Per Thomas Moe

Hot Metal Extrusion

The paper focuses on the main scientific problems related to hot metal extrusion of thin walled tube, strip and sections, covering analytical approach, 2D- and 3D-numerical simulation and experimental validation. The main physical phenomena and parameter estimation related to thermo-mechanical constitutive equations, shear localization, bearing channel, dry hot friction and metal flow stability in extrusion is treated. The scientific, generic insight and knowledge of these extrusion phenomena should be considered as precompetitive. In industry this knowledge must be integrated with practical experiences and skills in order to be able to predict and control dimensional, surface and microstructure variability during a press cycle, and inspire to innovations in the field of extrusion and its down stream processes such as tube drawing, cold forging, bending and hydroforming.

Optical Measurement Technology For Aluminium Extrusions

Optical measurement techniques such as laser scanning, structured light scanning and photogrammetry can be used for accurate shape control for aluminum extrusion and downstream processes. The paper presents the fundamentals of optical shape measurement. Furthermore, it focuses on how full‐field in‐ and off‐line shape measurement during pure‐bending of aluminum extrusions has been performed with stripe projection (structured light) using white light. Full field shape measurement is difficult to implement industrially, but is very useful as a laboratory tool. For example, it has been clearly shown how moderate internal air pressure (less than 5 bars) can significantly reduce undesirable cross‐sectional shape distortions during pure bending, and how buckling of the compressive flange occurs at an early stage. Finally, a stretch‐bending set‐up with adaptive shape control using internal gas pressure and optical techniques is presented.

Analysis and Design of Small Scale Pipe Forge Welding Process

Shielded Active Gas Forge Welding is a high speed welding method for joining inter alia steel pipeline and casing. The process consists of a heating step, in which the bevels of the sections to be joined are heated locally to temperatures exceeding 1000 °C, and a subsequent forging step in which joining takes place by the application of a high axial force. In order to make possible cost-effective welding qualification and research a small scale forge welding machine has been developed. Down-scaling of the forge welding process should be carefully assessed in order to establish the limits of the process. In this paper two aspects of the forge welding process have been studied in detail by the use of finite element modeling and experiments: a) coupled thermal and electromagnetic modeling of heating and b) coupled thermo-mechanical modeling of forging. Special attention is given to the study of the limits of buckling of the pipe wall during forging. A high thermal gradient in the axial direction in the pipe wall facilitates local plastic deformation during forging and proper fusion of welds. For elongated temperature fields buckling is more likely to occur since the effective stiffness of the wall section is reduced. The limits of buckling depend on the wall thickness and diameter of section to be joined. While the forge welding process works very well for virtually all types of full scale pipeline and casing sections, buckling has been observed when joining very thin-walled small scale pipes. For welding of stainless steel small scale pipes local heating proves challenging. These challenges may be overcome by innovative welding machine design, and by carefully assessing welding process limitations. Certain physical limitations must still be considered.Copyright

Microstructure and Mechanical Properties of API 5CT L80 Casing Grade Steel Quenched From Different Temperatures

The continuous development of line pipe and casing grade steels should be complemented by development of more effective welding methods. A special high temperature high speed forge welding technique called Shielded Active Gas Forge Welding (SAG-FW) has been developed to weld steel pipes for a range of applications. This article focuses on the microstructure development at different welding conditions in L80 steel with 0.25%C. Specimens with dimensions 100 mm × 11 mm × 6 mm were extracted from the wall of a large diameter L80 pipe. A SMITWELD thermal simulator was used to simulate heat treatment conditions using electrical resistance heating. The specimens were heated to peak temperatures ranging from 600°C to 1350°C within 10 s and subsequently quenched to 50°C at a constant rate of 60°C/s to simulate the heat-affected zone conditions for the real SAG-FW process. Martensite with small fractions of bainite was observed for higher peak temperatures. Mixed microstructures were observed in the specimens heated in the intercritical temperature range. Microstructures and phase fractions developed after heating to different peak temperatures have been analyzed by optical microscopy and scanning electron microscopy. Charpy V-notch tests and Vickers microhardness measurements have been carried out for the weld simulated specimens. The observed toughness values, hardness values, microstructures and phase fractions have been correlated to the respective weld simulation parameters.Copyright

Mechanical Integrity Modeling of Forge Welded Pipes for Offshore Applications

In this paper, we discuss how through-process multi-scale models can be designed and combined with properly constructed experiments in order to assess the mechanical integrity of forge welded connectors. Shielded Active Gas Forge Welding (SAG-FW) is a fully automatic solid state method for joining steel pipes and other metallic articles. After heating, welding occurs almost instantaneously when the mating surfaces of the metallic parts are brought into intimate contact at high temperature and co-deformed. The result is a metallic bond with properties similar to those of the base material. If mating surfaces have been properly prepared and are essentially free from oxides the forge weld line is completely indistinguishable even when studied under a microscope. However, improper surface finish, oxides and contaminants may contribute to reducing weld quality. The paper consists of analytical and experimental parts. First, approaches for modeling forge welding and weld integrity are assessed. Second, a Gurson-type model is studied in great detail as it appears to be the simplest and most promising concept in relation to quantitative modeling and testing of mechanical integrity of forge welds. Third, miniature notched specimens for determining parameters of a modified Gurson-model are proposed and evaluated in relation to small scale forge welding. The small scale forge welding method has been established in order to simulate full scale welding of for example line pipe and casing, but mechanical testing of small samples constitute a significant challenge. Fourth, a set of experiments is performed to further assess the concept, to the extent possible determine material parameters of the Gurson-model and to evaluate the effect of process parameter settings on the weld quality. Results from tests of welds with and without oxides are subsequently compared with results from tests of base material specimens. All tests have been performed for an API 5L X65 alloy. The results demonstrate that both capacity and ductility of the forge welds are similar to those of base material. Finally, Gurson-model parameters are assessed, and a comparison with physical observations is made. Further development of the small scale tests is needed. More extensive test programs should be performed and a comparison with full scale welding should be carried out. However, the experiments demonstrated that the proposed notched specimen designs complements conventional fracture mechanical tests (CT, SENT, SENB) or field tests proposed by various standards (Charpy, Izod, bend tests).Copyright

Establishment of Testing Methodology for Forge Welded Tubular Products

A state-of-the-art small-scale solid state forge welding machine has been fabricated for checking weldability by Shielded Active Gas Forge Welding (SAG-FW) of tubular products applicable predominantly for, but not limited to offshore Industries. Effective, fast and inexpensive welding and testing of joints make this small-scale method suitable for evaluating weldability of a material before starting regular qualification and fabrication in a full-scale welding machine normally located in spool base or offshore. The small-scale machine provides a complete package for pre-qualification studies, including assessment of welding conditions, material flow behavior, heat treatment options. However, there are considerable challenges relating to application of international standards of testing as well as interpretation and use of results in the context of large-scale welding. In this paper results from small-scale welding and weld characterization of an API 5L X65 quality are presented. First, a detailed test plan for analyzing the weld is outlined. This procedure is subsequently applied for checking the welds to be produced in the full-scale machine. Short-comings in using the small-scale process as well as the possible remedies are discussed in detail.Copyright

Studies on Shielded Active Gas Forge Welded API 5CT L80 Material at Different Cooling Rates

Shielded Active Gas Forge Welding (SAG-FW) is a solid state bonding process in which two mating surfaces are locally heated and forged together to form a bond. SAG-FW has so far mainly been used to join materials for pipe-line and casing applications. The present study has been conducted on an API 5CT L80 grade material in a prototype forge welding machine. Small-scale pipe specimens have been extracted from the wall of the production casing. The SAG-FW process is completed within a few seconds of heating and forging followed by controlled cooling. The microstructure of the weld is determined by the processing parameters. In this paper, microstructure results for SAG-FW processed L80 material have been obtained for a range of cooling rates and systematically compared with microhardness values. Microstructure observations at different regions of the weld have been made. Faster heating rate and controlled cooling resulted in a mixture of non equilibrium microstructures, but satisfactory mechanical properties have been obtained for optimized processing parameters.

Welding Procedure Establishment for Tubular Joints Welded by Single Station, Solid State Welding Machine

Forge welding is an efficient welding method for tubular joints applicable in oil and gas industries due to its simplicity in carrying out the welding, absence of molten metal and filler metals, small heat-affected zone and high process flexibility. Prior to forging, the ends (bevels) of the joining tubes can be heated by torch or electromagnetic (EM) techniques, such as induction or high frequency resistance heating. The hot bevels are subsequently pressed together to establish the weld. The entire welding process can be completed within seconds and consistently produces superior quality joints of very high strength and adequate ductility. Industrial forge welding of tubes in the field is relatively expensive compared to laboratory testing. Moreover, at the initial stages of a new project sufficient quantities of pipe material may not be available for weldability testing. For these and several other reasons we have developed a highly efficient single station, solid state welding machine that carefully replicates the thermomechanical conditions of full-scale Shielded Active Gas Forge Welding Machines (SAG-FWM) for pipeline and casing applications. This representative laboratory machine can be used to weld tubular goods, perform material characterization and/or simulate welding and heat treatment procedures. The bevel shapes at mating ends of the tubes are optimized by ABAQUS® simulations to fine tune temperature distribution. The main aim of this paper is to establish a welding procedure for welding the tubular joints by the representative laboratory machine. The quality of the welded tubular joint was analyzed by macro/micro analyses, as well as hardness and bend tests. The challenges in optimizing the bevel shape and process parameters to weld high quality tubular joints are thoroughly discussed. Finally a welding procedure specification was established to weld the tubular joints in the representative laboratory machine.Copyright

Aluminum Rod Extrusion and Material Modeling

The article presents an outline of a scientific approach for testing constitutive relations for the aluminum extrusion process. By comparing ram force, container friction, die face pressure, outlet temperature measurement during rod extrusion with corresponding simulated data, inferences can in principle be drawn with respect to the validity models. The paper indicates that simulation results from the 2D ALMA2π program are in fair agreement with measurements during extrusion of AA6060, but more work needs to be done to control thermal conditions during extrusion.