Thermal expansion compatibility

CTE mismatch checker (dissimilar metals)

The check engineers run before pairing austenitic SS bolts in a CS flange (or CS piping clamped onto a Ti vessel nozzle). Computes ΔL across two metals over a service excursion and the restraint stress that develops when the joint is rigid.

Inputs

Metal A

Metal B

Ambient T_amb°C

Hot T_service°C

Reference lengthmm

Tube bundle length, flange-to-flange, etc.

Average modulus E_avgGPa

For restraint-stress estimate. CS ~200, SS ~195, Al ~70, Ti ~110.

Results

α_A (316 / 316L austenitic)16.56×10⁻⁶/°C

α_B (Carbon steel (A36 / A516))12.38×10⁻⁶/°C

Δα (A − B)4.19×10⁻⁶/°C

α ratio (A/B)1.34

Expansion of A over ΔT5.466mm

Expansion of B over ΔT4.084mm

Differential ΔL = A − B1.382mm

Rigid-restraint σ ≈ E·Δα·ΔT276MPa

VerdictHIGH MISMATCH — joint stress > 200 MPa, expect cracking / leak

The "rigid restraint" stress is an upper-bound — real joints have flexibility (gasket compression, bolt stretch, pipe flexibility) that softens the load. For HEX tubesheets the differential between tubes and shell drives bowing; for dissimilar welds (austenitic + ferritic) it drives thermal- cycle fatigue at the fusion line — use a Ni-base buffer (Inconel 182/82) to bridge.

Download all inputs + calculations + outputs as a single PDF.