In Piping analysis, one of the most significant effect is temperature difference ΔT, equal to wall temperature difference during Piping joint welding Ti (Ambient temperature) and operating mode wall temperature Top (temperature in operating mode):
ΔT=Ti-Top
Ambient Temperature - pipe wall temperature at the time of Piping welding into a solid structure. Ambient temperature is equal to:
For pipelines without single use compensators: average pipe wall (metal) temperature at the moment of welding the final joint to make a connected structure.
For pipelines with single use compensators: average pipe wall (metal) temperature prior to Piping pre-heating.
Ambient temperature is not usually known in advance, so a minimum value ensuring an adequate safety margin must be used based on the region's atmospheric data. It should be noted that welding cannot be done at atmospheric temperature below a certain degree.
Ambient temperature should be calculated as:
Ti = max(Tconstr, Tatm),
where
Tconstr - minimum atmospheric temperature value, at which open-air construction and welding can be done according to standards and manuals. Tconstr usually depends on steel type and wall thickness, and falls between -20ºC and 0ºC.
If special shelters or pre-heating can be used during welding, it can be done at any atmospheric temperature. In this case, Ti = Tatm.
Tatm - atmospheric temperature at the moment of Piping welding.
For buried pipelines with PUR insulation, Tatm is usually set as 0-10°С. It is assumed that the final joint is welded when the trench is backfilled, so Piping wall temperature cannot be negative.
The project must have a clause that Piping welding is not allowed at atmospheric temperature below Ti
Operation temperature is the average temperature of pipe walls (material) in operating mode, Top. It is often set as equal to product design temperature.
If the product temperature is closed to maximum atmospheric temperature (cold Piping), taking into account maximum atmospheric temperature and possible pipe wall heating due to direct sunlight is recommended for determining operation temperature; i.e. the greater of two values:
Top=max(Тproduct,Тcross-section),
where
Тproduct - product temperature. Using temperature that is not exceed for more than 30 days in a year is recommended. For example, 150ºC for heating networks.
Тcross-section - average pipe cross-section temperature in warm season taking into account the wall heating from atmospheric and sun rays.
Tests are usually performed to check joint seals; i.e., to check installation quality. If water is used for testing (hydraulic testing), atmospheric temperature should be positive to prevent the water from freezing. Usually test temperature of +20°С is used.
1. SNIP 2.01.07-85* - Loads and effects (section 8.1-8.7)
2. SNIP 2.01.01-82 - Structural climatology and geophysics (outdated)
3. SNIP 23.01.99* - Structurally climatology (replaced SNIP 2.01.01-82)
4. SNIP II-3-79* - Thermal engineering, appendix 7 (outdated)