Narrow-Gap Improved Electroslag Welding for Bridges (NGI ESW)

The National Bridge Research Organization (NaBRO) at UNL, in the framework of its Technology Transfer mission, and FHWA sponsored a three-day workshop on an emerging welding technology. It is anticipated that this new approach will have a major impact on the construction of steel bridges in the years to come. The workshop took place in Lincoln, Nebraska, during the first week in December where Dr. Bill Wood and Mr. Bob Turpin of the Oregon Graduate Institute elaborated on and demonstrated the new welding process.

The new welding technology is the Narrow Gap Improved Electroslag Welding (NGI-ESW) and is a modified version of the conventional electroslag welding (ESW) process. In the early 1970's, the conventional ESW became a dominant process in the fabrication of bridges. By 1974, in Michigan alone, there were 125 bridges fabricated using ESW. After a large crack was found in an ESW repair on the Neville Island Bridge near Pittsburgh though, the FHWA prohibited the use of ESW for bridge tension members.

In the 1980's, the Oregon Graduate Institute of Science and Technology developed the new Narrow Gap Improved Electroslag Welding (NGI ESW) process. The new approach is a single-pass vertical welding process. The NGI ESW process shows improvements regarding the welding variables, grain structure, microstructure, and toughness of the weld. The field trials performed in the early 1990's by the FHWA produced satisfactory results for shop use, produced welds of high integrity and provided weld toughness that met the requirements of the ANSI/AASHTO/AWS D1.5 Bridge Welding Code.

Consequently, after favorable testing, the FHWA is pursuing transferring the new and improved ESW technology to State DOT's and bridge fabricators. The FHWA is expected to lift the moratorium if the demonstrations are proved favorable for use in state projects across the country.