FLARE PIPING

Flare, a system that meticulously disposes of a plant's waste gases, is a testament to the precision in industrial operations. Flare stacks, towering structures, are designed with utmost care to route the gas to the atmosphere, usually with a flare tip, ensuring the safety and efficiency of the process.

Flare headers are the lines in units that receive relief valve discharges, vents, etc., and route the gas to a flare knock-out drum, which separates any liquid that may have condensed in the header.

Waste gas from the knock-out drum is then routed to the flare stack. Knock-out drums are located near the flare stack to keep the line from the drum to the stack as short as possible. •

Flare headers must self-drain from the origin to the Unit knock-out drum and then self-drain from the Unit knock-out drum to the Flare knock-out drum. In some cases, the flare is located at a higher elevation; in this case, the flare line will slope to the unit knock-out drum.

Lines from relief valves to the flare header must also be routed so as to be self­draining into the top of the header (See Figure-1 ). This means that relief valves will be located higher than the flare header. Therefore, the unit flare header is usually one of the highest lines in the pipe rack.

In some cases, it is impossible or impractical to keep relief valve outlets self-draining to the flare header. However, a liquid pocket cannot be allowed to cause uncalculated back pressure on the relief valve. A manual drain valve shall be installed when the relief valve outlet is lower than the flare header; see Figure 2.

For relief valves vented to the atmosphere, the tailpipe is to terminate a minimum of 3000 mm above any platform within a 15 m radius.

Relief valves must be accessible from a platform. Always mount relief valves with ·the spring vertical except for small liquid thermal relief valves, which may be installed with the spring horizontal. Valves in flare lines shall be installed with the stem horizontal or downward.

A long-standing myth among piping designers calls for a 45° bevel on the relief valve tail pipe discharging to the atmosphere. The myth suggests that beveling will direct the outlet velocity away from a platform or building. However, the truth is that a square cut end, as shown in Figure 3, will direct the discharge upward, away from the platform, and at a lower cost. The myth's real flaw becomes apparent when observing the actual installation where bevels have been cut, which, in effect, directs the velocity toward operating platforms. This is due to the improper orientation of the bevel. The square cut eliminates all orientation problems, providing a clear and safe solution.

 In conclusion, (flare piping) is an essential system in the oil and gas industry, ensuring the safe and efficient disposal of waste gases. By understanding and implementing proper design and maintenance practices for (flare stacks), (flare headers), and (knock-out drums), we can enhance safety, minimize environmental impact, and maintain operational integrity.

Reference: FW Piping Lesson