REFINERY VESSELS LIGHTNING PROTECTION

[duki]

I posted this in the NFPA forum and no one replied! Any takers here?

Vessels in a refinery which are tall and slim are usually not required to have lightning protection since they are constructed of metal of at least 3/16" in thickness and are electrically conductive. However, what if the vessel is covered with insulation, say 150mm in thickness, top to bottom. Normally the cladding that covers the insulation is only 14ga and not electrically continous. NFPA 780 is not specific as to whether it should be protected. Does anyone know?

 

[alehman]

I don't think there's a 'right' answer to this question. The cladding (and underlying insulation) could be damaged by a strike. If the insulation is flammable, conductive or contains water, it could explode. I would also be concerned about flashover between the cladding and tank body unless they are made electrically continuous.

Does your insurance carrier have an opinion?

 

[Kiribanda]

duki,

When we talk about lightning srikes we need to consider two issues. That is Direct strokes and Indirect strokes.

Direct strokes: By the design itself of these tall metalic vessels (columns/ reactors), they will easily conduct the lightning current to the ground. Mostly a direct stroke will leave scars/ damages at the point of strike. It is true for a floating roof tank too.

Indirect strikes: Since these vessels (columns/ reactors), are tall they are not subjected to indirect strikes due to bound charges (unless it is a floating roof tank which is having a large surface area). Only there may be damages to instrumentation/ electronic equipments installed on the vessel due to transferred potential issue/ improper grounding etc.

Therefore, in my opinion the insulating cover does not play any role in lightning strikes to these vessels.

Hope this helps

Kiri