3 replies to this topic

[ankur2061]

Dear All,

I came across in a company standard that flare header piping should not be buried. The explanation given was very unclear.

My personal experience is that I have seen buried sections of flare headers running to the off-plot flare stack.

Would somebody be kind enough to explain whether buried flare header piping is acceptable or not. If not, then what is the logic behind not having buried piping.

Regards,
ankur2061

[Art Montemayor]

The logic behind not having buried piping is very basic and has common sense:

Buried piping is laid in the lowest possible location and, as such, a typical low spot that will trap and accumulate liquids that have no business being there. Liquids in a flare line are a liability and a danger. A flare is not designed to burn liquids. It normally is designed to burn gases and vapors. A liquid slug into a flare line is a potential "flame-out" and, therefore, a danger.

[JoeWong]

The logic behind not having buried piping is very basic and has common sense:

Buried piping is laid in the lowest possible location and, as such, a typical low spot that will trap and accumulate liquids that have no business being there. Liquids in a flare line are a liability and a danger. A flare is not designed to burn liquids. It normally is designed to burn gases and vapors. A liquid slug into a flare line is a potential "flame-out" and, therefore, a danger.

There may be other potential issue with buried flare pipe :

"Fire rain"
Mr. Montemayor has pointed flare tip not design to burn liquid and potentially cause flare "flame-out". On the other hand, in case of the liquid is ignited, "fire rain" occur and burning liquid endanger structure supporting the flare stack.

Internal corrosion
As pointed out by Mr. Montemayor, potential generation of low pocket and promote liquid accumulation. Liquid accumulation promote internal corrosion.

External Corrosion
Buried pipe may experience higher potential of external corrosion (if the corrosion protection layer is damage). Any leak is undetectable. Another potential danger is severe leak during relief or blowdown.

Slugging flow & water hammer
During large relief, vapor with very high velocity will push the liquid accumulated in low pocket. Potential slugging flow in the flare pipe and induce severe vibration and fail the flare piping. High vapor velocity pushing liquid column will also create water hammer in the flare piping.

Unpredictable flare pressure drop
2-phase flow in flare piping will increase pressure drop a long the flare piping. This potentially affect (decrease) the PSV relief capacity (especially those low set pressure PSV).

[Technocrat]

There are also safety and environmental issues due to leakage of flammable liquid and gases through corroded pipe.