Pipe Stress & Flexibility

Q: Which standards or codes apply?

ASME B31.3 (flexibility & stress, displacement-stress range SA), Caesar II (formal analysis), API 610/617 (nozzle loads), EJMA (expansion joints).

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Quick pick (TL;DR)

Compute thermal growth ΔL = α·L·ΔT.
Absorb it with a change of direction (leg), an expansion loop, or — only where layout forbids — an expansion joint (bellows).
Screen flexibility with the guided-cantilever leg L = √(3·E·D·ΔL / Sb); if the layout gives less than that, add a loop or run formal analysis (Caesar II).
Always check the resulting loads on equipment nozzles against the vendor's allowables.

Step 1 — Ways to absorb growth

Method	Use when	Note
Direction change	Natural in layout	Preferred
Expansion loop	Long straight runs	No moving parts
Expansion joint	No space	Last resort

Step 2 — Worked flexibility screen

6″ CS, 30 m, 20→250 °C

Step 1 — Thermal growth ΔL = α · L · ΔT ΔL = 11.7e-6 × 30 × (250−20) ΔL = 11.7e-6 × 30 × 230 = 0.0807 m ΔL = 80.7 mm Step 2 — Required leg L = √(3·E·D·ΔL / Sb) E = 203,000 MPa , D = 168.3 mm , Sb = 103 MPa L = √(3×203000×168.3×80.7 / 103) L = √(8.03×10⁷) = 8.96 m Step 3 — Compare offset leg available 4 m < 8.96 m → too stiff → add expansion loop or formal analysis Answer → expansion loop, then verify in Caesar II

Guided-cantilever gives the leg needed — a screening tool; shorter offset → loop or formal Caesar II.

Step 3 — Supports & loads

Anchors + guides direct growth; never trap a hot run.
Check nozzle loads to API 610/617.
Spring hangers for vertical movement.

Thermal growth & flexibility calculator

Growth + guided-cantilever leg

ΔL = α·L·ΔT; leg = √(3·E·D·ΔL / Sb).

Run length L (m)

ΔT (°C)

α (1/°C)

OD D (mm)

E (MPa)

Sb (MPa)

Offset available (m)

Screening — if the offset is too short, add a loop or run Caesar II.

Common mistakes

Trapping a hot line with no flexibility.
Expansion joint as a shortcut.
Skipping formal analysis where needed.

Requisition & datasheet

Material, size, length, temperatures.
Growth, leg, method, nozzle check.

Frequently asked questions

What should I know about Pipe Stress & Flexibility?

Compute thermal growth ΔL = α·L·ΔT. Absorb it with a change of direction (leg), an expansion loop, or — only where layout forbids — an expansion joint (bellows). Screen flexibility with the guided-cantilever leg L = √(3·E·D·ΔL / Sb); if the layout gives less than that, add a loop or run formal analysis (Caesar II). Always check the resulting loads on equipment nozzles against the vendor's allowables.

Which standards or codes apply?