When corrosion resistance, cleanability or appearance is the requirement. Carbon steel is substantially cheaper and is the correct default for concealed structure. Stainless earns its cost in exposed external work, coastal and chloride environments, food, beverage and pharmaceutical equipment that is washed down, laboratory and process installations, and architectural applications where the section is visible and unpainted.

304 for general internal use and mild external exposure. 316 where chlorides are present, which includes coastal locations, swimming pools, areas exposed to de-icing salt and many process environments, since its molybdenum content resists pitting. Duplex grades where higher strength allows a lighter section, or where stress corrosion cracking is a risk. Grade should follow the exposure rather than habit.

Welded sections are formed from strip and joined by a longitudinal weld, then sized and usually heat treated; they cover the large majority of structural and architectural use and are considerably cheaper. Seamless sections are produced without a weld and are specified for high-pressure and high-integrity applications where a weld line is unacceptable. For most building and equipment work, welded is entirely appropriate.

Because on exposed work the finish is the product. Mill finish is acceptable where the section will be concealed or coated. Brushed and polished finishes are specified for handrails, balustrades, shopfitting and visible structure, and the condition of the weld seam must be stated separately, since a seam that is structurally irrelevant is a visible defect on a handrail. Finish also affects cleanability in hygienic applications.

Circular sections have equal properties in all directions and the best torsional stiffness, and present a uniform appearance from any angle. Square sections have flat faces that make connections, fixings and cladding attachment much simpler. Rectangular sections have different stiffness about each axis, which suits members bending predominantly in one plane. Choose on connection detailing and loading direction as much as on appearance.

Not as extensively. The range of sizes, wall thicknesses and lengths is narrower, availability is more variable and lead times are longer, particularly in 316 and duplex and in larger sizes. This should be checked early in design rather than assumed, since substituting a different size late can affect connection details and appearance across a whole assembly.

Stainless work-hardens and has lower thermal conductivity than carbon steel, so cutting and drilling need sharp tools, positive feed and slower speeds. Welding requires matched consumables, back purging on critical joints and post-weld cleaning, since heat tint left in place reduces corrosion resistance. Tools and abrasives used on carbon steel must not be used on stainless, because embedded iron particles cause rust staining.