As we stated earlier the sequence of piping drawing production is P&ID, Piping Arrangements and then Fabrication Isometrics. Isos are isometric drawings of individual pipes taken from the arrangement drawings. The intention here is to transmit the required information to the pipe fabricator and to eliminate any confusion which may arise from interpretation of the arrangements (some arrangements can be pretty confusing).
- Usually the rule is one line per iso, however if that line is extensive, making the iso too crowded, split it up into as many isos as needed.
- Isos are drawn with the plant north arrow pointing to the top left or right of the drawing paper, depending on the clients standard preference.
- The iso may contain several "spool pieces" because of flanges or other breaks. The fab shop will make these individually and ship them to the field with individual mark numbers so that they can be erected in the correct connectivity. Similarly other flanged components such as valves, bolts and gaskets are shipped to the field by the supplier and assembled to the fabricated piping.
- Spool pieces must be shipped in a container, thus the maximum size of a spool piece must fit into a shipping container measuring 40'x8'x8' (12m x 2.5m x 2.5m)
- Dimensions to equipment and/or columns and a reference co-ordinate should be indicated on the iso. This is required for erection in the field.
