Piping Stress Analysis Skill
Purpose
The Piping Stress Analysis skill provides capabilities for analyzing piping system stresses per ASME B31 codes, ensuring code compliance and equipment protection through proper flexibility analysis.
Capabilities
- Piping flexibility analysis
- Thermal expansion stress calculation
- Support and restraint design
- Nozzle load verification
- Flange leakage assessment
- Code compliance verification (B31.1, B31.3)
- CAESAR II integration
- Piping isometric review
Usage Guidelines
ASME B31 Code Overview
Code Selection
| Code | Application | |------|-------------| | B31.1 | Power piping | | B31.3 | Process piping | | B31.4 | Liquid transportation | | B31.5 | Refrigeration piping | | B31.8 | Gas transmission | | B31.9 | Building services |
Stress Categories
B31.3 Stress equations:
Sustained stress:
S_L = (P*D)/(4*t) + (0.75*i*M_A)/Z <= S_h
Expansion stress:
S_E = sqrt(S_b^2 + 4*S_t^2) <= S_A
Occasional stress:
S_L + S_occ <= k*S_h
Where:
P = pressure
D = outside diameter
t = wall thickness
i = stress intensification factor (SIF)
M_A = sustained moment
Z = section modulus
S_h = hot allowable stress
S_A = allowable stress range
k = occasional load factor
Thermal Expansion Analysis
Thermal Movement
Linear expansion:
delta_L = alpha * L * (T2 - T1)
Where:
alpha = coefficient of thermal expansion
L = pipe length
T2 - T1 = temperature change
Typical alpha values (in/in/F):
Carbon steel: 6.5 x 10^-6
Stainless steel: 9.5 x 10^-6
Copper: 9.3 x 10^-6
Flexibility Analysis
Key principles:
1. Piping expands when heated
2. Expansion induces stress if restrained
3. Flexibility (bends, loops) reduces stress
4. Over-constrained systems have high stress
5. Under-constrained systems have excessive movement
Stress Intensification Factors
Common SIF Values
| Component | i-factor (approx) | |-----------|------------------| | Straight pipe | 1.0 | | Long radius elbow | 0.9/h^(2/3) | | Short radius elbow | 0.75/h^(2/3) | | Miter bend (1 cut) | 1.52/h^(5/6) | | Welding tee | 0.9/h^(2/3) | | Reinforced fabricated tee | Variable | | Branch connection | Variable |
Flexibility characteristic:
h = t*R/(r^2)
Where:
t = wall thickness
R = bend radius
r = mean radius of pipe
Support Design
Support Types
| Type | Restrains | Allows | |------|-----------|--------| | Rest (shoe) | Vertical down | Horizontal, vertical up | | Guide | Lateral | Axial, vertical | | Anchor | All directions | None | | Rod hanger | Vertical | Horizontal | | Spring hanger | Vertical (variable) | Horizontal | | Constant hanger | Vertical (constant) | Horizontal |
Support Spacing
Suggested maximum spans (B31.1):
| Pipe Size | Water (ft) | Steam/Gas (ft) |
|-----------|------------|----------------|
| 1" | 7 | 9 |
| 2" | 10 | 13 |
| 4" | 14 | 17 |
| 6" | 17 | 21 |
| 8" | 19 | 24 |
| 12" | 23 | 30 |
Nozzle Loads
Equipment Protection
Nozzle load limits:
- Equipment vendor provides allowables
- Common standards: API 610, API 617, NEMA SM23
- Consider sustained and thermal loads separately
- Combined loads may use interaction formula
Typical check:
sqrt((F_x^2 + F_y^2 + F_z^2)/(F_allow^2) +
(M_x^2 + M_y^2 + M_z^2)/(M_allow^2)) <= 1.0
Load Combinations
Operating case:
W + P + T + D
Hydrotest case:
W + H + D
Where:
W = Weight
P = Pressure
T = Thermal
D = Displacement
H = Hydrotest pressure
Flange Leakage
Assessment Methods
ASME B16.5 flange rating:
- Check P-T rating at operating conditions
- Include pressure equivalent from moments
Equivalent pressure method:
P_eq = P + (16*M)/(pi*G^3)
Where:
M = bending moment at flange
G = flange gasket diameter
NC(T)MF method:
Uses ASME VIII Appendix 2 calculations
More accurate for high moment cases
Modeling Guidelines
Model Building
Key elements:
1. Include all pipe runs
2. Model equipment properly (rigid/flexible)
3. Define support locations accurately
4. Include all branch connections
5. Apply correct operating conditions
6. Model spring hangers if used
Operating Cases
| Case | Temperature | Pressure | Weight | Use | |------|-------------|----------|--------|-----| | Sustained | Ambient | Design | Full | Code check | | Operating | Operating | Operating | Full | Equipment loads | | Thermal | Operating-Ambient | None | None | Expansion stress | | Hydrotest | Ambient | Test | Full + Water | Support design |
Process Integration
- Related to structural analysis for piping systems
Input Schema
{
"piping_system": {
"line_number": "string",
"code": "B31.1|B31.3",
"material": "string",
"size": "string (NPS)",
"schedule": "string"
},
"operating_conditions": {
"design_pressure": "number (psig)",
"design_temperature": "number (F)",
"operating_pressure": "number (psig)",
"operating_temperature": "number (F)"
},
"geometry": {
"isometric": "file reference",
"length": "number (ft)",
"elevation_change": "number (ft)"
},
"equipment_connections": [
{
"equipment": "string",
"nozzle": "string",
"allowable_loads": "object"
}
]
}
Output Schema
{
"stress_results": {
"code_compliance": "pass|fail",
"sustained_stress": {
"max_value": "number (psi)",
"allowable": "number (psi)",
"location": "string",
"ratio": "number"
},
"expansion_stress": {
"max_value": "number (psi)",
"allowable": "number (psi)",
"location": "string",
"ratio": "number"
}
},
"nozzle_loads": [
{
"equipment": "string",
"forces": "array [Fx, Fy, Fz]",
"moments": "array [Mx, My, Mz]",
"compliance": "pass|fail"
}
],
"support_schedule": [
{
"location": "string",
"type": "string",
"load": "number (lb)"
}
],
"thermal_movements": {
"max_displacement": "number (in)",
"location": "string"
},
"recommendations": "array"
}
Best Practices
- Start with proper piping layout for flexibility
- Verify equipment nozzle allowables early
- Include all weight loads (insulation, contents)
- Model actual support conditions
- Check flange ratings at all operating conditions
- Document all assumptions and simplifications
Integration Points
- Connects with Pressure Vessel Design for equipment interface
- Feeds into Support design for structural requirements
- Supports FAI Inspection for as-built verification
- Integrates with Design Review for approval