On this page
Key takeaways
- Onshore layout is driven by access and constructability; plot space is relatively cheap.
- Offshore layout is driven by weight, deck area and safety: escape routes, hazardous areas and congestion.
- The same process line can need very different routing, supports and material in each environment.
The problem: where do the pipes go?
Every plant connects equipment with piping, and every layout engineer is solving the same puzzle: the shortest practical routes, enough flexibility for thermal movement, and room to operate and maintain. What changes between a refinery unit and a platform deck is which constraint wins.
Onshore: the pipe rack
On a refinery or gas plant, the pipe rack is the spine of the unit. Lines run in tiers between steel or concrete frames, with process lines, utilities, flare headers and cable trays each given their own level. Large, heavy lines are usually placed near the columns to keep beam bending down, and hot lines are grouped so their expansion loops can be nested together.
Because land is comparatively available, the designer can leave clear corridors for cranes and vehicles, put valves at reachable heights, and reserve spare rack space (often 20 to 25%) for future tie-ins.
Offshore: the topside module
On a platform or FPSO the same equipment must fit on a few decks, and every kilogram adds to structure, lifting and hull cost. Piping is routed tightly around equipment, often through deck penetrations, with supports taken off the module steel.
Layout also has to protect people. Escape routes stay clear, hazardous and non-hazardous areas are separated, and flanges and small-bore connections are kept to a minimum to reduce leak points. On floating units, vessel motion and hull deflection become load cases too.
Side by side
| Factor | Onshore rack | Offshore module |
|---|---|---|
| Main driver | Access, constructability | Weight, area, safety |
| Space | Corridors, wide bays | Fixed footprint, multi-deck |
| Supports | Rack beams, sleepers | Module steel, deck penetrations |
| Extra load cases | Wind, seismic | Motion, hull deflection, blast |
| Maintenance | Mobile cranes, vehicles | Lifting beams, laydown areas |
Code reference
ASME B31.3 Process Piping: the base design code for both environments.
API RP 14E Design and installation of offshore production platform piping systems.
NORSOK L-002 Piping system layout, design and structural analysis.
What to take back to your desk
Before you route a single line, ask which constraint owns this project. If it is access, protect corridors and spare rack space. If it is weight and area, protect escape routes, minimise leak points and talk to the structural team early.
Educational content. Always design to your project specification.
