Some projects require multiple design codes for different piping sections.
Common scenarios include:
Different codes may require unique load cases, safety factors, and material properties.
PASS/START-PROF provides three approaches for code combination.
Option 1: Approximate Method
This quick method provides approximate results.
Place anchors at code transition points. Analyze the first section in one project file using Code A.
Analyze the second section in a separate project file using Code B.
This approach ignores interaction between sections but works for preliminary analysis.
Option 2: Sequential Stiffness Method
Ideal for systems combining rigid (steel) and flexible (plastic/GRP) materials.
Model the steel piping with free ends at plastic connection points.
Run analysis and record connection point displacements: DX, DY, DZ, RX, RY, RZ.
Model the plastic piping with anchors at connection points.
Apply the recorded displacements to these anchors as boundary conditions.
This method works when steel stiffness significantly exceeds plastic stiffness.
Option 3: Full Integration Method
This approach provides the most accurate results.
Step 1: Select primary code (e.g., ASME B31.1). Model the entire system.
Step 2: Copy material properties from secondary code database to primary database.
For plastic sections in steel models, create custom materials with correct modulus and expansion properties.
Step 3: Create duplicate model with secondary code (e.g., ASME B31.3).
Copy or create materials for sections governed by the primary code.
Step 4: Use the Line List window to review results for each code section separately.
Code variations significantly impact analysis results due to:
1. Flexibility Factors and Load Cases
Bend and tee flexibility factors differ between codes, affecting stress distribution.
Load case combinations (operational, thermal, seismic) vary by code standard.
2. Safety Factor Requirements
Codes apply different safety factors to load categories.
Weight multipliers (pipe: 1.1, insulation: 1.2, etc.) affect support load calculations.
3. Material Property Definitions
Elastic modulus, allowable stresses, and thermal expansion coefficients may differ for identical materials between codes.
4. Recommended Practice
Perform separate analyses using each applicable code with proper material definitions.
Option 3 ensures accurate accounting of flexibility factors, safety criteria, and material properties.
Combine results from multiple analyses to verify compliance across all code requirements.