Thermal Expansion Coefficient of Carbon Steel

A 100 m steel pipe run heated 100 °C grows 117 mm: the length of a fist. That is the entire reason for expansion loops, guides, anchors and bellows in piping, and for expansion joints in bridges and rails. Restrain the same steel completely and you get thermal stress σ = E α ΔT, which for 100 °C is 200e9 × 1.17e-5 × 100 = 234 MPa: enough to yield A36 outright, with no external load at all. Note that this stress is independent of length and cross-section, which surprises people every time.

The coefficient itself is stable and unglamorous, carbon steel varies by only a few percent across grades, but the companion values are not. Austenitic stainless expands about 30 % more at room temperature, aluminium twice as much, and PVC about four and a half times as much, so dissimilar-material assemblies are where expansion causes trouble: stainless pipe on carbon steel supports, aluminium cladding on steel framing, plastic pipe in a metal hanger system. Concrete is the fortunate exception, expanding at almost exactly the same rate as steel, which is what makes reinforced concrete possible at all.