Lines generally require four to seven identifying elements. Symbology depends on the facility and organization involved. These elements are as follows:
• Plant number
• Service. Also called a “line identification letter” (i.e., process, instrument air, caustic)
• Line number. Often (and best) a separate unbroken series restarting with each service designation (critical for large jobs to keep number length reasonable)
• Nominal line size
• Piping classification. Service classification, service, etc. Specifies pipe, valves and fittings
• Heat tracing
See Standard Drawing ICM-EF-824A. For major processing plants in which many additions and changes are anticipated during the design phase and later, sequential line numbering that follows process and utility flow is recommended.
To minimize line numbers and better indicate process relationships, line numbers at processing facilities usually run unchanged from one piece of equipment to the next, including branches to multiple or similar pieces of equipment such as a pump and its spare. Also, the number is not changed for a change in pressure or materials.
COPI and some producing organizations change line numbers when the pressure classification (piping classification) changes, on branches to multiple or similar equipment, and when a materials change is required. Their requirements differ from major processing plants. They have many fewer piping classifications and much larger pressure changes that need to be clearly indicated. COPI assigns a different series of sequential numbers for each service, and has a very organized numbering procedure.
In larger plants (particularly those constructed by large contractors) it is necessary to keep track of assigned line numbers using line schedules. Otherwise, accidental reuse of the same number would surely occur. In addition, line schedules are required by some governmental agencies for permitting.
A line schedule often becomes a valuable control document summarizing all piping design criteria, including the following:
• Design/process information critical to line design and specification (service flow, pressures, temperatures, viscosity, density, pour point, etc.)
• Resulting design information (pipe size, piping classification, insulation, heat tracing specifications, etc.)
• Line connection points (to/from)