Alternative pipe rack expansion of the individual levels can be accomplished by adding a cantilever beam as required on the outside of the column.
The only problem with this approach is that, if not planned for, the vertical risers commonly found outside the pipe rack use a considerable amount of the space of the extension, as shown below.
Pipe rack additions are show below.
Area A shows a standard two-level pipe rack, as planned.
Because it is always possible for the pipe rack to be expanded in the future, the area over the columns must be kept free of piping and conduit.
The future expansion may include another new level (B), air cooler (C), or a series of shell and tube exchangers (D).
The preferred location of a relief header above a pipe rack is illustrated below.