How can inspectors differentiate carbon steel from weathering steel or stainless steel on-site?

• A. All steels look the same on-site.
• B. Weathering steel develops a protective patina and rust color; stainless steel shows minimal corrosion; coatings and label information also help.
• C. Carbon steel always looks the same color.
• D. Only the weight distinguishes them.

Answer: (B)

Inspectors can tell steel types apart on-site by looking at surface behavior and available labeling. Weathering steel is known for forming a distinctive orange-brown patina that acts as a protective layer; this patina is a telltale sign you’re dealing with weathering steel, and you’ll see its characteristic rust coloration on unpainted sections. Stainless steel resists corrosion, so you typically observe little to no rust and a more neutral gray to shiny surface, though in harsh environments some staining or minor surface discoloration can occur. Carbon steel, when exposed and uncoated, tends to rust readily, showing brighter orange-red rust patches where protection is lacking.

Coatings such as paint or other protective layers can hide the base metal’s appearance, so inspectors also rely on labels, stamps, or manufacturer data plates that indicate the material or grade. Using a combination of surface cues (patina vs. corrosion behavior) and available labeling or coating information provides the most reliable on-site differentiation.