Rack loading is provided to Civil Engineering Department for economic designing of the pipe rack. Providing pipe rack loading is a very difficult task for a stress engineer as most of the organizations does not have any guidelines.
Normally Pipe rack loads are transferred in 3 stages:
- Initial rack loading for rack foundation design (before piling): Project has just started and very less data is available. Piping design places the lines over the rack based on preliminary P&ID. Rack loads are provided mostly based on assumption/experience. Conservative loads are to be provided.
- Rack loading for member sizing (after 30% model review): Most of the data has started arriving. Loads to be provided based on actual analysis.
- Rack loading for final member checking (after 60% model review): All vendors are decided. Line size and locations are finalized. All critical lines are fixed. Loads are provided for checking designed members again. Loads to be provided based on Software analysis.
Few points to keep in mind while providing Rack loading:
- Operating, Water filled and Occasional loads for big size lines (>16 inch NPS) to be provided separately. For guides and anchors loads with and without friction should be provided.
- For Flare line 1/3rd water filled weight can be considered.
- Proper directions to be marked.
- After a long run don’t provide guide in the immediate first possible location after bend.
- Consider concentrated loads of inline valves, flanges, equipments etc.
- Sometimes large equipments are placed over the pipe racks (Air Fin Fan Cooler, Heat Exchangers etc). So take operating weight of equipments from mechanical group.
- Cable tray loads are to be taken from electrical/instrumentation group. (In absence of data a uniformly distributed load of 1.0 KPa for single level and 1.9 KPa for double level of cable trays can be considered)
- Include the forces of PSV reactions if applicable.
In absence of data following guidelines can be used as preliminary piping loads:
- A uniformly distributed load of 1.9KPa for piping, product and insulation can be considered for line size (for each line)
- For line size larger than 12 inch nominal diameter actual concentrated load including the weight of piping, product, valves, fittings and insulation shall be used.
Load types can be divided as follows :
- Sustain Load (Dead Load) : Weight of piping, valve and Insulation.
- Thermal Load : Load by thermal expansion of piping on guides, limit stops and anchors & Reaction force by internal pressure of expansion bellows
- Dynamic Load : Load by vibration of piping & by wind and earthquake
- Sustained Load (Live Load) : Liquid load for hydrostatic pressure test and Live load (L) on access platforms and walkways and on equipment platforms should be considered, as applicable.
- Wind Load (W): Transverse wind load on structural members, piping, electrical trays, equipment, platforms, and ladders should be determined in accordance with project approved design code.