Flame Arrestors on Natural Gas and Oxygen Vent Lines

Pavan Kumar · Apr 28, 2025

Hi All,

I have been tasked to size and specify End of the Line Flame Arrestors (FAs) to be installed on the vent line for Natural Gas and Oxygen pipe lines. The idea is to prevent an external flame from propagating into the Pipe line when it is purged with N2 gas. The purge gas is vented to the atmosphere through the Flame Arrestor. I have used software like the one provided by Protectoseal to size in-line and end of line Flame arrestors installed upstream of Pipe Away and Conservation Vents installed on atmospheric storage tanks. The size is selected by calculating the tank pressure during the venting event by adding the pressure drop in the vent line, FA and make sure that this pressure does not exceed the tank MAWP. Now what methodology do I apply for these NG and Oxygen Venting lines for sizing /selection of the end of line FAs. Any reference or guidance will be of great help to me.

Thanks and Regards,
Pavan Kumar

georgeverghese · Apr 29, 2025

Why do you need a FA for O2 vent lines ? Its not flammable.

Pavan Kumar · Apr 29, 2025

georgeverghese said:
Why do you need a FA for O2 vent lines ? Its not flammable.

Hi George,

It is said that Oxygen can heat up the piping due to high velocity and can cause the metal to burn. Particle impingement can cause this heating as well.
I recently received training to this effect.

Thanks and Regards,
Pavan Kumar

georgeverghese · Apr 29, 2025

But in this case, the oxidant is already within the pipe, so I dont see what the FA will do to arrest the combustion. Besides, combustion can occur anywhere in the pipe where static could generate a spark.

Pavan Kumar · Apr 29, 2025

georgeverghese said:
But in this case, the oxidant is already within the pipe, so I dont see what the FA will do to arrest the combustion. Besides, combustion can occur anywhere in the pipe where static could generate a spark.

Agree. It makes sense to me.

Pavan

pierreick · Apr 30, 2025

https://paradoxintellectual.com/uploads/3/5/0/4/35044814/flame_arresters_in_piping_systems_api_2028.pdf

Pierre

horacio Torres · May 30, 2025

Pavan Kumar said:
Hi George,

It is said that Oxygen can heat up the piping due to high velocity and can cause the metal to burn. Particle impingement can cause this heating as well.
I recently received training to this effect.

Thanks and Regards,
Pavan Kumar

It is extremely challenging to achieve that velocity, and a flame arrestor is not a viable safety device in this case.

Horacio

shvet · Jun 2, 2025

horacio Torres said:
It is extremely challenging to achieve that velocity

The 4 or 30 m/s limit is not challenging to achieve during an uncontrolled purge or relief.

EIGA's std. 13/12

4.4 Velocity and gas pressure criteria
4.4.1 General
...
The equation of the impingement velocity curve in Figure 2 is defined as follows:
– If 0.3 MPa abs (45 psia) < P < 1.5 MPa (225 psia) then V(m/s) = 30 m/s (100 ft/s)
– If 1.5 MPa (225 psia) < P <10 MPa (1500 psia) then P * V = 45 MPa * m/s (22 500 psia * ft/s)
– If 10 MPa (1500 psia) < P < 20 MPa (3000 psia) then V(m/s) = 4.5 m/s (15 ft/s)
...

The equation of the non-impingement velocity curve is defined as follows:
– If 0.3 MPa abs (45 psia) < P < 1.5 MPa (225 psia) then V(m/s) = 60 m/s (200 ft/s)
– If 1.5 MPa (225 psia) < P <10 MPa (1500 psia) then P * V = 80 MPa * m/s (40 000 psia * ft/s)
– If 10 MPa (1500 psia) < P < 20 MPa (3000 psia) then V(m/s) = 8 m/s (26.6 ft/s)

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Flame Arrestors on Natural Gas and Oxygen Vent Lines

Pavan Kumar

Chemical

georgeverghese

Chemical

Pavan Kumar

Chemical

georgeverghese

Chemical

Pavan Kumar

Chemical

pierreick

Chemical

horacio Torres

Chemical

shvet

Petroleum

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