Winter 1996
Vol. 59· No. 3

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.
An important task for acceptance of NGI ESW is to ensure that the required equipment and materials be commercially available to users for making production welds.

2. Development of NGI ESW Documentation.
A comprehensive package of specifications and guides required by FHWA is being developed by BIRL and is close to completion. The guides contain technical, procedural, and training information on NGI ESW. Proposed specifications (code requirements) are oriented toward inclusion into ANSI/AASHTO/AWS Dl.5 Bridge Welding Code.

3. Verification of NGI ESW Procedure.
The equipment, the new electrode wire, the flux formulation, and the recommended NGI ESW procedure, have to be tested. This is crucial for the implementation of the new technology. The laboratory trials conducted at BIRL's welding laboratory have proven that acceptable electroslag welds can be produced on a regular basis.

4. Verification of Toughness in NGI ESW Welds.
Testing during the demonstrations will prove that acceptable toughness of electroslag welds can be produced on a regular basis.

5. Transfer of New ESW Technology.
To methodically transfer the new ESW technology to state transportation agencies, bridge fabricators, and FHWA representatives, relevant information on the NGI ESW technique will be disseminated and actual ESW-making would be demonstrated. The NGI ESW demonstrations started in September 1995 and will be presented in various locations in the United States. During the demonstration phase, a plan is in place to record on videotape the training materials on NGI ESW for future use by state agencies, fabricators, and others.