Changing the way they do business
Bridge, structural fabricators have to think about process choices
Dealing with work loads, delivery schedules, and many other responsibilities doesn't leave managers with much time to consider factors that justify equipment improvements.
Dealing with work loads, delivery schedules, and many other responsibilities doesn't leave managers with much time to consider factors that justify equipment improvements. Often this means ideas for improvements get shelved. However, fabricators who want to improve production and competitiveness can consider several processes for their projects.
Today bridge and structural fabricators take advantage of the high deposition rates offered by the following welding processes:
- Submerged arc welding (SAW) gantry units
- Low-alloy cored (LAC) low-alloy SAW
- Advanced SAW controllers
- Robotic flux-cored arc welding
- Narrow-gap improved electroslag welding
- Tandem-pulse gas metal arc welding
Structural and bridge fabricators traditionally have not employed welding engineers and instead have delegated responsibilities for alternative equipment or process improvements to the quality control department or the welding foreman. These individuals frequently either are not experienced enough with or are reluctant to pursue automated welding processes, with the exception of SAW.
The numerous specific requirements that either exempt or limit some welding processes has influenced this trend. For example, some state departments of transportation (DOTs) do not permit the use of FCAW for primary welded bridge members, because some lack confidence in the process and others have had bad experiences with a specific fabricator or project.
For the DOTs that permit FCAW, the fabricator must perform two procedure qualification records (PQRs) except when fabricating ancillary products. While other options exist, this typically is the most popular choice.
AWS D1.1 gives prequalified status to the FCAW process. The bridge welding code states that fillet weld mechanical properties are based on groove weld testing. This can be a difficult engineering and metallurgical concept to comprehend.
The testing required to permit a fabricator to conduct vertical-up fillet welding on stiffener to flanges would require a 3G vertical-up procedure test, complete joint penetration with nondestructive testing (NDT), and destructive testing.
Bridge fabricators question the validity of the multiple-pass PQR test on groove-welded plates, which can qualify for the typical single-pass fillet welds made using FCAW.
This, along with several other paragraphs in the bridge welding code, has presented concerns and questions for fabricators, third-party inspectors, and state DOT representatives. Like most standards and codes, it may be a subject of potential code revision for the next code publication by the AWS D1 Committee and/or D1.5 subcommittee, as appropriate.
For more information on weld process advancements and automation for the bridge and structural fabrication industry, see Steven T. Snyder's related article, "Building a better weld process: Bridge and structural fabricators have options," in the November/December 2001 issue of Practical Welding Today.
For more information on codes and standards for bridge and structural fabrication, contact the American National Standards Institute, 1819 L St., N.W., Washington, DC 20036, phone 202-293-8020, fax 202-293-9287, Web site www.ansi.org.
For additional information on state highway and transportation regulations, contact the American Association of State Highway & Transportation Officials, 444 N. Capitol St., N.W., Suite 249, Washington, DC 20001, phone 202-624-5800, fax 202-624-5806, e-mail firstname.lastname@example.org, Web site www.aashto.org.
For more information on welding codes and standards, contact the American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126, phone 800-443-9353, fax 305-443-7559, e-mail email@example.com, Web site www.aws.org.
Federal Highway Administration, "Proposed Specifications for Narrow-gap Improved Electroslag Welding," (Washington, DC: FHWA, 1999), page 1, paragraph 16.
"Electroslag welding stands poised for a comeback in bridge construction: The Federal Highway Administration is in the process of ending the ban prohibiting electroslag welding from use on tension members of steel," Welding Journal, (February 2000), pp. 39-41.