After the bent spacing, rack width, and number of levels are established, the elevation of the levels must be set.
The plant layout designer must know the minimum clearances to set the elevations. Plant roads, type of mobile equipment, and equipment located beneath the pipe rack can influence the pipe rack elevation.
Road clearance shall be 7M / 9M minimum for main road and 6M /5M for secondary road.
Usually, space is allowed below the pipe rack for equipment, with a minimum clearance of 10 ft (3,050 mm). (4.5 M in Jacobs PDB).
For Offsites, clearance beneath pipe rack shall be 2.2M minimum both in longitudinal and transverse directions.
The next factor to consider is the dimension between the bottom of a line in the rack and the bottom of a branch as it leaves the rack.
For example, if a review of the largest lines in the entire pipe rack indicates that there are two or three large-diameter lines (e.g., 18, 20, or 24 in) and the remaining lines are 12 in, the exit level above and below the rack can be 3 ft (915 mm).
The dimension from the end of a 900 butt-weld elbow to the centerline of a 12- in line is 18 in (457 mm).
Following figure show illustrates how to handle the large-diameter lines by using a 45° elbow or trimming an elbow to a more shallow angle.
If the instrument and electrical conduit are installed on a separate level, the estimated dimensions of each tray must be obtained from the instrument and electrical engineers to ensure that adequate space is provided.
The design of the pipe rack is now complete with the exception of installing equipment over the rack.