Homopolar Pulse Welding for Offshore Deep Water Pipelines

Abstract

Homopolar Pulse Welding (HPW) is a one-shot resistance welding process being investigated as a method to join API 5L carbon steel line pipe. HPW utilizes the high current, low voltage electrical pulse produced by a homopolar generator to rapidly resistance heat the interface between abutting pipe ends, producing a full circumference resistance forge weld requiring no filler metal in under three seconds. A five year joint industry program is sponsoring HPW research with the goal of developing the process for deep water offshore pipeline construction utilizing the J-lay method. The first two years of the program have concentrated on weld parameter optimization by producing, testing, and evaluating welds in various grades, wall thicknesses, types and compositions of 3 inch nominal (3.5 inch OD) diameter API 5L carbon steel pipe. Mechanical properties of the welds and parent metal were evaluated by tensile testing, impact testing, and hardness traverse testing according to guidelines and criteria established by the industrial sponsors. HPW has demonstrated the capability to produce industrially acceptable full circumference welds in carbon steel pipe via a rapid, one-shot process.