Line list

The line list is the piping system's index and database in one. Each line the P&IDs show gets a row, and the row accumulates the line's defining data — the conditions that size it, the class that sets its materials, the from–to that locates it in the plant's topology, the flags that drive stress analysis, heat tracing, insulation and test packs. Process and piping engineering maintain it jointly; stress, materials, testing and commissioning all consume it.

Its value is exactly its danger: the same facts exist on the P&ID, in the model and on the list, and the three are maintained by different hands on different rhythms. A line resized on the P&ID but not the list, or reclassed on the list but not the model, is a defect with no owner until a reviewer or a hydrotest finds it. Mature projects define which document masters which field — and audit the reconciliation, because the definition alone has never once been enough.