Measuring the process efficiency of controlled gas metal arc welding processes

The thermal or process efficiency in gas metal arc welding (GMAW) is a crucial input to numerical models of the process and requires the use of an accurate welding calorimeter. In this paper, the authors compare a liquid nitrogen calorimeter with an insulated box calorimeter for measuring the process efficiency of Fronius cold metal transfer, Lincoln surface tension transfer and RapidArc, Kemppi FastRoot and standard pulsed GMAW. All of the controlled dip transfer processes had a process efficiency of ∼85% when measured with the liquid nitrogen calorimeter. This value was slightly higher when welding in a groove and slightly lower for the RapidArc and pulsed GMAW. The efficiency measured with the insulated box calorimeter was slightly lower, but it had the advantage of a much smaller random err

Tandem gas metal arc pipeline welding

Energy consumption has grown by 2% per year worldwide over the past ten years. In 2005 worldwide 900,000 barrels of oil and 7.6 billion cubic metre of natural gas were produced daily. The exploitation of fields to meet the increased demands in energy requires the presence of adequate infrastructures. High strength pipeline steels(X100) have been developed to operate at higher pressures allowing a greater volume of fuel to be transported. Additional advantages arising from the reduction in wall thickness contribute to reduction in construction costs and steel volume.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

High-speed GMAW and laser GMAW hybrid welding of steel sheet

Arc welding is the most widely used set of joining technologies in industry today. The automotive tier supplier network and light manufacturing are significant users of arc welding, particularly gas metal arc welding (GMAW) and pulsed GMAW (GMAW-P). For sheet metal welding the majority of welds are single pass fillet welds on T-butt, lap, or edge joints. A fundamental problem and limitation to the use of higher travel speeds in GMAW is the phenomenon of weld bead humping, a weld profile defect with a wavelike profile to the weld bead that has peaks and troughs in the longitudinal direction.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Mechanical characterisation and modelling of resistance welding

Resistance welding is used very extensively in industry for a wide range of applications. Knowledge and measurement of the dynamic characteristics of resistance welding equipment is important in the design of the equipment and in optimization of welding procedures using finite element software. This is especially true for projection welding where accurate measurements of effective lumped mass and damping of the welding head as well as its maximal acceleration and velocity are required for accurate modelling. This thesis describes a new concept where a mechanical model of the welding head is used together with the imposition of a mechanical load step function with simultaneous measurement of resulting head motion to calculate effective lumped mass and damping factor. Two test systems were devised to implement the step function. In the “free fracture test”, a metal or ceramic bar is loaded to its breaking point and resulting welding head velocity is measured. This data allows accurate calculation of machine parameters. The second test uses the explosion of a small metallic element to impose a step function, when the welding current causes the metallic element to explode. The final version of this test “the exploding button test” uses a small cylindrical element fabricated from welding filler wire, with the advantage that both button geometry and material can be controlled. The exploding button test has proved to be very effective, can easily be used for in-situ measurements and avoids the vibrations associated with the free fracture test. These test were applied to evaluate a range of resistance welding machines. Finally, an innovative projection geometry was developed to significantly increase projection weld quality and this design has now been used extensively in industry. The techniques developed in this thesis have been shown to be practical and effective and have enabled much better understanding of machine kinematics. The measurements provide essential data for modelling of projection welding and in guiding the development of resistance welding machines and procedures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Arc-based sensing in narrow groove pipe welding

Big gains in productivity are found in tandem and dual tandem pipeline welding but require highly skilled operators who have to control the position of the torch very accurately for long periods. This leads to high demands on the skills and stamina of the operators of mechanised pipeline welding systems. There is a very strong motivation to fully automate the welding process in order to reduce the required skills and to improve consistency. This project focuses on the use of through-the-arc sensing for seam following and contact-tip-workpiecedistance (CTWD) control. A review of literature reveals very little development work on arc sensing for Pulsed Gas Metal Arc Welding (GMAW-P) in narrow grooves. GMAW-P is often used to achieve optimum properties in weld quality and fusion characteristics and also positional welding capability, all of which are important factors for pipeline welding. The use of through-the-arc sensing for narrow groove pipe welding applications poses specific challenges due to the steep groove sidewalls and the use of short arc lengths, producing very different behaviour compared to V-groove arc sensing techniques. Tandem welding is also quite different from single wire techniques with both wires working in close proximity producing mutual interferences in arc signals. An investigation was conducted in order to assess GMAW-P arc signals and it was found that improved consistency, higher sensitivity and less noise was present in voltages in the peak current period (peak voltages) used for torch position control. As a result of this investigation, a CTWD and cross-seam control system was developed and tested for single and tandem GMAW-P, using a 5º narrow groove. The test results have revealed accuracies for both controls of better than 0.2 mm. CTWD control was developed by following the existent welding procedure voltage average and cross-seam control by peak voltage comparison between maximum torch excursions. Experiments were also performed to evaluate the influence of torch oscillation frequency on arc voltage behaviour and sensitivity, along with weld bead characteristics and fusion profiles. The resultant arc signal sensitivity was consistent with the results found in the literature for conventional GMAW. For GMAW-P, although no data was available from the literature for comparison, the results have shown no increase in sensitivity with the increase of oscillation frequency with the welding setup used. Bead profile analysis performed at different sidewall proximities indicated that optimum wire to sidewall proximities can be found between 0 mm and +0.2 mm, measured from the outer edge of the wire to the sidewall corner. Accurate control is required since +1 mm proximity produced poor sidewall fusion and no signal differentiation for control recognition of groove width. This work showed that negative proximities or wire proximity beyond the sidewall produce wire burn back and hence very long arc lengths, resulting in poor depths of penetration and shallower beads, with major undercut defects. In addition, this work has also shown the importance of torch oscillation width control, in order to produce accurate cross-seam control. A method is proposed to achieve torch oscillation width control by a continuous peak voltage comparison between centre and sidewall torch positions, using the optimum values of wire to sidewall proximity found and the resultant peak voltage value. This control will also provide a clear indication of actual groove width. Clearly this data can also be used to implement a system which adapts welding parameters to groove width.EThOS - Electronic Theses Online ServiceBP Exploration and Pipeline Research Council International (PRCI)GBUnited Kingdo

Advances in gas metal arc welding and application to corrosion resistant alloy pipes

According to recent estimations, the construction of pipelines will continue to increase during the next thirty years, in particular as a result of oil and gas discoveries in remote locations. Significant advances in welding technology during the last ten years have potential to provide improvements in productivity, quality and structural integrity of pipe girth welds. In this thesis, several new processes Lincoln STT, Lincoln RapidArc, Fronius CMT, Fronius CMT-P and Kemppi FastROOT have been compared the first time to the GMAW-P to understand how these new waveforms operate for pipe welding. The process setting parameters have been analysed to understand their effect on metal transfer and arc stability control, and on bead shape characteristics. Although all waveforms present similar burn-off ratios, individual waveforms differ considerably, and especially the arc voltage waveform. This leads to considerable differences in the mechanism of metal transfer and the stability of the processes under similar experimental conditions. Understanding of these new waveforms in terms of the effect of setting parameters in the mechanism of metal transfer, process stability and melting phenomena provides a basis for assessing the potential of these processes for a range of applications, and in particular application to CRA pipe root welding Since the arc energy is the overall energy delivered from the power source at the contact tip of the torch, and part of that energy is not absorbed by the workpiece, research was performed to measure the process efficiency associated with some of these waveforms and process setting conditions. The study led to a better understanding of the potential errors in calculating process efficiency. The results obtained show that all the short-circuiting waveforms analysed (i.e. CMT, STT and FastRoot) had a similar process efficiency of 90±3%, while pulse spray waveforms (GMAW-P, CMT-P and RapidArc) are characterized by lower process efficiency, approximately 78±3%. The application of these waveforms to the welding a narrow groove pipe with a “J” groove design was investigated. These analyses were focused on the variation of bead shape characteristics and welding quality performance based on the analysis of the conditions that result in lack of penetration and top bead defects, such as lack of side wall fusion or undercutting. It was observed that RapidArc and CMT-P are able to satisfy the quality requirements, i.e. full penetration and absence of defects for the specific conditions described in this thesis. High welding speeds (up to 1m/min) were achieved with these processes, four times the typical speed 0.25m/min. Finally, the shielding gas plays an important role in terms of quality and weld bead performance. This led to an optimization of the shielding gas composition used, based on mixtures of carbon dioxide, argon and helium. Statistical modelling was undertaken to optimize the shielding gas mixtures using RapidArc and CMT-P waveforms. In parallel, a new purging shielding gas device was designed to achieve a weld root free of oxidation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Pavement Management Roadmap

693JJ319D000018693JJ320F000206The FHWA\u2019s update to its Pavement Management Roadmap helps to identify the steps that will address current gaps in pavement management and to establish research initiatives and priorities. Initial gaps were identified based on a literature review, project team knowledge, and a satisfaction survey of Federal, State, and local pavement management practitioners (authorized under Office of Management and Budget control number 2125-0628). They were grouped according to four themes: Theme 1 \u2013 Data, Theme 2 \u2013 Pavement Management Analysis Tools and Other Applications, Theme 3 \u2013 Workforce and Organization Issues, and Theme 4 - Technological Advancements \u2013 New Tools, Methodologies, and Technology. The Roadmap was derived from a series of virtual stakeholder workshops in which representatives from State and local agencies, academia, private industry, and the FHWA met to discuss and prioritize suggestions for enhancing current practices. The Roadmap contains 72 action items (46 short-term and 26 long-term) in 15 improvement areas across the four themes. The results can be used to determine new research, development, and technology transfer opportunities

Regulation of pH by Carbonic Anhydrase 9 Mediates Survival of Pancreatic Cancer Cells With Activated KRAS in Response to Hypoxia.

Background & Aims Most pancreatic ductal adenocarcinomas (PDACs) express an activated form of KRAS, become hypoxic and dysplastic, and are refractory to chemo and radiation therapies. To survive in the hypoxic environment, PDAC cells upregulate enzymes and transporters involved in pH regulation, including the extracellular facing carbonic anhydrase 9 (CA9). We evaluated the effect of blocking CA9, in combination with administration of gemcitabine, in mouse models of pancreatic cancer. Methods We knocked down expression of KRAS in human (PK-8 and PK-1) PDAC cells with small hairpin RNAs. Human and mouse (KrasG12D/Pdx1-Cre/Tp53/RosaYFP) PDAC cells were incubated with inhibitors of MEK (trametinib) or extracellular signal-regulated kinase (ERK), and some cells were cultured under hypoxic conditions. We measured levels and stability of the hypoxia-inducible factor 1 subunit alpha (HIF1A), endothelial PAS domain 1 protein (EPAS1, also called HIF2A), CA9, solute carrier family 16 member 4 (SLC16A4, also called MCT4), and SLC2A1 (also called GLUT1) by immunoblot analyses. We analyzed intracellular pH (pHi) and extracellular metabolic flux. We knocked down expression of CA9 in PDAC cells, or inhibited CA9 with SLC-0111, incubated them with gemcitabine, and assessed pHi, metabolic flux, and cytotoxicity under normoxic and hypoxic conditions. Cells were also injected into either immune-compromised or immune-competent mice and growth of xenograft tumors was assessed. Tumor fragments derived from patients with PDAC were surgically ligated to the pancreas of mice and the growth of tumors was assessed. We performed tissue microarray analyses of 205 human PDAC samples to measure levels of CA9 and associated expression of genes that regulate hypoxia with outcomes of patients using the Cancer Genome Atlas database. Results Under hypoxic conditions, PDAC cells had increased levels of HIF1A and HIF2A, upregulated expression of CA9, and activated glycolysis. Knockdown of KRAS in PDAC cells, or incubation with trametinib, reduced the posttranscriptional stabilization of HIF1A and HIF2A, upregulation of CA9, pHi, and glycolysis in response to hypoxia. CA9 was expressed by 66% of PDAC samples analyzed; high expression of genes associated with metabolic adaptation to hypoxia, including CA9, correlated with significantly reduced survival times of patients. Knockdown or pharmacologic inhibition of CA9 in PDAC cells significantly reduced pHi in cells under hypoxic conditions, decreased gemcitabine-induced glycolysis, and increased their sensitivity to gemcitabine. PDAC cells with knockdown of CA9 formed smaller xenograft tumors in mice, and injection of gemcitabine inhibited tumor growth and significantly increased survival times of mice. In mice with xenograft tumors grown from human PDAC cells, oral administration of SLC-0111 and injection of gemcitabine increased intratumor acidosis and increased cell death. These tumors, and tumors grown from PDAC patient-derived tumor fragments, grew more slowly than xenograft tumors in mice given control agents, resulting in longer survival times. In KrasG12D/Pdx1-Cre/Tp53/RosaYFP genetically modified mice, oral administration of SLC-0111 and injection of gemcitabine reduced numbers of B cells in tumors. Conclusions In response to hypoxia, PDAC cells that express activated KRAS increase expression of CA9, via stabilization of HIF1A and HIF2A, to regulate pH and glycolysis. Disruption of this pathway slows growth of PDAC xenograft tumors in mice and might be developed for treatment of pancreatic cancer