Niobium shows the strongest tendency to segregation during solidification; molybdenum tends to segregate less and chromium has the lowest tendency to segregation. Although Inconel 625 is a solid solution strengthened alloy, Nb and Mo-rich phases are formed in the between dendrite arms of weld overlays.

Mechanical Property and Corrosion Resistance of the E309L Buffer Layer in Weld Overlay

The weld overlay technology of high strength low alloy steel (HSLA) and austenitic stainless steel is widely applied in such fields as petroleum, chemical industry and energy, and its service environment is of high temperature and corrosion. As the matching performance is often poor for both austenitic stainless steel and high strength low alloy steel, cavities and crackles occur easily at the joints, which cause brittle fractures with dangerousness to some extent. So in the present study, the metal-inert gas welding (MIG) is used to clad the austenitic stainless steel to HSLA. In the experimental group, 4mm buffer layer (E309L) and 8mm cladding layer (E347L) were successively cladded on the substrate (Q345B), while 12mm cladding layer was directly deposited on the substrate in the control group. The hot corrosion tests were done, and through the scanning electron microscope (SEM), we observed the cross-sectional morphology. By the X-ray diffraction (XRD), we analyzed ingredients of the corrosion products. The corrosion products in the experimental group mainly consist of iron and nickel oxides, while the products are mainly iron complex compound and salt in the control group. The SEM results show the area near the welding seam of the specimens without buffer layer had been corroded severely. However, only a slight corrosion occurs adjacent to the welding seam. This demonstrates that the buffer layer can protect the specimens from being corroded.

Study on the Manufacturing Technology of Directly Metal Forming Based on Overlay Welding

Rapid prototyping technology can greatly improve the actual processing industrial prototype; this paper introduces the main principle, characteristics and technology of rapid prototype manufacturing. The current rapid prototype manufacturing products and production problems are analyzed. Because of the direct metal forming process have the characteristic of point by point, surfacing with stack molding manufacturing layer by layer, so it is suitable for complex shape parts two-dimensional or three-dimensional functionally gradient materials manufacturing.

Characterization of <i>In Situ</i> Synthesized TiC-TiB<sub>2</sub> Reinforced Fe Matrix Wear-Resistant Coating by TIG Arc/Cored-Wires Weld Overlaying Technology

TiC-TiB2/ Fe matrix composite coatings were in-situ synthesized in the surface of Q235 steel substrate by TIG/cored-wire weld overlaying. The microstructure, micro-hardness and wear resistance of the weld overlay coating were investigated using SEM, XRD, Micro-hardness Tester and Pin-disc Wear Tester respectively. The results showed that the weld overlay coating presented a dense microstructure with defect-free of pore and crack, and better metallurgical bond with the substrate; TiC and TiB2 particulate distributed dispersively in Fe matrix of the weld overlay coatings. The highest Micro-hardness of the weld overlaying was 1657.58HV, which is 6 times higher than the substrate, and wear resistance are also improved at the room temperature under normal atmosphere conditions.

Trends in Development of Weld Overlaying During The 21ST Century

Abstract The present article discusses the trends in the development of welding and weld overlaying on the threshold of the new millennium and during it. It presents the trends in the production of welding materials for welding and weld overlaying in industrially developed and developing countries. The structure of welding methods is also shown, giving priority to its development until 2020.

Further Understanding of Furnace Wall Corrosion in Coal-Fired Boilers

A comprehensive low-NOx corrosion study consisting of pilot-scale combustion testing and laboratory retort exposure was performed. From the pilot-scale testing, the gas and deposit compositions in the lower furnace of utility boilers burning eight U.S. coals with a wide range of sulfur and chlorine contents were determined. These combustion conditions were then closely reproduced in a series of 1,000 h laboratory corrosion tests to evaluate the materials performance of different furnace-wall alloys and weld overlays at 399, 454, and 510°C (750, 850, and 950°F). Results of the laboratory study indicate that a typical dual-layered scale was formed on the metal surface from simultaneous oxidation/sulfidation due to the presence of sulfur in coal. A new corrosion mechanism is proposed here as “active sulfidation” to account for the accelerated corrosion attack on furnace walls resulting from the presence of chlorine in coal. The mechanism involves the conversion of iron sulfide (FeS) in the corrosion scale to...

Simulation and Measurement of Through–Wall Residual Stresses in a Structural Weld Overlaid Pressurizer Nozzle

Full structural weld overlays (FSWOLs) have been used extensively as a repair/mitigation technique for primary water stress corrosion cracking in pressurizer nozzle dissimilar metal (DM) welds. To support an approved FSWOL design and safety submission for British Energy pressurized water reactor (PWR) nozzles, an in-depth evaluation was performed to assess the effects of a FSWOL on the through wall residual stress distribution in safety/relief pressurizer nozzles. Two safety/relief pressurizer nozzle mockups were fabricated based on British Energy’s PWR nozzle design. One mockup included the nozzle to safe-end DM weld and the safe-end to stainless steel weld, while the second mockup included the DM weld, the stainless steel weld, and a Westinghouse designed structural weld overlay. The mockups were fabricated utilizing materials and techniques that represented the plant specific nozzles as closely as possible and detailed welding parameters were recorded during fabrication. All welds were subsequently nondestructively evaluated (NDE). A thorough review of the detailed fabrication records and the NDE results was performed and several circumferential positions were selected on each mockup for subsequent residual stress measurement. The through wall residual stress profiles were experimentally measured through the DM weld centerline at the selected circumferential positions using both the deep-hole drilling (DHD) and incremental deep-hole drilling (iDHD) measurement techniques. In addition to experimental residual stress measurements, the through-wall residual stress profiles were simulated using a 2D axisymmetric ansys™ finite element (FE) model. The model utilized the application of temperature constraints on the weld elements to simulate the thermal welding cycle which greatly simplified the simulation as compared with detailed heat source modeling methods. Kinematic strain hardening was used for material modeling of the weld and base metals. A range of residual weld stress profiles was calculated by varying the time at which the temperature constraints were applied to the model. The simulation results were compared with the measurement results. It was found that the effects of the FSWOL were principally threefold. Specifically, the FSWOL causes a much deeper compressive stress field, i.e., the overlay shifts tension out toward the outside diameter (OD) surface. Furthermore, the FSWOL reduces tension in the underlying dissimilar metal weld, and finally, the FSWOL causes higher peak compressive and tensile residual stresses, both of which move deeper into the nozzle wall after the overlay is applied. Relatively good agreement was observed between the FE results and the measurements results.

Hydrogen embrittlement of a bimaterial

Commonly, within the energy industry, the corrosion resistance of pressure vessel steels is increased by the addition of an overlay coating comprising a nickel-based alloy or a stainless steel. However, the interface between the two alloys is prone to hydrogen-assisted cracking, due to for example carbide precipitation near the interface. In the present study, the sensitivity of the tensile strength of the interface to hydrogen concentration is measured for both notched and un-notched specimens made from the overlay welding of 690 nickel alloy on a low alloy steel A533B. An elastic–plastic finite element analysis is used to determine the stress and strain state near the notch root, and thereby to calculate the local distribution of hydrogen within the lattice and at traps. The observed strength of the notched specimens is best rationalised by assuming that the local cohesive strength of the interface is a function of the lattice hydrogen concentration, with a negligible influence of the trapped hydrogen. The scatter in specimen strength, and the relative strength of the notched and un-notched specimens, are adequately described by Weibull statistics, with a low value of Weibull modulus equal to 3.4.

Optimization of weld pitch on overlay welding using mathematical method

It is important to overlap the even bead continuously to automate the overlay welding process. To obtain the even surface bead on overlay welded product, optimization of pitch distance between the each pass is one of the methods. Therefore, this study determines the optimal second pass pitch distance with respect to welding parameter such as torch position and welding speed. Variety of welding experiments was carried out with different welding parameters using Central Composite Rotatable Design (CCRD) method. Based on the experimental results, empirical models were developed after analyzing correlation between welding parameters and bead height, width and decentration of overlay welding. Finally, optimized empirical models were developed for predicting bead height and width by analyzing the main effect of each factor which affects bead geometry and their influence on interaction. In addition, a mathematical model was developed which determines the bead profile for visualizing the bead shapes using the Matlab curve fitting tool. These two models were combined for one of the overlay bead shape model. Furthermore, the mathematical model is then used to determine the second pass pitch distance, by allowing the same area above and below the point of interaction between two overlay weld pass.

직선형 프로세스 파이프 내면 오버레이 GTAW 용접시스템 개발

In this research, GTA overlay welding system is developed for inside of straight pipes in various diameter. It can be applied to oil, ship building and plant industry, especially pipes connected to pressure vessels, for the purpose of cost reduction by cladding inside of pipes with corrosion and heat resistant alloys such as stainless steel or Inconel. Developed system consists of GTA power source, torch, wire feeding system, automatic arc length adjusting device, CCD camera and cooling unit. Two types of pipe inside overlay welding system are developed. One is for maximum 3m pipe length with 3 inch ~ 12 inch pipe outer diameter. Another type can be applied to maximum 12m pipe length with 7 ~ 24 inch OD. Developed system successfully produced inside cladded pipe and the results are shown through cross sectional images of the pipes.

Residual stress reduction in the penetration nozzle weld joint by overlay welding

Stress corrosion cracking (SCC) in the penetration nozzle weld joint endangers the structural reliability of pressure vessels in nuclear and chemical industries. How to decrease the residual stress is very critical to ensure the structure integrity. In this paper, a new method, which uses overlay welding on the inner surface of nozzle, is proposed to decrease the residual stresses in the penetration joint. Finite element simulation is used to study the change of weld residual stresses before and after overlay welding. It reveals that this method can mainly decrease the residual stress in the weld root. Before overlay welding, large tensile residual stresses are generated in the weld root. After overlay weld, the tensile hoop stress in weld root has been decreased about 45%, and the radial stress has been decreased to compressive stress, which is helpful to decrease the susceptibility to SCC. With the increase of overlay welding length, the residual stress in weld root has been greatly decreased, and thus the long overlay welding is proposed in the actual welding. It also finds that this method is more suitable for thin nozzle rather than thick nozzle.