Homopolar pulse welding of API 5L carbon steel linepipe

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:115532

Haase, P; Carnes, R; Harville, M ^[1]

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1. Univ. of Texas, Austin, TX (United States)

Homopolar pulse welding (HPW) is a resistance welding process being investigated as a method to rapidly join API 5L carbon steel linepipe. The target application for this investigation is deepwater offshore pipeline construction utilizing the J-lay method, which requires a rapid one-shot welding process for economic feasibility. HPW utilizes the high current, low-voltage pulse produced by a homopolar generator to rapidly resistance heat the interface between abutting workpieces, and follows that pulse with an upset action to produce a weld. A large number of controllable parameters affecting the quality of the resultant weld are present in the process. Three inch nominal diameter, schedule 160 API 5L X-52 pipe sections were welded in this series while controlling variations in generator discharge speed electrode location and upsetting parameters. Welding current voltage and temperature curves were recorded for the welds. Tensile and Charpy V-notch impact specimens were machined from each weld and tested. Weld cross-sections were macroscopically examined. By delaying the application of the forging action, the `white line` or decarburized zone commonly found in high frequency resistance or flash butt welds was eliminated. Weld tensile strength was found to be primarily dependent on generator discharge speed (heat input). Electrode distance from the weld interface was found to be the critical factor determining weld zone cooling rate. HPW parameters can be selected to produce welds without the `white line` or decarburized zone commonly found in high frequency resistance and flash butt welds. Full tensile strength welds are easily achieved providing two conditions are met: sufficient heat input is supplied and a nominal upsetting action is applied within a few seconds of the discharge current peak. Electrode location provides control over the weld zone cooling rate.

• OSTI ID: 115532
• Report Number(s): CONF-9404233--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CARBON STEELS
CHARPY TEST
DECARBURIZATION
ELECTRODES
IMPACT STRENGTH
IMPACT TESTS
PIPE JOINTS
PIPES
RESISTANCE WELDING
TENSILE PROPERTIES
WELDED JOINTS
WELDING RODS