Root Bead Research Articles

Monitoring of root gap change based on electrical signals of flux-cored arc welding using random convolution kernel transform

A monitoring technique for detecting changes in the root gap of butt joints during the flux-cored arc welding (FCAW) was proposed. FCAW experiments were conducted for both increasing and decreasing root gap conditions, and current and voltage were measured during the root-pass welding. The measured time series signals were used as input data for training Random Convolution Kernel Transform (ROCKET) algorithm, which consists of a feature extractor with multiple random kernels, and a linear classifier. A univariate model using current and voltage, respectively, and a multivariate model using both were compared, and the multivariate model showed the highest classification accuracy of 96.2%. Moreover, the classification errors were investigated by correlating the geometry of the root bead with the measured signals.

Fatigue Strength Assessment of Single-Sided Girth Welds in Offshore Pipelines Subjected to Start-Up and Shut-Down Cycles

During the service life of offshore pipelines, many start-up and shut-down cycles take place, possibly leading to significant cyclic loads. Fatigue failure may occur, resulting in serious environmental pollution and loss of property. The study aims to assess the fatigue strength of single-sided girth welds in offshore pipelines under these specific fatigue loads. The longitudinal stress range caused by the variation of the pipeline’s internal pressure and temperature is calculated. The effective notch strain approach is used to assess the fatigue strength of welds. The plastic behaviour of the weld root is investigated for a study case to justify the use of low-cycle fatigue assessment approaches. The effect of weld root geometry on the notch stress factor is studied to identify the dominant geometrical parameters. The fatigue strength of the study case is assessed, and some limitations of the assessment are discussed. The results show that the plastic behaviour of the weld root is only significant for severe local stress concentrations, which is mainly governed by the axial misalignment, weld root angle and the weld root bead width. If the fatigue damage at failure is 0.1, a limited number of start-up and shut-down cycles are allowed during the service life of the pipeline for the study case, indicating the necessity of fatigue strength assessment.

Magnification Factor Mk and its Parametric Solutions for Fatigue Crack Growth Assessment of Flaws at Weld Root Toes in Girth Welds

Abstract To account for the effect of the stress concentration factor (SCF) at the weld toe on stress intensity factor range ΔK, a magnification factor Mk is used. The existing Mk solutions given in BS 7910 were developed for the fatigue assessment of flaws at the toes of fillet and butt welds and may not be suitable for assessing flaws at single-sided girth weld root toes, where fatigue cracking often initiates and the weld width is relatively small. Finite element (FE) modeling was performed to determine a 2D Mk solution for engineering critical assessment (ECA) of a flaw at the weld root bead toe. The weld root bead profile was uniquely characterized by five variables including weld root bead width, weld root bead height, hi-lo, weld root bead angle, and weld root bead radius. Following a parametric sensitivity study, defect size, weld root bead height, and hi-lo were identified as the governing parameters. A total of 6000 FE simulations was performed, covering different combinations of weld root bead height and hi-lo. A series of automation scripts were developed in the python programming language and the Mk solution for each type of defect model was developed and provided in a parametric equation. The accuracy of the 2D Mk solutions was confirmed by the experimental data. It was found that the methods and Mk solutions currently recommended in BS 7910 and DNVGL-RP-F108 are inappropriate for assessing a flaw at a girth weld root toe.

Aumento de calidad en uniones soldadas de estructuras de paredes delgadas mediante modelo de simulación

El módulo de cálculo de simulación y el paquete de software solidworks han ayudado a definir la forma y las dimensiones óptimas de uniones soldadas simples que pueden servir de base para calcular los parámetros de proceso de soldadura. Habiendo comparado los modelos con diferentes secciones transversales de soldadura, el autor ha determinado que la altura y el ancho de la soldadura no afectan significativamente la concentración de tensión, y la concentración y el valor de la tensión dependen principalmente de la forma del latido de la raíz y del punto de separación entre las partes soldadas.

Experimental Research on the Electrical Parameters of GMAW on Different Positions Welds

This paper presents the influence of the main parameters of the GMAW welding process on ingot iron sized 300 × 125 × 3 mm3, with a 1 mm separation between edges and without any bevel preparation. Three gases were used in this research: CO2, C15 and C25, with the purpose of studying the shielding influence of each of these gases separately in the welding process. In this research different power ranges were used with the purpose to assure the quality of the surface finish on the bead and the minimum penetration on the plates. The influence of the welding torch’s direction of advancement (forehand or backhand) for positions PA, PC and PE were studied together with its influence on the power source. The position which needed the least energy was the PA, followed by position PC and then position PE. The forehand advancement direction required more power than the backhand advancement direction for all positions. The influence of the gases from high to low on the width of the root bead and face bead was C15, CO2 and C25. This work would be useful to evaluate the influence of the welding parameters on a welding procedure specification with the GMAW welding process.

The Use of Fiberglass and Ceramic Cylinders to Support the Root Pass in C-Steel Welds with a Double-V Groove

Abstract The aim of this work is to evaluate the effectiveness of fiberglass and ceramic fiber cylinders as root-pass weld backing for a double-V groove in 16 mm-thick carbon steel. Three different cylinder diameters were tested: 4.8, 9.5 mm (fiberglass) and 6.4 mm (ceramic fiber). The welding process used was GMAW. The welding technique and the following process variables were investigated: root opening, current and travel speed. The results show that cylindrical fiberglass and ceramic fiber backings not only have excellent refractory properties, but also seal the root opening and contain the weld pool sufficiently to produce a root bead free of discontinuities and with a satisfactory shape and geometry. Working points were defined, together with a possible operating range for the welding parameters. It was concluded that cylindrical fiberglass and ceramic fiber weld backings hold great promise for use in root-pass welds in double-V grooves in applications in the naval and metallurgical industry.

Efeito do Tratamento Térmico de Solubilização e Estabilização Convencional e Alternativo na Microestrutura de uma Junta Soldada com Aço Inox 347

Este trabalho estuda a microestrutura formada na zona termicamente afetada (ZTA) e na zona fundida (ZF) de uma junta soldada pelo processo TIG automático no passe de raiz, processo plasma nos passes de enchimento e soldagem SAW para os passes de acabamento em junta de topo com chanfro “V” simples, usando o aço inoxidável austenítico AISI 347. Foram estudadas as condições: como soldada; após tratamento térmico convencional de solubilização a 1060 °C e estabilização a 900 °C; e após tratamento térmico alternativo, onde a peça foi solubilizada a 1060 °C e mantida no forno que foi resfriado até 900 °C para a estabilização. Os resultados mostram que, na condição como soldado houve crescimento de grão na ZTA e a ZF apresentou 13% de ferrita �� com diferentes morfologias, tendo sido observada a precipitação de carbetos de Cr e de Nb. Após o tratamento térmico convencional de solubilização e estabilização, foi observada uma diminuição significativa do teor de ferrita �� na ZTA e na ZF, tendo sido observados carbetos de Nb e Cr, distribuídos de forma mais dispersa e com tamanhos menores, que contribuem para minimizar a possibilidade de ocorrer o fenômeno da sensitização. Após tratamento térmico alternativo de solubilização e estabilização, a microestrutura da ZTA e ZF foi similar à obtida no tratamento convencional, sendo que o teor de ferrita δ na ZF foi ainda mais reduzido, de 4,5%. Foi concluído que o tratamento térmico alternativo de solubilização e estabilização foi tão eficaz quanto o tratamento térmico convencional para a adequação da microestrutura da junta soldada, com uma significativa vantagem do tratamento térmico proposto em reduzir o tempo e o custo desta operação.

Effect of geometric construction on residual stress distribution in designing a nuclear rotor joined by multipass narrow gap welding

The purpose of this study is to investigate the effect of geometric construction on the distribution of residual stresses before and after heat treatment in designing a nuclear welded rotor. The local material removal method was used to measure internal residual stress of the experimental pipe after post weld heat treatment. Three finite element models were employed as follows: a model of experimental pipe, a model with a bottom protrusion existed at the weld region, and a model of two rotor discs butt-welded with a bottom protrusion at the weld region. Investigated results showed that the bottom protrusion existed at the weld region can decrease the residual stress and mitigate the stress evolution significantly on the inner surface. Under the binding effect of the rotor discs, the axial stress of inner surface region is compressive stress; the through-wall axial stress at the weld center line can be deemed to a bending type; both the hoop stress and axial stress at the weld center line on the inner surface are compressive. The impact of geometric construction on the stress evolution at the root bead begins after pass 15 deposited.

One-sided welding with cordierite ceramic backing

This paper presents an evaluation of welded joints using ceramic backing produced in the laboratory. The one-sided welding technique was used to weld A-36 steel plate with 6.4 and 15.8 mm thicknesses by employing the GMAW process. With the 6.4 mm steel plate, only the root bead welded over the ceramic backing was evaluated. With the 15.8 mm steel plate, a multipass welded joint was made. After welding, the welded joints were submitted to visual inspection, dye penetrant, macrograph, Vickers microhardness, optical microscopy, bending and tensile testing and chemical analysis using non-destructive test. The results show that the root pass made over the ceramic backing presented adequate shape, free from discontinuities, with adequate penetration in the edges of the groove and adequate reinforcement. With regard to the welded joint, the microstructure of the fusion zone presented predominance of primary ferrite, consisting of grain boundary ferrite and polygonal ferrite, and ferrite with an aligned second phase. The Vickers microhardness obtained mean values below 180 VH both in the heat affected zone and the fusion zone. Bending tests did not show discontinuities greater than 3 mm and in the tensile tests, the rupture occurred in the base metal, indicating that the welding procedure was adequate. The chemical composition of the inclusions both in the root pass and in the last weld bead have the same constituents, despite different proportions, indicating that there was no contamination of the ceramic backing material into the weld bead.

The effect of PURGING GAS on 308L TIG root pass FERRITE CONTENT

Argon is commonly used as root shielding gas in TIG-welding of stainless steels. As argon world-wide is in short supply and prices are rising, it is of interest to investigate what effects changing to alternative root shielding gases might have on weld metal microstructure. Manual TIG welding was used for root and hot pass welding in 304L pipe and plate material using Ar2 as shielding gas and Ar2, N2+10%H2 or N2 as root shielding gas. A significant increase in the nitrogen content of root beads was found when changing the root shielding gas from pure argon to a nitrogen-rich gas. Typically the root bead nitrogen content increased from 500–600 ppm for argon shielding to 1 100 ppm with nitrogen as root shielding gas. As a result the ferrite content decreased with up to 5 FN from about 8–9 FN to 3–5 FN. However, no indication of hot cracking was found and all root beads solidified as predicted by the WRC-92 diagram with ferrite as the leading phase. It is suggested that typical 304L steel and 308L consumable compositions will permit use of nitrogen-rich gases for root shielding without a significantly increased risk of hot cracking. However, the increased nitrogen level must be considered in the choice of steel and consumable. It is advised to use the WRC-92 diagram to make sure there is sufficient safety margin for actual compositions and, if possible, check root bead ferrite content.

Soldagem unilateral com suporte cerâmico de cordierita

Este trabalho apresenta a avaliação de juntas soldadas com suporte cerâmico de cordierita produzido em laboratorio. Foi utilizada a técnica de soldagem unilateral em chapas de aço A-36 com espessuras de 6,4 e 15,8 mm pelo processo MIG-MAG. Com a chapa de 6,4 mm foi avalliado apenas o passe de raiz sobre o suporte cerâmico. Com a chapa de 15,8 mm foi produzida uma junta soldada em passes múltiplos. Após soldagem as juntas soldadas foram submetidas a ensaios de inspeção visual, liquido penetrante, macrografia, microdureza Vickers, microscopia ótica, ensaios de dobramento e de tração e análise química por EDS. Os resultados mostram que o passe de raiz, realizado sobre o suporte cerâmico, apresentou bom acabamento, isento de descontinuidades, com penetração adequada nas laterais do chanfro e reforço de solda apropriado. Em relação à junta soldada, a microestrutura da zona fundida (ZF) obteve predominância de ferrita primária, em suas formas de ferrita de contorno de grão e poligonal, e ferrita com segunda fase alinhada. A microdureza Vickers obteve valores médios abaixo de 180 HV tanto na zona termicamente afetada (ZTA) como na ZF. Os ensaios de dobramento não apresentaram descontinuidades maiores que 3 mm e nos ensaios de tração a ruptura ocorreu no metal base, indicando que o procedimento de soldagem foi adequado. A composição das inclusões tanto do passe de raiz como do ultimo passe de solda possuem os mesmos constituintes, apesar de proporções diferentes, indicando que não houve contaminação do material do suporte cerâmico no cordão de solda.

Soldagem unilateral com suporte cerâmico de cordierita

Este trabalho apresenta a avaliação de juntas soldadas com suporte cerâmico de cordierita produzido em laboratorio. Foi utilizada a técnica de soldagem unilateral em chapas de aço A-36 com espessuras de 6,4 e 15,8 mm pelo processo MIG-MAG. Com a chapa de 6,4 mm foi avalliado apenas o passe de raiz sobre o suporte cerâmico. Com a chapa de 15,8 mm foi produzida uma junta soldada em passes múltiplos. Após soldagem as juntas soldadas foram submetidas a ensaios de inspeção visual, liquido penetrante, macrografia, microdureza Vickers, microscopia ótica, ensaios de dobramento e de tração e análise química por EDS. Os resultados mostram que o passe de raiz, realizado sobre o suporte cerâmico, apresentou bom acabamento, isento de descontinuidades, com penetração adequada nas laterais do chanfro e reforço de solda apropriado. Em relação à junta soldada, a microestrutura da zona fundida (ZF) obteve predominância de ferrita primária, em suas formas de ferrita de contorno de grão e poligonal, e ferrita com segunda fase alinhada. A microdureza Vickers obteve valores médios abaixo de 180 HV tanto na zona termicamente afetada (ZTA) como na ZF. Os ensaios de dobramento não apresentaram descontinuidades maiores que 3 mm e nos ensaios de tração a ruptura ocorreu no metal base, indicando que o procedimento de soldagem foi adequado. A composição das inclusões tanto do passe de raiz como do ultimo passe de solda possuem os mesmos constituintes, apesar de proporções diferentes, indicando que não houve contaminação do material do suporte cerâmico no cordão de solda.

Modeling of Weld Beads for Laser-GMA Hybrid Welding

For laser-GMA hybrid welds, the relationship between the process parameters and bead shapes was investigated by using the experimental design and the non-linear regression. The weld beads were fitted by two quadratic functions. By the statistical analysis, the primary bead was mainly affected by GMA welding parameters and the root bead was mainly by laser welding parameters. The root bead shaped deeper penetration and shallower width, as the laser power increased for the constant arc power. High laser power resulted in the martensite phase, therefore exhibiting the sudden increase of hardness as approached to the fusion line of the root bead.

Fuzzy control of pulsed GTA welds by using real-time root bead image feedback

Abstract The soundness of steel pipes welds is primarily determined by the quality and penetration of the root pass. In order to ensure quality welds with full penetration, the gas tungsten arc welding (GTAW) process is widely used in industry. Pulsed current GTAW can significantly reduce total welding heat input, weld heat-affected zone (HAZ), residual stresses, and welding distortion, but the welding parameters are more complicated. Usually, the quality of manual GTA welding almost solely depends on the experience of individual welders, but the quality of automatic orbital welding is greatly influenced by proper selection and control of welding parameters to overcome the influences from gravity, arc force, surface tension, heat accumulation, joint preparation, and fit up precision, etc. Consequently, an automatic-welding system without feedback control may easily result in poor welding quality, especially in field welding when the joint preparation and fit up precision are far from ideal. In this paper, an automatic pulsed GTAW system with fuzzy control technique was proposed by using a real-time root bead image feedback, and the width of root pass was used as control indication for full penetration. Bead width of the root pass was determined from CCD images signals using the edge detection technique. The rule of fuzzy controller is based on experiences acquired from welding of single-V grooved plates. Experiments show that the welding quality of steel pipes was very successfully by using this nonlinear, multivariable, on-line controlled pulsed GTAW process.

The microstructure and fracture behavior of the dissimilar alloy 690-SUS 304L joint with various Nb addition

This study investigates the microstructure and fracture behavior of dissimilar weldments of alloy 690 and SUS 304L for various additions of niobium (0.1, 1.03, 2.49, and 3.35 wt pct) in the flux. With identical parameters and procedures, weldments were butt welded by the shielding metal arc welding (SMAW) process using three layers, with each layer being deposited in a single pass. The results indicate that the microstructure of the fusion zone was primarily dendritic and that the contents of Ni, Cr, and Fe within this zone remain relatively constant and resemble alloy 690. With Nb addition, it is noted that the microstructure changes from a cellular to columnar dendrite and equiaxed dendrite. Meanwhile, the dendrite arm spacing reduces and the secondary arms grow longer. Moreover, the composition of the interdendritic phase, whose precipitate volume percentage increases from 5 to 25 pct, changes from Al-Ti-O to Nb rich. The spread of the interdendritic phase is less in the root bead than in the cap bead due to the greater influence of base metal dilution in this region. Mechanical tests indicate that Nb addition increases the average hardness of the weldment and reduces its elongation prior to rupture. However, the tensile strength is essentially unchanged by Nb addition. It is found that the average hardness of the root bead is generally lower than the cap bead, and that the tensile specimens all rupture in the fusion zone, with the fracture surfaces exhibiting ductile features. It is noted that the cap bead tends to rupture interdendritically with increasing Nb addition. Finally, fractography shows that the dimples in the root become larger and shallower with Nb addition and are rich with an interdendritic phase.

Reducing Pipeline Construction Costs: New Technologies

The Oil and Gas industry is constantly looking for ways to reduce capital investment for new projects while maintaining performance and quality standards. As the demand for oil and natural gas increases, so does the need for an expanded network of onshore and offshore transmission pipelines. However, the capital investment associated with new pipelines is enormous. There are a number of materials joining technologies that are being investigated to reduce pipeline construction costs. This document presents three technologies showing particular promise: laser pipeline welding, the use of high strength pipeline materials, and advanced automatic inspection. Test have shown that the HLAW process, which combines the LBW and GMAW processes, is felt to offer a number of benefits in terms of higher potential productivity, ability to produce welds with excellent material properties and a reasonable tolerance for fit-up variations. For existing laser power levels, a viable scenario for implementation of lasers for pipeline welding applications is the use of HLAW for root bead welding, followed by joint filling with conventional mechanised GMAW-P. Concerning the use of high strength pipeline materials, results of a project are presented. The primary objective of this study was to evaluate the mechanical properties of weld metals deposited using a number of commercially available welding consumables and welding processes. This work included characterization of weld metal microstructure, HAC susceptibility of the GMA weld metal and X100 base metal, and solidification cracking of selected welding consumables. The project evaluated commercially available consumables using several welding processes and shielding gases. The third part of the document covers results of a project aiming to collect third-party independent data and statistically characterise the systematic and random errors in girth weld defect sizing, as measured by mechanised ultrasonic testing P/E, TOFD methods and PA ultrasonic technology, in support of pipeline reliability assessments. The defect sizing accuracy of the automated ultrasonic testing (AUT) of girth welds was evaluated using zonal discrimination with focused and non-focused search units arranged for P/E and TOFD methods and PA technology. The objectives were achieved by conducting “open” and “blind” UT trials. NDE flaw verification and destructive testing for flaw size validation were performed. AUT data were collected and statistically analysed.

Effect of chemical composition on root bead surface properties in TIG arc welding.Effect of chemical composition on weldability in fabrication of high‐alloy steel (Report 4)

Effect of chemical composition on root bead surface properties in TIG arc welding.Effect of chemical composition on weldability in fabrication of high‐alloy steel (Report 4)

Experimental study of laser welding with applied electrical potential

The objective of the present study is to develop laser welding with an applied voltage potential, to increase the weld bead root size in laser welding and thereby to improve the welding speed and the butt joint gap tolerance. The influences of the experimental conditions, namely, input laser power, applied voltage between plate and backside electrode, welding speed, plasma operating gaseous species (air, argon, or argon–helium), and the butt joint gap, on the plasma stability and the weld bead were investigated. The weld beads are evaluated from the point of view of the bead appearance, the penetration depth, the ratio of the widths of the weld bead root and weld bead face, and the smoothness of the bead surface. It is found that to stabilise the plasma, it is preferable to set the plate polarity as the cathode (electrode positive), and to use argon or helium gas as a plasma operating gas. Also, it is concluded that this novel method is effective in increasing the bead root/face width ratio, and the melting area. Although it is necessary to optimise the experimental conditions to avoid overheating and melting of the plates, the present method is applicable for higher speed and wider gap butt joint welding than in conventional laser welding.

高合金鋼の溶接施工性に及ぼす化学成分の影響 ４ ＴＩＧ溶接における裏ビード表面性状に及ぼす鋼中化学成分の影響

The effects of chromium and silicon contents on the roughness of root bead surface in gas tungsten inert gas arc welding without inert gas backing was investigated from a point of view of the oxide layer formed on root bead surface. Test welding was carried out on plates containing various contents of chromium and silicon. The roughness of root bead surface was measured by observation of a cross section of weld metal. The thickness of the oxide layer was also measured and chemical compositions were analyzed by EPMA. The roughness of root bead surface increased in weld metals with higher chromium content as a result of the random formation of thick and porous oxide on the root bead surface. The increase of silicon content improved the roughness of root bead surface. The thickness of oxide on root bead surface was thinned by increasing the silicon content and the high silicon concentration was detected at the interface of oxide and the weld metal. From these results, the improvement of roughness of root bead surface by silicon was considered to be due by preventing the random growth of oxide by the formation of a dense silicon oxide layer as a barrier of oxygen diffusion at the interface of oxide and weld metal. The increase of roughness by increasing the chromium content was also considered to be caused by the formation of thick and porous oxide as a result of the prevention of the formation of uniform and dense oxide layer of silicon.

高合金鋼の溶接施工性に及ぼす化学成分の影響 ３ ステンレス鋼のＴＩＧ溶接における溶け込み形状に及ぼすＡ１量の影響

The effect of aluminum content on the penetration behavior in stainless steel tube welded by tungsten inert gas arc welding was investigated from a point of view of the effective oxygen content in molten pool. Girth welding tests were carried out on 18%Cr-9%Ni stainless steel tubes with 0.006-0.030% aluminum and 0.003-0.004% oxygen. The penetration depth, the bead width and the root bead length were measured to evaluate the formability of root bead. Then the aluminum content in weld metal was analyzed. The formability of root bead was deteriorated in proportion to the decrease of penetration depth and the increase of bead width caused by the addition of aluminum to the base metal. The aluminum content in weld metal analyzed was inconsistent with the content estimated from the dilution law but that agree with the content calculated from the solubility of Al2O3. The deterioration of the root bead formability by the increase of aluminum is thought to be caused by the molten metal flow to the molten pool edge induced by the decrease of the soluble oxygen content in molten pool.