Jim Talbot Electroslag welding is faster than typical methods.

An improved version of electro-slag welding, a technique once banned by the Federal Highway Administration, is being used on a $205-million Tampa interchange upgrade for the Florida Dept. of Transportation. The method, dubbed Narrow Gap Improved Electroslag Welding, welds two plate girders in a single pass without preheating.

Florida Structural Steel, Tampa, is using the NGI-ESW method on six of 10 girder bridges for the State Route 60 interchange near the airport, says Dale Ison, manufacturing manager for Florida Structural Steel. Ison estimates splicing 2-in.-thick, 24-in.-wide plates would take about 22 hours by conventional welding. An electroslag weld would be ready for testing in six to seven hours.

Arcmatic

Traditionally, welders employ a submerged-arc welding process for butt joints. This requires multiple passes with the arc submerged under a granular flux. Electroslag welding involves a single-pass, continuous process, according to manufacturer Arcmatic Welding Systems, Vallejo, Calif. Two steel plates are positioned 3⁄4 in. apart, creating the “narrow gap” in which the welding will occur. A welding arc heats a supply of granular flux and forms an electrically charged, molten slag bath maintained at about 3,500°F hot enough to sustain continuous melting of the welding wire without a continuing arc. The slag bath and molten puddle create a vertical weld that moves upward through the gap.

Electroslag welding was used on bridges from the late 1960s until 1977, when a large crack was found on an electroslag-welded repair on the Neville Island Bridge near Pittsburgh. FHWA then prohibited electroslag welding on main structural tension members.

FHWA-sponsored research led to the new method, including a narrower gap and higher current. It has “resulted in improved weld reliability and toughness and virtually eliminated internal flaws,” according to FHWA, which lifted the moratorium in 2000. The method is still limited to a maximum 3-in. plate thickness and is not allowed on fracture-critical girders or in harsh temperature zones.

Last year, FDOT changed its structural steel codes to allow electroslag welding, opening the door for Florida Structural Steel to proceed with the method on the Tampa project. “This [job] has 400 girders on it, and 1,600 butt splices,” says Jamie Hilton, steel group manager for KTA-Tator, Pittsburgh, the commercial inspector. “This is ideal for that type of situation.” FHWA requires the welds to undergo 100% inspection.

Ison estimates cost and setup of the machinery from Arcmatic at $125,000, plus $60,000 for materials and labor to build a flange-welding jig. He hopes to use the method on future jobs.

Jim Talbot FDOT allows weld method on spans.

Steel experts say electroslag welding has a lower failure rate than manual welds. “[Electroslag] gives greater accuracy and uniformity in a controlled environment,” says Conn Abnee, executive director of the National Steel Bridge Alliance.

Despite the lifted moratorium, few states or fabricators have embraced NGI-ESW. The American Welding Society’s codes don’t yet include it, says Ison. Society spokesperson Adrienne Zalkind says it is being discussed for the sixth edition of the codes, slated for release in 2009.

Bill Adams, senior project manager with Parsons Brinckerhoff’s Tampa office, the construction engineer/inspector, notes that if something happens, like a power loss, the bad joint has to be cut out altogether and rewelded. With traditional welds, if a spot is bad, the welder can cut out that area and fix it.