Installation, Design and Test Temperature

Temperature Difference

Temperature difference ΔT is one of the most significant factors in piping stress analysis. It represents the difference between installation temperature T_i (Ambient Temperature) and operating temperature T_op (Design Temperature):

ΔT = T_i - T_op

Ambient Temperature

Ambient Temperature - pipe wall temperature during final welding when the piping becomes a continuous structure. Ambient temperature equals:

• For pipelines without pre-loaded expansion joints: average pipe wall temperature during final closure weld installation.

• For pipelines with pre-loaded expansion joints: average pipe wall temperature before pre-loading.

Ambient temperature is typically unknown during design, so conservative minimum values based on regional climate data should be used. Welding cannot be performed below certain atmospheric temperature limits.

Calculate ambient temperature as:

T_i = max(T_constr, T_atm)

where

T_constr - minimum atmospheric temperature for outdoor construction and welding according to standards. T_constr depends on steel type and wall thickness, typically between -20°C and 0°C.

When using shelters or pre-heating during welding, work can proceed at any atmospheric temperature. In this case, T_i = T_atm.

T_atm - actual atmospheric temperature during piping welding.

For buried PUR-insulated pipelines, T_atm is typically set to 0-10°C, assuming final welding occurs during backfilling when pipe wall temperature cannot be negative.

Project specifications must prohibit welding at atmospheric temperatures below T_i.

Design Temperature

Design temperature T_op is the average pipe wall temperature during normal operation. Typically equals the design fluid temperature.

For cold service piping where fluid temperature approaches maximum ambient temperature, use the higher of these values:

T_op = max(T_product, T_{cross-section})

where

• T_product - design fluid temperature. Use temperature not exceeded for more than 30 days annually. For example, 150°C for district heating systems.

• T_{cross-section} - average pipe cross-section temperature in warm conditions, including solar heating effects.

Test Temperature

Pressure tests verify joint integrity and installation quality. For hydrotesting, atmospheric temperature must be above freezing to prevent water solidification. Typical test temperature is +20°C.

References

1. SNiP 2.01.07-85* - Loads and Effects (sections 8.1-8.7)

2. SNiP 2.01.01-82 - Structural Climatology and Geophysics (obsolete)

3. SNiP 23.01.99* - Structural Climatology (replaces SNiP 2.01.01-82)

4. SNiP II-3-79* - Thermal Engineering, Appendix 7 (obsolete)