Metallurgische Grundlagen als Basis zur Entwicklung alternativer Schweißzusatzwerkstoffe im Pipelinebau

Translated title of the contribution: Metallurgical basics as a fundamental for the development of alternative welding consumables in the pipeline industry

Michael Stephan Fiedler

Research output: ThesisDoctoral Thesis

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Abstract

Nowadays the welding of pipeline girth welds are predominantly made with the shielded metal arc welding process (SMAW) as well as the gas metal arc welding process (GMAW) by using solid and flux cored wires. An alternative welding process by utilization of self shielding flux cored wires (FCW) may theoretically combine the advantages of stick electrodes with semiautomatic processes like the GMAW process but is a big challenge for the development engineer of such products. This work describes the metallurgical basics as a fundamental for the development of self shielding flux cored wires, which leads finally in a successful established product in the pipeline industry. The nature of self shielding FCW is that the product needs no auxiliary shielding gas. Due to this fact the filling of the wire have to take over the entire task of the shielding gas - primary to prevent absorption of detrimental acting elements as nitrogen, oxygen and hydrogen from the ambient air. This task may roughly divide into two modes of operation the displacing of air by gas- and vapour- formers and secondly the bonding of nitrogen with special elements. The displacement of air is ensured by dissociating and evaporating components like carbonates, fluorides, as well as metals, added to the flux, whereby the resulting interactions with the drop transition is a main cognition of this work. An indication for the alternating formed shielding atmosphere offers the maximum drop diameter, which was initially investigated and finally optimized by prototypes with varying filling concepts. The necessary investigation in this field is the evaluation of raw materials regarding the dissociation and evaporation behaviour. To evaluate the behaviour of raw materials the parameters for the measurement have to be adapted to correlate more or less with welding processes. A stepwise development including different vapour and CO2- formers in fluxes improves the shielding effect, recognizable by lower nitrogen content. Two optimized prototypes with different filling systems are finally evaluated regarding the produced vapour, furthermore the vapour is analysed and compared with theoretical considerations. Nevertheless a certain air access is possible and nitrogen is picked up during welding. Due to several optimization steps of filling powders the nitrogen content may significantly reduced to values of approximately 250ppm. Via thermodynamic simulation of different denitration combinations the precipitation behaviour became investigated and evaluated per microscopic evaluation.
Translated title of the contributionMetallurgical basics as a fundamental for the development of alternative welding consumables in the pipeline industry
Original languageGerman
QualificationDr.mont.
Supervisors/Advisors
  • Krieger, Wilfried, Supervisor (internal)
Publication statusPublished - 2008

Bibliographical note

embargoed until null

Keywords

  • Welding Pipeline laying self shielded flux cored wires binding of nitrogen protection of weld metal from the ambient air

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