เครื่องคำนวณการขยายตัวทางความร้อนและความยืดหยุ่นของท่อ

The classic guided cantilever formula for expansion loop leg length is:

L_loop = √(3 × E × D × Δ / S_a)

Where E is the elastic modulus (MPa), D is pipe OD (mm), Δ is thermal expansion (mm), and S_a is allowable stress range (MPa). This gives the minimum loop leg length in mm. It comes from the guided-cantilever bending stress σ = 3·E·D·Δ/L².

An expansion loop is needed when the thermal expansion of a straight pipe run would cause stresses exceeding the allowable range. As a rule of thumb, any run over 10 m with ΔT > 50°C should be checked. The fully restrained thermal stress σ = E·α·ΔT must be compared to the allowable stress.

Alternatives include:

• Bellows expansion joints — compact but require maintenance
• Slip joints — for large movements
• Natural flexibility — using existing direction changes (L-bends, Z-bends)
• Flexible pipe sections — braided hose for small sizes

Both are piping design codes. EN 13480 is the European metallic industrial piping standard, ASME B31.3 is the American process piping code. Both require flexibility analysis but use slightly different allowable stress formulations. The expansion loop formula is the same engineering principle in both.

CTE (Coefficient of Thermal Expansion, α) is a material property that defines how much a material expands per unit length per degree of temperature change. Higher CTE means more expansion. Stainless steel (α ≈ 17.3) expands about 44% more than carbon steel (α ≈ 12.0) for the same temperature change.