Stress

Module from the Piping Engineering Curriculum curriculum.

Module 7 — Pipe Supports & Stress Analysis · Learning Objectives · 1. Apply B31.3 §319 allowable stress ranges (SA and SL limits) · 2. Distinguish primary (sustained) vs secondary (displacement) loads · 3. Select support type: shoe, guide, anchor, spring, snubber, strut · 4. Size expansion loops for thermal growth using simple geometry · 5. Identify when CAESAR II or AutoPIPE analysis is required · When is Stress Analysis Required?

Trigger	Action	Reference	Notes	Criticality	Typical
Δ T > 200 °F between install and operate	Formal analysis	B31.3 §319.4.1	Thermal growth drives loads	High	Most hot service
NPS ≥ 4 and hot (> 250 °F)	Formal analysis	Owner spec	Economic threshold	Medium	Most refinery
Connection to rotating equipment	Formal + nozzle loads	API 610/617/618	Check against allowables	High	Always
Connection to tank nozzle	Formal	API 650 App. P	Settlement & thermal	Medium	Always
High pressure (Class ≥ 900)	Formal	B31.3 Ch. IX	Stress-intensification factors	High	Always
Cryogenic	Formal	B31.3 §323.2.2	Large ΔT; brittle risk	High	Always
Small-bore vibration risk	Check w/ screening	Energy Institute AVIFF	Fatigue cracks	Medium	Frequent failure mode
Support Selection Matrix
Support Type	Function	Allows	Restrains	Typical Spacing NPS 6 CS	Notes
Shoe (rest)	Vertical support	Axial, transverse, rot	Vertical	17 ft at 400 °F water	Most common
Guide	Lateral restraint	Axial, vertical	Transverse	2x shoe spacing	Prevents buckling
Anchor	Full restraint	None	6 DOF	Strategic	End of loop
Spring hanger (variable)	Thermal growth	Vertical movement	Partial weight	Hot piping	Calculate hot/cold load
Constant-effort hanger	Large thermal	Vertical	Full load throughout	Δ > 2 in	More expensive
Snubber	Dynamic restraint	Slow thermal	Fast seismic/surge	Per seismic analysis	Slide-blocking device
Rigid strut	Directional	Perpendicular	2-way	Dynamic	—

Source: Piping_Engineering_Curriculum_v1.xlsx · Sheet: Stress

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