I have a question about starting a fire on a natural gas pipeline.
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I would like to ask the experts, when performing hot work such as cutting and welding on natural gas pipelines, to what extent do the combustible gases in the pipelines need to be replaced with nitrogen? For example, the combustible gas content must be less than 1%?
Less than 0.5%. Refer to AQ3022-2008 "Safety Code for Hot Work in Chemical Production Units".
It should be at least less than 10% of the LEL of methane. I remember that the LEL of CH4 seems to be 5%.
Regarding the issue of combustible gas content, I personally think there are two indicators: Percent content of LEL and organic matter. I think both indicators are 0 which is the safest, but in general it is impossible to achieve. Some units must require the LEL to be lower than 5%. If the LEL is higher than 5% and lower than 20%, it must pass a risk analysis and be approved by the general manager. In addition, the effective isolation of pipelines and the reliability of detection instruments are also keys to safe operations, and fire prevention preparations and emergency plans are also necessary. In short, this type of high-risk operation requires sufficient demonstration and strict implementation of the formulated fire plan in order to be foolproof.