Welding Consumables, Characterizations and Usages of Metal Arc Welding - Under Oil (MAW-UO)

Several welding repair methods are currently available for cross-country pipelines, tanks and vessels; examples of these are hot-tapping and sleeve-repairs that repair the pipeline externally while in-service. Other repair methods would require the service to shutdown. Metal arc welding under oil (MAW-UO) is a new process that was invented and developed at the Colorado School of Mines (CSM) to make in-situ internal repairs on oil pipelines. Welding to correct flaws and corrosion damages would be performed in-service and without the need to evacuate the service from the containing fluid. This method offers the oil industry an alternate welding repair technique that is more flexible than the existing methods.

MAW-UO process provides pipeline repairs on the difficult or impossible to reach places such as buried, under bodies of water, under highways, or under congested intersections segments. To prove the concept of metal arc welding - under oil (MAW-UO), two sets of consumables were selected for experimentation:  1) steel welding wires and 2) high nickel alloy welding wires. Commercial steel wire paired with MAW-UO demonstrated great potential for pipeline repairs. The high nickel alloy welding wires, however, controlled the phase transformations of the solidifying weld metal to produce a tough, relatively soft, austenitic weld metal.

The MAW-UO process using the high nickel alloy welding wire at this time is the only  method for in-situ repairs of flaws and corrosion damages on the inside surfaces of a cross-country pipeline, tank or vessel by welding. The use of MAW-UO with nickel alloy welding wires for in-situ internal repairs is expected to meet the rising demands of the oil industry involving mechanical or corrosion damage without the need of shutting-down these services.