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Homopolar Pulse Butt Welding of API 5L Line Pipe

by Paul W. Haase, Univ of Texas at Austin, Austin, United States,
Zwy Eliezer, Univ of Texas at Austin, Austin, United States,
Robert Carnes, Univ of Texas at Austin, Austin, United States,
John Gully, Univ of Texas at Austin, Austin, United States,
Mike Harville, Univ of Texas at Austin, Austin, United States,



Document Type: Proceeding Paper

Part of: Civil Engineering in the Oceans V

Abstract:

Homopolar pulse welding (HPW) is a welding process that is being investigated as a means to rapidly join API line pipe, having particularly great potential for application in deepwater offshore pipeline construction using the J-lay method. Homopolar pulse welding utilizes the high current, low voltage pulse produced by a homopolar generator to rapidly resistance heat the interface between two metal components to forging temperature, at which time an upset force is applied to produce a forge weld at the interface, requiring only a few seconds from initiation of the pulse to completion of the weld. Currently, welds can be produced having high strength and a narrow heat affected zone (HAZ), but also possessing a thin brittle zone at the weld interface, resulting in low impact toughness. Developmental research into homopolar pulse butt welding of API 5L X52 carbon steel line pipe is being pursued to eliminate this brittle zone. A large number of parameters (including initial contact pressure, initial surface preparation, current pulse magnitude and shape, amount of upset and upset timing) affect the quality, microstructure and mechanical properties of the weld and heat affected zone. The results of research to characterize the influence of processing parameter variations on microstructure and mechanical properties is presented.

Subject Headings: Welding | Steel pipes | Steel structures | Offshore pipelines | Underwater structures | Underwater pipelines | Microstructure

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