Plant design software lays out a plant's pipes, vessels and steel structures in 3D. The plant is built from this layout, and later maintained from it. A refinery has a very large amount of pipe, so nobody can plan it on paper.
The layout starts from the sizes that chemical process simulation gives. The designer places each tank and pump, and then routes the pipes between them. Each pipe carries data: what it carries, its diameter, its material and its pressure rating. A beam, a valve and a pipe are all 3D objects. So the software can find a clash, a place where two objects occupy the same space.
Consider a fertiliser plant in Odisha where a designer runs a pipe along a pipe rack, the steel frame that carries many pipes. She runs the clash check. The software shows that a 300 mm pipe passes through a steel beam. She moves the pipe 400 mm higher, and the clash is gone. Finding this on site would have cost days of cutting and welding. The pipe sizes themselves come from a piping and instrumentation diagram (P&ID), which shows every pipe, valve and instrument in a plant as symbols and lines, without the 3D positions. From the finished model, the software then produces the drawings that fabricators use to make each pipe, and the list of every pipe, valve and fitting to buy.
Different companies do different parts of this work. An engineering, procurement and construction (EPC) company designs the plant and builds it for the owner. When the plant is finished, the EPC company hands the 3D model to the owner. The owner's maintenance team then keeps using the model for years, for instance to plan how to replace a pump without cutting other pipes.
The layout is passed to other software. A plant digital twin shows the plant and its live data on the same 3D model. Engineering data integration checks that the data in the model agrees with other records, such as the equipment list. Construction management software uses the drawings to plan and track the building work.
Plant design software is close to BIM software, which does the same job for buildings. For roads, bridges and similar works, civil infrastructure design software is used.