A flare stack is a slender chimney with a fire at the top. It is sensitive to wind in a way that ordinary structures are not: the load that governs is often not the strongest gust but a moderate, steady wind that happens to shed vortices at the stack's own natural frequency.
Techso verifies self-supported, guyed and derrick-supported stacks under wind, vortex shedding, seismic action and thermal gradients, and delivers the foundation loads and the anchorage detailing that follow.
Configuration
- Self-supported — simplest to erect and maintain, limited by height and diameter
- Guyed — light and economical, but needs the ground area for the anchor blocks
- Derrick-supported — for tall stacks or where multiple risers are carried
- Riser arrangement, expansion and support of the flare line itself
Actions and verifications
- Wind action to EN 1991-1-4, including along-wind response
- Vortex shedding: critical wind speed, lock-in and cross-wind amplitude
- Seismic verification to EN 1998, or to the local code where required
- Thermal gradient through the stack wall and differential expansion of risers
- Local buckling of the shell and stiffener design
Fatigue and damping
Cross-wind oscillation produces cycles, and cycles produce fatigue at welded details. Where the calculated amplitude is unacceptable, the answer is either damping or a change of shape — and the choice has consequences for erection and maintenance that are worth making early.
- Fatigue assessment of welded details to EN 1993-1-9
- Helical strakes: effectiveness against the drag penalty they introduce
- Tuned mass dampers where strakes are not acceptable
- Structural damping assumptions, stated and justified
Foundations, anchorage and access
- Base plate, anchor bolt design and grout detailing
- Foundation loads and overturning, delivered in the civil engineer's format
- Guy anchor blocks and tensioning sequence, where applicable
- Ladders, rest platforms and fall protection
- Davit or maintenance arrangement for tip replacement
What you receive
- Structural calculation report, reviewable clause by clause
- General arrangement and fabrication drawings
- Foundation load schedule
- Verification of an existing stack against new duty or a new code