Learn more about PASS/START-PROF pipe stress analysis software
Accurate temperature specification for cylindrical shell elements along the column height is essential for realistic thermal expansion calculations. Proper temperature distribution ensures correct nozzle movements and reliable expansion stress analysis in connected piping systems.
Base column element temperatures on known temperatures of connected outlet lines. Consider only large-diameter nozzles that significantly affect temperature distribution. Small nozzles can be ignored.
For example, with three column nozzles (points 2, 37, 41 in the diagram below) at temperatures 40°C, 250°C, and 20°C, calculate each cylindrical shell temperature at the element center using linear interpolation between adjacent nozzles. For cylindrical shell between nodes 9-10 (T5):
Where:
T2 - Temperature of upper nearest column nozzle
T1 - Temperature of lower nearest column nozzle
x - Distance from lower nozzle to cylindrical shell center
H - Distance between upper and lower nozzles
Apply this procedure for operating, design, and other operating mode temperatures.
Calculate skirt temperature (Ts between nodes 20-21) as the average between ambient temperature and temperature at the skirt top. Use this industry-standard equation (from "Piping and Pipelines Assessment Guide" by Keith Escoe):
Ta - Ambient temperature
T - Temperature at skirt top
K - Insulation constant (K=1.0 for fully insulated, K=1.7 for firebrick insulated, K=2.7 for non-insulated)
h - Skirt height
t - Skirt wall thickness
Model columns and nozzles (points 2, 37, 38, 41) similar to vertical pressure vessels using cylindrical shell and nozzle elements.
Apply seismic, wind, snow, and ice loads to both piping systems and column shell elements.
Enter vendor-provided allowable nozzle loads in the nozzle element properties:
If loads exceed allowable values, switch to WRC 107/537/297 stress analysis:
For non-standard geometries or when WRC applicability limits are exceeded, use Finite Element Analysis with PASS/Nozzle-FEM integration:
To model column-skirt connection, add node 40 near node 20 with 1 mm offset. Insert pipe 20-21 into node 20 (skirt), add fixed anchor at node 21, reducer at node 20, and pipe 40-41 (column bottom). Connect pipe 41-43 to node 41 and insert nozzle element.
Connect pipes to column elements. Position the upper support close to the nozzle to carry vertical loads and partial horizontal piping weight. Model using rigid element (57-54) connected to column (node 57). Add internal restraint 1 mm from node 54 with three double-acting rigid restraints to exclude rotational constraints.
Model guide supports with rigid elements and internal restraints having two rigid double-acting restraints in horizontal directions.
For heavy pipes, add variable spring hangers connected to the column to support partial weight loads.
Position the first resting support on horizontal pipes at sufficient distance to accommodate thermal expansion and prevent compressive forces in vertical pipes that could cause buckling.
Set reboiler body temperature as the average between inlet and outlet nozzle temperatures.
For reboilers supported by independent structures, add two rigid elements at node 17 and place variable spring supports (or other types) at nodes 34 and 36. For reboilers with 3 or 4 lugs, add additional rigid elements and supports.
Place reboiler nozzle element at node 15 and column nozzle at node 14. Nozzles automatically model with rigid elements per nozzle element description.
For column-supported reboilers, model supporting structures using rigid elements or beam elements:
Check flange elements for leakage at nodes 401 and 27.
