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Date: February 1999
For more than 20 years, electroslag welding has been banned from use on primary structural tension members (such as heavy flanges and cover plates) on bridges built with Federal-aid highway funds. The moratorium issued by the Federal Highway Administration (FHWA) in 1977 was prompted by the discovery of a large crack in an electroslag weld on an Interstate highway bridge near Pittsburgh. The moratorium effectively eliminated the use of electroslag welding on all U.S. bridges. Conventional processes, like submerged arc welding and shielded metal arc welding, have been used instead.
The ban is expected to be lifted soon, however, as a result of an FHWA-sponsored comprehensive research project to determine the cause of the welding problems. That project led to a significantly improved electroslag welding technique, known as narrow-gap improved electroslag welding, or NGI-ESW.
Electroslag welding is a process used to join thick steel plates in a vertical position. A consumable guide bar is placed between the plates. This bar guides an electrode wire. The plates are joined together by melting the plate edges, the guide bar, and the electrode wire in a pool of molten metal shielded by a flux bath (slag). The flux is kept molten due to electrical resistance to the current passing through the slag.
With NGI-ESW, the magnitude of electric current applied is much greater than in conventional electroslag welding, and the gap between the plates, and hence the amount of molten material used, is relatively small. This results in a higher welding speed.
"The new process increases the toughness and reliability of the weld, increases productivity in the welding process, and decreases the amount of heat input required," says Bill Wood of the Oregon Graduate Institute of Science and Technology (OGIST).
In the 1980s, FHWA asked OGIST to research and develop an improved electroslag welding process. The result-NGI-ESW-is faster and consumes less energy than conventional electroslag welding, and it produces a consistently tougher weld, according to FHWA's Krishna Verma, who is managing the research project. In 1993, FHWA issued a 4-year contract to the Basic Industrial Research Laboratory (BIRL) at Northwestern University in Evanston, Illinois, to conduct demonstrations of the NGI-ESW technique and to verify its weld quality, including toughness. BIRL developed a comprehensive package of technical specifications and training guides for State transportation agencies and bridge fabricators, to assist them in applying the new electroslag technology. It did not, however, conduct any demonstrations. Later, this package was updated at OGIST under a new contract, which also required that 2 pilot presentations and 18 additional demonstrations be conducted throughout the country.
To demonstrate the new process to State bridge and highway engineers and the steel fabrication industry, FHWA, as part of Demonstration Project 102, is sponsoring a series of hands-on workshops around the country over the next 18 months.
According to Milo Cress of FHWA's Nebraska Division, "We want to get as many people as possible to participate in the NGI-ESW demonstrations. Every fabrication shop and every State materials shop should see how it works."
A workshop sponsored by the National Bridge Research Organization (NABRO) was held in December at the University of Nebraska at Lincoln. Atorod Azizinamini of NABRO, who participated in the workshop, said, "As a researcher in the field of bridge engineering, I was very impressed, and the research results seem to support requesting FHWA to lift the moratorium on electroslag welding in bridges."
The Nebraska Department of Roads' Ron Liston, who was also on hand for the workshop demonstration, agrees. "We have confidence that this will be a good process," says Liston. "The narrow gap part has made this process acceptable, and I sense there are steel fabricators ready to try it."
Some bridge engineers never lost confidence in electroslag welding, despite the moratorium. "There are many bridges with electroslag welded members and none have failed," says Wood. "These bridges have been standing for 30 or 40 years. If you consider the stability of existing in-service electroslag weldments and add the greatly improved toughness and reliability that we have now, you have a welding process and procedure ready to be used."
The new NGI-ESW process will have applications far broader than highways. "This new process creates tremendous opportunities not only for highway bridges, but also for the railroad industry, the building trades, offshore oil platforms, and heavy equipment construction, " says Bob Turpin of OGIST.
For more information about the NGI-ESW process or the demonstration schedule, or if you are interested in hosting a demonstration, contact Krishna Verma at FHWA (telephone: 202-366-4601; fax: 202-366-3077; email: firstname.lastname@example.org). Information can also be found on the Web at www.fhwa.dot.gov/bridge/.
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