Pipeline operations are a varietal complex of underground arteries, terminals, compressor and pumping stations, all of which help to transport natural gas, crude oil, refined products, water, coal and many other commodities from producing areas to marketing areas. Major oil and gas pipelines crisscross continental United States with a total of over 750,000 miles of steel tubes that represent capital expenditures of billions of dollars and a source of work for thousands of skilled craftsmen.Since the oil and gas industries represent a major segment of the pipeline users, this discussion will center about such pipelines.Pipeline welding is one of the major fields of endeavor in the welding industry and, conversely, welding is the outstanding factor in making modern pipelines economically possible.The economy of pipeline construction and operation demands that new developments in welding methods be applied to this work as soon as they can be adapted to the rigorous requirements of cross country operations.