Offshore flare stacks

[helonorth]

Do any of you offshore guys (or girls) have any info as to what effect the
gasses and heat from the flare have on the helicopter? I knew the pilot
who (reportedly) hit a flare stack and crashed last week. Do not know if that had anything to do with it, but I am curious about those stacks.

[gulliBell]

Do any of you offshore guys (or girls) have any info as to what effect the
gasses and heat from the flare have on the helicopter? I knew the pilot
who (reportedly) hit a flare stack and crashed last week. Do not know if that had anything to do with it, but I am curious about those stacks.

I can assure you that any gasses or heat coming out of the flare stack have no connexion whatsoever with anyone flying into the stack!

Apart from that, standard procedures apply: avoid flying through the smoke from the flare for the comfort of the passengers and crew (and because I'm told that any sulphurous compounds in the smoke can be detrimental to the engines). Radient heat from the flare during an emergency venting is very hot, but it doesn't usually affect the operation of the helicopter.

[check]

Radient heat from the flare during an emergency venting is very hot, but it doesn't usually affect the operation of the helicopter.

Don't know where you get that from, hot air means less power and less power at the wrong time means oops at best or SH***T otherwise. Best summed up by an S61 quite a few years ago that had a heavy landing and chopped its tail off due to hot air.

[gulliBell]

Don't know where you get that from, hot air means less power and less power at the wrong time means oops at best or SH***T otherwise.


Note I said radient heat, you feel it on exposed skin much like a heat lamp, there's not much of a rise in OAT which helicopter performance is figured on. Note also I said you avoid flying in the plume, where the heat of combustion causes a significant rise in OAT which would affect your performance. So unless the flare plume is spilling over the helideck, and I've never seen that before, then my comment still stands that the flare has little affect on the helicopter.

[Langball]

I'm not a pilot, but an engineer for an offshore oil & gas company.

We don't have a 'hot flare' on our installations, but we do have some gas turbine engines that emit hot gas. Every time we modify the installation (by putting in another gas turbine) we have to do a 'Plume Study' which is essentially a computer generated 'wind tunnel test'. The worst case for us is when the wind is 'light' and obviously from a certain direction. In still air conditions the hot plume goes straight up, in strong wind the hot gas is dispersed quickly. In light conditions the hot air can 'waft' over the helideck. The outcome from the plume study is a calculated air temperature rise at the helideck, and our helicopter operator is advised accordingly (and I assume modifies his SOP to accommodate).

I'd normally expect the vent to be in the 'obstacle free sector' of the platform, so given the prevailing wind conditions you'r expect the vent to be in the lee of the helideck.

A platform venting gas during an emergency shutdown is obviously another hazard, and we have a 'Helicopter Wave Off Light' on the helideck to warn the pilots if we're about to vent gas.

[rufus.t.firefly]

What effect would a release of natural gas into the atmosphere have on
engine performance if a helicopter flew through a large amount of it without any prior warning of its presence. Does such a release effect air density and engine performance or would it dissipate that fast ??
Just something I am curious about .......anyone know the answer or encountered such ?

[skadi]

What effect would a release of natural gas into the atmosphere have on
engine performance if a helicopter flew through a large amount of it without any prior warning of its presence


Depends on the gas concentration, a large ammount of gas could be ignited or the O2-concentration is not high enough to get a good combustion in the engine.
I remember an accident in germany some time ago, where a AS 350 encountered a flameout during aerial construction, caused by the hot gases leaving that chimeney they were working at.

skadi

[Langball]

I know that diesel driven equipment on a gas installation have to have a special device that shuts off the air supply if the engine ingests gas. The engine (internal combustion) will overspeed due to the abundant supply of fuel, the normal governor won't work (it will try to adjust the diesel supply but that's not the source of the problem).

I assume a turbine engine is likely to suffer the same problem if it ingests gas, i.e uncontrolled overspeed.

[bayou06]

As a preface, I fly in the Gulf of Mexico for one of the larger Operators and fly around flare booms daily. Some of the hazards have been mentioned above;

- degradation of engine performance and/or flame out due to reduced O2 from flare (super hot air and natural gas.

- potential engine overspeed and flame out due to flying in high concentrations of natural gas.

- potential poisoning from flying through hydrogen-sulfide flare (very bad stuff)

As far as the potential to hit one on approach/departure - it's possible, but unlikely. Most are at or below helideck level, however a few larger one do rise above the deck. Regarding the EC-120 who had the fatal accident recently, my personal opinion is that he had a mechanical malfunction on approach. The EC-120 have a history of flight control and hydraulic malfunctions that are very hard to recover from coming off/on oil platforms. The pilot lived on that platform and was very familiar with the obstacles.

[vaqueroaero]

I was talking with a guy the other day who worked in the GOM for years. He was telling me one day that a co-worker of his was on a rig in a 206B. The engine was running and he was downwind of a flare stack. When he landed it was inactive but then he realised that there was now gas coming out of it and before he could do anything the TOT went off the scale and with the sudden increase in torque the aircrat did a full 360 on the pad.

[FH1100 Pilot]

Well...like everything, there's more to it than that.

There are different types of flare booms/towers. Every one I've seen (except the subsea flares) are at or *above* the heliport level.

Lit flare booms can creat an enormous amount of radiant heat that you can feel in the helicopter, even if you are not directly downwind from them and even if the actual flare outlet is high above the heliport.

Unlit flares are the problem. When the platforms "shuts-in," excess gas in the lines is vented overboard. This happens more than you might think. You can't see the gas (actually, you can if you look very, very closely and if the pressure is high enough but by then it's probably too late). If flare gas is ingested into your engine inlet, it is unregulated and, added to the ambient are it can enrichen the fuel mixture to a point where you'd have an exeedance of some sort (overspeed, overtorque or overtemp). So you have to be careful. Don't fly directly downwind of flare towers/booms.

Not every platform in the GOM has a "Flaring Gas!" light although it would be nice. Actually, it would be nice if there was *any* kind of standarization in the Gulf. The platform I lived on for nine years did have a flashing light on the flare tower. You could really only notice it if you were sitting right on the heliport.

[Gomer Pylot]

There are flare boom and then there are flare booms. High Island 264, which is a compressor station in the pipeline system, has a flare boom that has its own platform. When a slug of liquid hydrocarbon hits, and is sent to the flare and lit, it can light up the sky for many miles. That flare has melted windshields and windows of aircraft parked on the quarters platform, several hundred feet away. You do not want to fly over that flare, ever, lit or not, because it lights automatically, and cannot be stopped. I have seen flames going hundreds of feet into the air from it. Most pilots avoid flare booms instinctively, because you never know what might come from them, or when. The heat from some can definitely affect the flight of an aircraft, and the gases from unlit booms have caused exceedances on many aircraft over the years, because essentially a large amount of extra fuel, which the fuel control knows nothing about, is suddenly sent into the engine. I stay away from them, and never get close while downwind of them.

[Revolutionary]

http://members.cox.net/jasptastic/HI26407.JPG

http://members.cox.net/jasptastic/HI26409.jpg

Gomer, to illustrate your point here two pictures of the flare boom at High Island 264. One is 'at rest' and the other picture was taken during an emergency shutdown drill. It did indeed melt the windscreen of an Astar parked on the adjacent crew quarters a few years ago. Both pictures were taken from the landing pad. At that distance (no more than a couple hundred feet) the roar of the flame is deafening and the heat singes your eyebrows. Yes, it is a good idea to give flare booms a wide berth...

P.S. to give you an idea of the scale of the flame: the triangular walkway leading to the boom is about ten feet high.

[Helinut]

On offshore platforms there are various things that get emitted that can affect helicopters. The sources can be deliberate or unintended.
FLAMMABLE GASES
You can get a release of flammable gas, possibly natural gas/methane or a mix of gases like butane and propane. Depending on how much and the conditions of the release, this can end up in a variety of places. If a helicopter flies into the gas cloud from such a release, the flammable gas will add to the fuel being burned in the engine. There are two possible undesirable consequences:
the turbine will/may run up out of control; and
the gas cloud may be ignited by the engine with unhappy results for both the hele and installation.
HOT GASES & AIR
Installations have vents that from time to time vent hot air or gas. Although this may not be flammable, it can affect the helicopter because the air/gas will be hot and less dense, reducing performance at critical stages of flight.
Gas/air releases can be from intended locations or unintended ones. The timing can also be controlled or uncontrolled.
FLARES
Flares are a means of getting rid of flammable gas "safely". The intention is to vent the gas at a safe distance from the installation. These days, the gas is meant to be ignited and burn as a flare: generally flares are now only used as a safety device to cope with process upset. They are designed so as to ensure that the levels of thermal radiation from the flare incident on people or equipment are not dangerous. However, if you end up in a place never envisaged by the designer or the rate of release is greater than planned you may be in trouble.

The other issue is turbulence created by the structure, but that is rather different.

[verticalhold]

Gullibell;

Radiant heat can have an effect. I've seen OAT go from +10 up to +25 on a North Sea deck and the effect can be significant. Also on some of the older decks turbine plumes could be extremely uncomfortable.

Once landed on a new platform as P2 when I got a wiff of gas just as P1 called committed. It may be the incident Check mentioned. We lost the tail rotor and suffered a gross overtorque.

A year later one of the company investigators from the incident mentioned to me that he had had the same experience, the wind was stronger and they got away with a firm arrival.

Combined with gas, our incidendent was compounded by rapidly increasing OAT due to flare activity and turbine plumes across the deck.

Landing weights were calculated from conditions passed by the rig. Unfortunately on that day their OAT probe was out of the contaminated airflow. We were legal on the conditions passed to us, in reality with the increased OAT we should have decreased our restricted deck weight by 1000lbs.

My eyes still water from that one.

[nimby]

Do similar things happen when you're approaching the deck of a frigate slowly steaming into wind? It must have gas turbine plumes right over the deck, but then again I guess passing a building-sized object (the superstructure) through the same air will stir things up a bit?

[toolguy]

There was a very bad S61 accident in the North Sea in the early 90's when wind shifted stack heat into the landing path. It was a very hot day for the NS anyway, but it was enough for them to hit very hard then roll off.

[Telstar]

http://www.aaiu.ie/AAIUviewitem.asp?id=4571&lang=ENG&loc=1280

The lack of oxygen can cause problems too as this Pilot found out.

[bondu]

toolguy wrote,

There was a very bad S61 accident in the North Sea in the early 90's when wind shifted stack heat into the landing path. It was a very hot day for the NS anyway, but it was enough for them to hit very hard then roll off.

If this was the incident on the Brent Spar, then flare gases were not to blame, as the Spar didn't have a flare. The S61 hit the A-frame of the crane alongside the helideck, landed heavily on the deck before rolling off into the sea.

bondu

[CYHeli]

Can the helicopter exhaust (700 odd deg) ignite the gases released from the plume that were not already lit?

[Gomer Pylot]

I don't know about frigates, but the exhaust stacks from seismic boats can present challenges, probably pretty much the same thing. My technique is to approach from an angle, never from dead astern.

I doubt the helicopter engine exhaust will ignite the gas, but there is usually an electrical charge on the helicopter, as anyone who has attached an external load can testify. Discharge of this can result in a spark which can certainly ignite gas.