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SteelOnline self-study

Weathering Steel and Corrosion Protection of Steel Bridges

1 PDH · about 60 minutes · Course no. BR-ST02 · Instructor: Michael Craig, PE

About the instructor

Michael Craig, PE is Senior Vice President and Southeast Director at Strinteg Corporation, leading bridge inspection and structural engineering across eight states and Puerto Rico. In 27+ years he has inspected over 4,000 structures and completed 3,000+ load ratings and 160+ load tests. He has managed repair and preservation design for complex bridges, including cable-stayed bridges. He holds PE licenses in twelve states, DC and Puerto Rico, SPRAT Level 1, and FAA Part 107 credentials.

Corrosion is the main long-term enemy of steel bridges, and the owner has two basic strategies against it: let a weathering-grade steel protect itself with a stable oxide patina, or put a barrier or sacrificial coating between the steel and the environment. This course covers both. It explains how the weathering steel patina forms and why it fails in wet, salty or sheltered conditions; summarizes the siting, detailing and maintenance guidance in FHWA Technical Advisory T 5140.22 (1989) and the July 19, 2023 FHWA memorandum on follow-up actions for uncoated weathering steel bridges issued after the Fern Hollow Bridge collapse; compares zinc-rich paint systems, thermal-spray metalizing and hot-dip galvanizing using the FHWA Steel Bridge Design Handbook corrosion-protection volume; and closes with inspection and preservation of protection systems using the FHWA Bridge Preservation Guide (2018). Numerical guidance quoted in the course is attributed to its source; worked numbers in the examples are illustrative and computed for this course, not from a real bridge.

⬇ Download study guide (PDF)

Learning objectives

  • Explain how weathering steel patina forms
  • Identify environments where it performs poorly
  • Compare coating systems
  • Inspect and maintain protection systems

Outline

  1. Why steel bridges corrode
  2. Two strategies: patina or coating
  3. The protection system is part of the structure
  4. How the weathering steel patina forms
  5. What good and bad patina look like
  6. Corrosion-rate benchmarks from the handbook
  7. T 5140.22: where weathering steel struggles (environment)
  8. T 5140.22: where weathering steel struggles (location and geometry)
  9. Detailing: keep water off the steel
  10. Detailing: traps, boxes, overlaps and staining
  11. Coating systems: from lead alkyd to zinc-rich
  12. Metalizing and galvanizing
  13. Comparing options: first cost and life-cycle cost
  14. Fern Hollow and the July 2023 FHWA memorandum
  15. Inspecting protection systems
  16. Maintaining and preserving protection systems
  17. Case study: a weathering steel overpass
  18. Open the course (23 screens, 2 knowledge checks)
  19. Final quiz — 10 questions, 70% to pass

References

  1. FHWA Technical Advisory T 5140.22, Uncoated Weathering Steel in Structures, 1989
  2. FHWA, Steel Bridge Design Handbook, FHWA-HIF-16-002 (multi-volume), 2015
  3. FHWA, Bridge Preservation Guide: Maintaining a Resilient Infrastructure to Preserve Mobility, FHWA-HIF-18-022, 2018
  4. FHWA, Memorandum: ACTION: Inspection Finding Follow-up Actions for Uncoated Weathering Steel Bridges, J. L. Hartmann, July 19, 2023 (fhwa.dot.gov/bridge/inspection/Memo_July2023_UWS.cfm)
  5. FHWA, Steel Bridge Design Handbook: Corrosion Protection of Steel Bridges, FHWA-HIF-16-002 Vol. 19, 2015 (rosap.ntl.bts.gov/view/dot/49758)
  6. NTSB, Improving the Identification, Prioritization, and Completion of Follow-up Actions on Bridges with Uncoated Weathering Steel Components, Interim Report NTSB/HIR-23-07, May 18, 2023 (as summarized in the FHWA July 2023 memorandum)