A Piping Lead Discipline engineer colleague of mine recently explained to me the purpose of the Piping line diagrams (page 106). As we know, the P&IDs are not geographical hence do not give any idea of the length of lines. The Line Diagram does. It therefore allows to measure the length of lines and to produce the first piping material take-off. In addition, the line diagram shows the number of lines on each pipeway/piperack. It will therefore allow to determine the width of the pipe ways, width and number of levels of pipe-racks etc. Such width is not directly shown on the line diagram as the latter is, after all, a "diagram" and not a "drawing" hence it is not to scale. It does not take into account the space taken by each line (depending on its diameter) and their spacing. This will have to be determined in a second step, by making typical sections. Once this will have been done the footprints of pipe ways and pipe-racks whill be known, which have to be fed into the Plot Plan. Another purpose of the line diagram is to identify the density of lines in the various areas. It will then be used to split the piping routing study work in different areas, of same work volume, to each of which will be assigned a different lead engineer producing the piping studies (page 107). Lastly, the line diagram allows piping to identify the order of the connections on a header, such as a flare header, and to provide such information to Process, in the form of comments on P&IDs. With such information, Process can size the header with properly positioned diameter increases throughout its route.
