# Piping Operating Modes

The piping mode is a design combination of loads and effects determining the stressed-deformed Piping mode. Initial mode is always not stressed and not deformed (corresponding to the piping model). The following modes are possible:

The following varies in different operating modes:

Non-Deformed State - the displacements and internal forces are zero

(W+P+F+Fw+H+CS+Dd) - Mode after Piping installation, thermal insulation installation (or before it), completing cold springing (pre-stretching), adjusting all springs and welding of all joints. Temperature difference is zero. Friction forces direction shifts from Non-Deformed State. The state of single-directional restraints and restraints with gaps are calculated using nonlinear analysis.

Operation State (W+P+F+Fw+H+T+CS+D+Dd) - piping is filled with the product (W) and heated to the temperature T. Temperature difference is T-Tambient. Friction forces direction shifts from Non-Deformed State. Added displacements due to the heating of connected equipment D. The state of single-directional restraints and restraints with gaps are calculated using nonlinear analysis.

Weight in Operation State (W+P+F+Fw+H) - virtual mode, when only pressure and weight loads are applied. Friction forces direction shifts from Non-Deformed State. The state of single-directional restraints and restraints with gaps are taken from Operation mode (for example, if resting support lift off in Operation State then it will be excluded in Weight in Operating State and vice versa). This is not real operating mode and used only for sustained stress calculation.

Operation State with Creep (W+P+F+Fw+H+χ·T+χ·D) - for  high-temperature piping with creep. Thermal elastic deformation eventually becomes residual (plastic). As a result, resistance in operation mode spontaneously decreases. Analysis in this case is done for a fictitious temperature difference χ(T-Tambient), which depends on the creep stress averaging factor χ.

Cold State (Operation Mode-T-D) - Piping state after cooling down from Operation State. The analysis is performed from initial deformed state (Operation State), thermal expansion and displacement are removed. Piping temperature is equal to Ambient temperature Tambient and temperature difference is 0. Friction forces direction shifts from Operation State. The state of single-directional restraints and restraints with gaps are calculated using nonlinear analysis. This mode is different from Installation After Spring Adjustment State, because the friction forces usually has the opposite direction (see friction factor)

Cold State After Relaxation (W+P+F+Fw+H-δ·T-δ·D) - for high-temperature piping with creep. Thermal elastic deformation eventually becomes residual (plastic) and resistance in operating mode spontaneously decreases. After cooling, stress is not decreased to 0, but rather becomes negative. For example, if a high-temperature Piping is compressed in operating mode, it will be stretched after cooling. Analysis in this case is done for a fictitious negative temperature difference -δ(T-Tambient), which depends on the relaxation factor δ.

mode immediately after welding single use compensators.

Test Mode (Ww+Pt+F+Fw+H+CS+Dt+Dd+Tt) - hydraulic or air test mode. Piping is filled with water or gas (Ww) under test pressure Pt. To avoid overload, variable spring supports may be locked (rigid) in this mode. Temperature difference is Tt-Tambient. Friction forces direction shifts from Non-Deformed State

### Legend

T - design temperature

Tt - test temperature

P - design pressure

Pt - test pressure

F - additional non-weight loads. Considered in all operating modes. Not used for seismic load value calculation

Fw - additional weight loads. Considered in all operating modes. Used for seismic load value calculation (Fw+W)

H - variable or constant spring hanger force

CS - cold spring

W - pipe weight*1.1+Insulation weight*1.2+fluid weight*1.0 or pipe weight+Insulation weight+fluid weight depending on code requirement

Ww - pipe weight+Insulation weight+(water or zero weight at test state)

D - support displacement at operation state

Dt - support displacement at test state

Dd - Support settlement

χ - creep stress averaging factor

δ - creep stress relaxation factor