Q: What corrosion rates affect unpainted A36 in coastal environments?
A: Rates average 5–8 mils/year (0.13–0.2 mm) within 5 miles of seawater. Chloride deposition accelerates pitting, reducing thickness by 30% in 10 years. Relative humidity >60% enables galvanic corrosion with dissimilar metals. Sheltered areas suffer crevice corrosion at 2× exposed surfaces. Life expectancy is <15 years without protection.
Q: How does hot-dip galvanizing protect A36 angles?
A: Zinc coating (3.9–7 mils) provides barrier and sacrificial protection. Alloy layers bond at 842°F (450°C) during immersion. Service life equals 1.7× coating thickness (years) in rural atmospheres. Grinding/zinc-rich paint repairs damaged zones. Vent/drain holes prevent trapped acid during dipping.
Q: When is thermal spray metallization preferred over galvanizing?
A: For sections >40 ft long (tank limits) or post-fabrication repairs. Aluminum or zinc-aluminum coatings offer 50-year life in industrial zones. No distortion risk versus hot-dip. Adhesion exceeds 1,500 psi with proper blasting. Complex geometries achieve uniform coverage.
Q: What paint systems suit A36 in chemical plants?
A: Epoxy primers (75–125 μm) with polyurethane topcoats (50–75 μm) resist solvents and UV. Zinc-rich epoxies add cathodic protection. Total DFT of 200–250 μm ensures 15+ years service. Abrasion-resistant formulations handle particulate erosion. Inspection includes holiday detection at 67.5 kV.
Q: How does weathering steel (e.g., A588) outperform A36 in corrosion?
A: A588 forms stable rust patina (Cu-P-Cr alloy) halting corrosion at 1–2 mils after initial loss. Uncoated life exceeds 50 years in non-marine atmospheres. Higher strength (50 ksi yield) allows thinner sections. Cost premium of 20–30% offsets lifetime maintenance. Unsuitable for chloride-rich or stagnant-water environments.
