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|Federal Highway Administration > Publications > Public Roads > Vol. 59· No. 3 > Narrow-Gap Improved Electroslag Welding for Bridges|
Narrow-Gap Improved Electroslag Welding for Bridges
by Krishna K. Verma
A new FHWA program is helping engineers and fabricators learn about this new advanced welding technology.
Electroslag welding (ESW) is a process that joins metals with heat generated by the passage of electric current through molten conductive flux, melting the filler and base metals. Now in its final stage, a comprehensive Federal Highway Administration (FHWA) research and development effort known as Demonstration Project No. 102 (DP-102) is designed to transfer this new advanced welding technology to state transportation agencies and bridge fabricators.
Due to its high deposition rate, ESW is considered the most productive welding process in joining thick components. Initially, when the process was introduced in the United States in the late 1960s, there was some obvious success. However, certain welding problems began to surface in terms of welding imperfections and inadequate properties which led in 1977 to FHWA placing a moratorium (FHWA Notice 5040.23) on the use of ESW for weldments on primary structural-tension bridge members. The notice effectively eliminated the use of ESW not only in bridge fabrication but in various other United States industries as well.
In the 1980s, FHWA launched a comprehensive research and development program to examine ESW technology. The main objectives of the program were to better understand the specifics of the ESW process and to advance the level of applied ESW technology. Generally, ESW operating procedures and weld properties were significantly improved as a result of the initial phase of this research program, which was conducted by the Pacific Northwest Laboratory, Richland, Wash., and the Oregon Graduate Institute of Science and Technology, Beaverton, OR. Foremost, the Narrow-Gap Improved (NGI) ESW technique an improved modification of ESW process was developed.
The NGI technique produces satisfactory welds and considerably improves Charpy V-notch (commonly referred to as "CVN") toughness. In the early 1990s, extensive field trials were conducted based on research findings. These trials were conducted at four bridge fabrication facilities and showed satisfactory results.
In September 1993, FHWA awarded a four-year contract to BIRL, Northwestern University's industrial research laboratory based in Evanston, Ill. A team of researchers led by Dr. Valdemar Malin and assisted by an advisory board of federal and state transportation officials and bridge and welding engineers from private industry worked in partnership.
FHWA's technical representative and program manager for this project is Krishna K. Verma, a welding engineer in the Bridge Division at FHWA headquarters in Washington, D.C.
For information about the demonstration project contact the FHWA Division Office in your state or call Mr. Verma directly at (202) 366-4601.
Krishna K. Verma is a welding engineer in the FHWA's Bridge Division. He has been responsible for overseeing the Bridge Weld Program, pertaining to the nation's steel bridges, since 1984.
The objectives of DP-102, "Narrow-Gap Improved Electroslag Welding for Bridges," include:
1. NGI ESW Equipment and Materials Availability.
2. Development of NGI ESW Documentation.
3. Verification of NGI ESW Procedure.
4. Verification of Toughness in NGI ESW Welds.
5. Transfer of New ESW Technology.
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