Where Cold Weather Gets In

Cold finds water. Water finds low points, dead legs and small-bore tubing, and a flare system has plenty of all three. The usual suspects:

• Pilot gas and ignition lines. Condensation gathers in the lowest section, and a partial ice plug distorts the pilot flame long before it puts it out.
• Purge lines and molecular seals. The purge protecting the tip from oxygen ingress is a small, unglamorous flow, and often the first thing trimmed to save gas.
• Instrument impulse lines. Water in a sensing line freezes and produces a reading that is confidently wrong.
• Knockout and seal drum drains. A blocked drain raises liquid level; ice in a seal drum alters the seal itself.
• Steam lines for smokeless flaring. Condensate left in a cold line arrives at the flare tip as a slug.
• Heat tracing circuits and thermostats. Often checked only when they fail, which is usually the week you need them.
• Small-bore instrument tapping points and pressure gauges. A gauge that reads zero because its tapping is plugged is worse than no gauge at all, because someone will trust it.

Most winter flare problems are not caused by extraordinary weather. They are caused by water sitting somewhere it should not be, and by instrumentation reporting the consequences without anyone tracing them back to the cause.

A freeze-up is rarely a single component failure. It is a chain: water, low point, cold, alarm, decision, trip.

Freeze Protection: Tracing, Insulation and Purge Gas

Heat tracing

Start with the circuits you already have. Confirm each trace circuit is energised, the thermostat is set sensibly, and the insulation and cladding are still intact — cladding is easily dislodged by scaffolding, and a two-metre gap in lagging is exactly where the freeze will happen. Steam traps deserve attention too: one failing closed starves the line, one failing open wastes steam and creates a burn hazard near walkways.

Reading an amp value once proves very little. Energise tracing a few days early and watch line temperature over a full night, which is when failures show up. Take the readings at the coldest point on the run, not at the panel, and record them so next year's check has a baseline to compare against.

Purge gas and hydrates

Purge gas should be dry. Check dew point at the supply, not just at the meter, and confirm the purge rate still meets the design intent — cutting it to save fuel is a false economy when the alternative is oxygen migrating into the flare header. Where hydrate inhibitor injection is fitted, check the pump, the tank heat tracing and the injection nozzle before the first cold spell. Hydrate plugs form quickly at pressure and low temperature, and clearing one is never convenient.

Remember that a purge header feeding several tips is not protected equally. The last tip on the branch sees the lowest flow and the longest residence time, which makes it the one most likely to ice up first — and the one nobody checks.

Condensate, Drains and Seal Drums

Drain the flare header low points on a schedule and note what comes out. Volume and appearance both tell you something about carryover. A drain left slightly open all summer may be a freeze point in winter, or an unwanted release path — decide which it is and set it properly.

On the knockout drum, verify that the level instrument agrees with the drain valve, and that the route to the closed drain system is clear. Where a water boot is fitted, drain it before the cold arrives rather than after a level alarm. A simple cross-check — open the drain by hand and watch the level respond — catches more problems than any amount of staring at a screen.

Seal drums are easily overlooked. Confirm the liquid level is at the correct mark and check for ice or slush around the seal and its instrumentation. If steam is used for smokeless flaring, open the line drains and warm the line through slowly before admitting full flow. Water hammer at the tip is an expensive way to learn that lesson.

A Pre-Winter Walkdown Checklist

Do the work in one organised pass, before the forecast turns. A walkdown that follows the same order every year is faster, catches more, and leaves an audit trail:

1. List every heat-traced circuit on the flare system and confirm its status, set point and insulation condition.
2. Check all pilot gas, ignition and purge tubing for low points, missing supports and crushed insulation.
3. Drain every knockout drum, seal drum, boot and header low point, and record volumes.
4. Cross-check each level and flow instrument against the physical system it is monitoring.
5. Confirm purge flow and dew point at the supply and at the flare tip end.
6. Verify the hydrate inhibitor system, including tank heat tracing and pump operation.
7. Pressure-check steam lines, open drains and confirm traps are working before full flow is required.
8. Walk the flare structure with a torch and look for cladding damage, blocked vents and standing water.
9. Confirm spares — trace thermostats, fuses, tubing fittings, insulation — are in the store, not on a delivery date.

When Something Does Freeze Anyway

Even a well-prepared system can be caught. The mistake is usually in the response, not the failure. Do not hammer a frozen line, do not apply a naked flame, and do not assume that restoring heat will immediately restore flow — a thawed plug can move as a slug and arrive somewhere it does no good at all.

Isolate where you reasonably can, warm the line slowly from the end nearest the blockage, and watch the pressure on the downstream side rather than the upstream side. Confirm alarms and instruments read sensibly again before you put the system back on full duty, and write down what froze, where, and why. That note is worth more than any generic procedure, because the next cold snap will find the same low point.

Winterising a flare is unglamorous work that competes badly with everything else on site. Done in autumn, it is a few quiet days of checking, draining and testing. Left undone, it becomes a trip at two in the morning, in weather that makes every repair take twice as long.

Photo: suju-foto / Pixabay