Weldability of Bridge Steel with Protective Coatings

In 2020 the American Association of State Highway and Transportation Officials/American Welding Society (AASHTO/AWS) D1.5 Bridge Welding Code adopted a new sub clause, 5.2.4.2., that allows welding over protective coatings. Applicable protective coatings common on steel bridges include paint, hot-dip galvanizing, and thermal-spray metallizing. According to Linnert (1995), problems with welding over coatings include, “weld cracking, blowholes in the weld metal, pollution of the work place, damage to the surface appearance, excessive deterioration of welding electrodes, and the inability to join parts using any of the welding processes.” Weld defects can be especially problematic when not visible on the exterior surface of the weld. Furthermore, AASHTO/AWS D1.5 does not specify limitations to welds over coatings except for web-to-flange connections and joints subjected to calculated tensile stress, as long as they meet the “other weld quality requirements of this code”. The AASHTO/AWS D1.5 Bridge Welding Code is required by the Federal Highway Administration for use with all bridge welding on ASTM A709 steel. Shielded metal arc welding (SMAW), flux-cored arc welding (FCAW) and arc-stud welding (SW) are considered as common welding processes for steel bridge construction under field welding conditions. AWS D19.0-72 Welding Zinc-Coated Steel, published in 1972, represents the most comprehensive guideline on welding over zinc coated steel. Arc disturbance, formation of undercut and porosity are common problems associated with shielded metal arc welding (SMAW) over zinc coated steel. Flux-cored arc welding was not considered in the document. Arc blow, i.e. piling up of weld metal to one side was associated with stud welding over zinc coatings. The current edition of AASHTO/AWS D1.5 does not specifically prohibit welding shear studs over steel coatings, but article 9.4.3 states the “areas to which the studs are to be welded shall be free from scale, rust, moisture, and other injurious material to the extend necessary to obtain satisfactory welds”. A coating would be considered an “injurious material” if quality welds could not be produced. Both fabricators and contractors have an interest in welding over coatings as it applies to both shop and field welding of new and in-service bridges. Before adopting the new welding code provision, it needs to be evaluate if this practice will produce acceptable quality welds. If acceptable welds can be produced, any limitations need to be defined. Lack of quality welds over coatings affects the serviceability of both new steel bridges and any repaired steel bridges. Significant costs and disadvantages could be encountered if weld defect problems related to the new code provision were to arise in bridges. Contractors also weld temporary supports on galvanized pier pipe piles. Contractors are supposed to remove the coating before welding. However, Alaska Department of Transportation and Public Facilities (Alaska DOT&PF) would benefit from knowing how detrimental these welds could be to the pipe pile base metal if the coating is not removed prior to welding. The goal of this research program is to determine the extent to which the thickness and type of zinc-coating influence the production of acceptable welds on structural steels used for bridge construction. Specific objectives are (1) to compare weld quality of flux-cored arc welded (FCAW) and arc-stud welded (SW) joints on zinc-coated steel to those on uncoated steel, (2) to evaluate the effect of coating type and thickness on weld quality, (3) to evaluate the mechanical properties of welds on zinc-coated steel containing defects, (4) to evaluate the propensity for zinc penetration cracking, and (5) to identify limitations and/or specific requirements for welding over protective coatings that would be required to produce acceptable welds.

Language

• English

Project

• Status: Active
• Funding: $301503
• Sponsor Organizations:

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Managing Organizations:

  Alaska Department of Transportation and Public Facilities RD&T2

  3132 Channek Dr.
  Juneau, AK  United States  99801
• Project Managers:

  Bosin, Anna

• Performing Organizations:

  Ohio State University

  Columbus, OH  United States 
• Principal Investigators:

  Fink, Carolin

• Start Date: 20240108
• Expected Completion Date: 20251231
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Bridge construction; Coatings; Cracking; Steel bridges; Thickness; Welding
• Subject Areas: Bridges and other structures; Construction; Highways;

Filing Info

• Accession Number: 01904774
• Record Type: Research project
• Source Agency: Alaska Department of Transportation and Public Facilities
• Files: RIP, STATEDOT
• Created Date: Jan 17 2024 4:26PM