An operating mode represents a specific combination of loads and boundary conditions that defines the stress-strain state of the piping system.
The initial state is always unstressed and undeformed, matching the as-built piping model. PASS/START-PROF analyzes the following operating modes:
Operating with Creep (high-temperature systems)
Cold After Relaxation (high-temperature systems)
The following parameters vary between operating modes:
Pressure and temperature values
Pipe, fluid, and insulation weights
Variable spring hanger states (locked or free)
Material properties (elastic modulus, thermal expansion coefficients)
Unidirectional restraint engagement states
Undeformed State - Zero displacements and internal forces (reference condition)
Installation After Spring Adjustment (W+P+F+Fw+H+CS+Dd) - System state after installation, insulation, cold springing, spring hanger adjustment, and final welding. Ambient temperature conditions. Friction forces initialize from the Undeformed State. Nonlinear analysis resolves unidirectional restraints and gap elements.
Operating State (W+P+F+Fw+H+T+CS+D+Dd) - System under design pressure, temperature, and fluid weight. Thermal differential: T-Tambient. Friction forces initialize from the Undeformed State. Includes equipment thermal growth displacements D. Nonlinear analysis resolves restraint engagement.
Weight in Operating Condition (W+P+F+Fw+H) - Virtual state with pressure and weight loads only. Friction forces initialize from the Undeformed State. Restraint states transfer from the Operating State. Used exclusively for sustained stress calculation per code requirements.
Operating State with Creep (W+P+F+Fw+H+χ·T+χ·D) - For high-temperature systems with creep effects. Models stress relaxation using reduced effective thermal differential χ(T-Tambient), where χ is the creep averaging factor.
Cold State (Operating Mode-T-D) - System state after cooling from Operating State. Analysis starts from operating deformed state with thermal expansion and equipment displacements removed. Ambient temperature conditions. Friction forces initialize from the Operating State. Nonlinear analysis resolves restraint engagement. Differs from installation state due to reversed friction forces.
Cold State After Relaxation (W+P+F+Fw+H-δ·T-δ·D) - For high-temperature systems with creep. Accounts for residual stresses after cooling using negative effective thermal differential -δ(T-Tambient), where δ is the relaxation factor.
After Welding Single-Use Expansion Joints - State immediately following installation weld-out of single-use expansion joints.
Test Mode (Ww+Pt+F+Fw+H+CS+Dt+Dd+Tt) - Hydraulic or pneumatic test conditions. System filled with test medium under test pressure. Spring hangers may be locked to prevent overload. Thermal differential: Tt-Tambient. Friction forces initialize from the Undeformed State.
T - Design temperature
Tt - Test temperature
P - Design pressure
Pt - Test pressure
F - Additional non-weight loads (applies to all modes, excluded from seismic calculations)
Fw - Additional weight loads (applies to all modes, included in seismic calculations)
H - Spring hanger forces
CS - Cold spring effects
W - Pipe weight + Insulation weight + Fluid weight (with code-specific load factors)
Ww - Pipe weight + Insulation weight + Test medium weight
D - Equipment displacement at operating state
Dt - Equipment displacement at test state
Dd - Support settlement
χ - Creep stress averaging factor
δ - Creep stress relaxation factor