Homopolar Pulsed Welding for Offshore Applications

As a low impedance energy-storage device, the pulsed homopolar generator (RPG) is capable cif delivering a multimegawatt, megampere-current pulse into a resistive or inductive load with high efficiency. Such HPGs have been used for over ten years as power supplies for research in high energy, high-rate processing of metal alloy components and systems. Most of these processes rely on resistive heating during the current pulse to rapidly heat the material as required for a particular process. One such application is homopolar pulsed welding (HPW), a solid state, forged welding process in which heat generation is concentrated at the interface between workpieces as homopolar current is conducted between them. Because of the very high peak current and power (from 8 to 20 kNcm2 and 50 to 100 kW/cm2), weld time is very short, reducing time-at-temperature exposure and related microstructural changes. Welding is accomplished in air, no flux or filler is used, and the interface disappears completely in a good weld. This paper reports on recent and ongoing research into the weldability by HPW of various alloys applicable to offshore systems, including stainless steel and titanium alloys, but primarily focusing on carbon-steel pipe. This research includes an investigation of weld parameters, sensitivity of the process to the weld parameters, metallurgical and mechanical evaluation of weld quality, and the development of a real-time quality assurance capability that can certify nondestructively an HPW weld before it is removed from the welding fixture. The research presented here is sponsored by the National Science Foundation (NSF) and various private industry companies.Center for Electromechanic

Homopolar Pulsed Welding of Steel Pipe: Effects of Controlled Parameters on Weld Properties

This paper reports on recent and continuing research into the optimization of the homopolar pulsed weld (HPW) process for welding 89-mm diameter, ASTM 1035 steel pipe. Present study characterizes the typical macro- and microstructure found in HPW and seeks to identify causes of low toughness. Metallurgical and mechanical evaluation indicated nonuniform heating around the circumference of the pipe. New electrodes were fabricated and shown to reduce circumferential nonuniformity in the weld specimens, and improve the weld repeatability. Several experiments were performed that varied process control parameters, one at a time, and identified the effects on weld properties. However, the process control parameters investigated did not improve the weld toughness. The reduced toughness at the weld line of the HPW process is attributed to the large grain size present on this region.Center for Electromechanic

Homopolar Pulsed Welding for Offshore Applications

Center for Electromechanic

Homopolar Pulsed Welding: Interface Properties of High Strength Steel Pipe, a Technical Note

This note discusses the microstructure, hardness, and toughness of a homopolar weld (HPW) performed on API 5L grade X-52 line pipe (90 mm diameter and 10 mm wall thickness). Homopolar welding is a solid state welding process made possible by a large pulse of direct current from a homopolar generator (HPG) The heat generated by electrical resistance leads to complex phase transformations resulting in different structures with different characteristics. The results show the weld properties are affected by the pipe materials and that HPW is a promising process for joining high strength steel pipe.Center for Electromechanic

Homopolar Pulse Welding: Characterization of Weld Parameters

This paper reports on the continuing research in homopolar pulse welding (HPW) as applied to pipe welding. As part of the NSF/Offshore Technology Research Center (OTRC). The program is designed to develop and commercialize this relatively new technology. The goal is to fully characterize the relative importance of the many coupled process variables and develop a real-time quality assurance system that will nondestructively determine the quality of a weld by simple electrical measurements. Potential commercial applications of HPW include large diameter pipe and other structures where a large cross-section must be welded quickly (i.e. laying of pipe with deep-sea lay barges, and construction of tension legs in the new deep-water tension leg drilling platforms) (Chung, 1985).Center for Electromechanic

Homopolar Pulsed Welding of API Line Pipe

Homopolar pulse welding is a welding process that is being developed to rapidly join API line pipe. This process has particular potential for application in offshore pipeline construction utilizing the J lay method. The weld joint produced has high strength and a narrow heat affected zone. There is a thin brittle zone at the weld interface, resulting in low impact toughness. The weld line is characterized by a very thin >light band>, believed to be a ferrite rich zone produced by a combination of localized melting and mechanical upset. Current developmental research is progressing to eliminate this brittle zone and improve weld geometryCenter for Electromechanic

Newton Algorithms for Analytic Rotation: an Implicit Function Approach

component loss criterion, factor analysis, gradient projection algorithm, oblique rotation, orthogonal rotation, orthogonal matrix, planar algorithm, principal components,

Influência da interação touro x rebanho na estimação da correlação entre efeitos genéticos direto e materno em bovinos da raça Nelore Influence of sire x herd interaction on the estimation of correlation between direct and maternal genetic effects in Nellore cattle

A interação touro x rebanho foi avaliada em uma população com 30.789 registros de animais da raça Nelore nascidos entre 1984 e 1994 em doze fazendas localizadas em três Estados do Sudeste e Centro-Oeste brasileiro, com um total de 48.495 animais no pedigree. As características consideradas foram os pesos ao nascer (PESNAS) e à desmama (PESDES) e o ganho de peso da desmama ao sobreano (GP345). O efeito da interação touro x rebanho foi considerado aleatório em modelos animais uni e bicaraterística, usando MTDFREML. Esse efeito foi importante para PESNAS (6% da variância fenotípica) e influenciou os componentes de variância e covariância e, conseqüentemente, os parâmetros genéticos. O efeito foi menor (cerca de 1% da variância fenotípica) para PESDES, mas alterou as estimativas dos componentes de variância e covariância. Para GP345, o efeito foi pequeno, embora significativo pelos verossimilhança. As correlações genéticas entre efeitos direto e materno são próximas de zero, ou até mesmo positivas, se a interação touro x rebanho for incluída no modelo, e sempre negativas se ela for omitida.<br>Sire x herd interactions were studied in 30,789 records of birth (BW) and weaning weight (WW) and weight gain from weaning to 18 months of age (G345) of Nellore cattle born from 1984 to 1994 in twelve farms located in three states of central and southeastern Brazil, with a total of 48.495 animals in pedigree. Sire x herd interaction was considered as a random effect in single trait and two traits animal models using MTDFREML. This effect was important for BW (6% of the phenotypic variance) and it both affected variance and covariance components and, consequently, genetic parameters. The effect was smaller for WW (around 1% of the phenotypic variance), but influenced the estimates of (co) variance components. For G345, Sire x Herd effect was small. Likelihood tests showed that this effect was significant for all traits. This study showed that genetic correlations between direct x maternal effects are close to zero or even positive if sire x herd interaction is fitted in the model, and always negative if it is not

A Multivariate Multilevel Approach to the Modeling of Accuracy and Speed of Test Takers

speed, accuracy, IRT, response times,