Flare Header Routing: Onshore Plant vs Offshore Platform

The job of a flare header

Relief valves, blowdown valves and depressurising systems all discharge into the flare system. The header collects these flows and takes them to a knock-out (KO) drum, which removes liquid, and then to the flare tip, where the gas is burned.

Common layout rules

• Continuous slope towards the KO drum. A slope of around 1:500 is common, but follow the project specification. Pockets collect liquid that can be pushed along as a slug.
• Laterals enter from the top of the header, often at 45° in the direction of flow, so liquid drains into the header and relief flow merges smoothly.
• No pockets in relief valve outlets. Where a relief valve sits below the header, it may need a drain or a different arrangement.
• Large expansion range: blowdown gas can be very cold while relief from a hot column can be hot. Material (often low-temperature carbon steel or stainless steel) and flexibility must cover both.
• Acoustic-induced vibration (AIV): high flow rates through relief and blowdown valves create high acoustic energy that can cause fatigue in the downstream piping. Small-bore connections and branch welds near the source are at risk. Screening methods such as those in Energy Institute guidance are used to identify lines that need thicker walls or full-encirclement branch reinforcement.

Onshore

• The flare stack is placed at a distance from the process area to limit thermal radiation at grade, so the header is often long.
• The header runs on the rack, usually on the top tier, then along a dedicated pipe track to the KO drum and stack.
• A long header has a large drop in elevation if sloped continuously, so the KO drum and the rack elevations are planned together.
• The long run means large thermal movements, so anchors and loops are needed.

Offshore

• The flare is mounted on a flare boom or a tower extending away from the platform, or at one end of an FPSO.
• The header is shorter but runs through congested modules, so keeping a continuous slope is difficult.
• The KO drum is located close to the boom base, and the header to the tip runs up the boom structure, which moves and vibrates in wind.
• Weight and radiation limit header size and location. Cold flaring and venting cases add low-temperature requirements.

Item	Onshore	Offshore
Header length	Long, to a remote stack	Shorter, through modules to a boom
Main layout challenge	Elevation for continuous slope	Congestion and slope
Support	Rack and pipe track	Module steel and boom structure
Special loads	Thermal growth over long runs	Motion, boom movement, AIV

What to take back to your desk

Mark the flare header and its laterals early in the model with their slopes, and protect that space. Flare headers are big, sloped and inflexible in routing, and they lose every clash fight late in the project.