Evaluation of Welding Techniques for Stainless Steels Piping Without Use of Backing Gas

Abstract

In the piping fabrication industry Gas Tungsten Arc Welding (GTAW) is used extensively for welding of stainless and high alloy steel pipes, mainly for root pass of single side joints. GTAW process uses an inert gas for both shielding and backing of the weld. Backing gas also known as purge gas, is provided mainly to prevent oxidation of root pass weld from inside the pipe. Typically, Argon or Argon mixture (i.e. Argon with Helium, etc.) are used as backing gas. Argon gas, is colorless, odorless and heavier than air. Many safety incidents have occurred in the Oil and Gas industry (mainly during construction phase) due to asphyxiation. This has typically occurred when a person (usually a welder) goes inside the piping (a confined space) to inspect the root pass weld to ensure it will pass radiography test. Construction industry has failed to fully tackle this issue in a meaningful way and as a result, some significant number of fatalities occur each year. On several occasions, such incidents have resulted in multiple fatalities when coworkers enter the confined space to rescue and become a victim by themselves. There are a multitude of reasons why people put themselves at risk in this way. Reasons given for a reluctance to use alternative techniques that eliminates backing gas are many and varied. Alternate welding techniques without backing gas were developed many years ago. However, they are still not being used extensively for many reasons and apprehensions. Using these alternate welding techniques with right controls in place, can eliminate the hazard associated with backing gas and improve safety and maintain quality. This paper discusses and evaluates the alternate welding techniques (which do not require backing gas), limitations, welding procedure qualification and inspection requirements.