Piping in hazardous area

[spyeh]

Why a pipeline(or a reactor) containing a fluid with its temperature much higher than AIT can exist in an electrically classified hazardous area ?
Shih-Pin Yeh

 

[MikeHalloran]

Uh, because somebody wasn't paying attention?


Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

Maybe that's why it is a classified area?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

That's what I'd say Bill.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[moltenmetal]

Fluids at temperatures above their AIT are conveyed in chemical plants safely every day of the week. Aside from the material itself being flammable, its temperature has really nothing to do with electrical area classification.

Piping and equipment with surface temperatures above the AIT of mixtures that might be released from the plant during a leakage event are frequently present in classified areas too. If you have a leak in that case, you are likely to have a fire irrespective of whether or not the electrical devices (instruments, motors etc.) are designed so that they themselves are not likely to be sources of ignition, i.e. irrespective of the area classification. It is important not to use area classification for something it is not intended. Area classification will make a simple operation like drum decanting, greatly safer- but it is of little protective use on a fired reboiler for instance (and there are plenty of those in chemical plants).

 

[spyeh]

About " ..... If you have a leak in that case, you are likely to have a fire ..... so that they themselves are not likely to be sources of ignition, i.e. irrespective of the area classification. It is important not to use area classification for something it is not intended. .....", please make deeper explanation/example for me, Thanks ! moltenmetal.

 

[waross]

Google "Auto-ignition"
Look in your copy of the NEC for the definition of classified areas.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[moltenmetal]

A material above its autoignition temperature is likely, when leaked, to mix into air at a concentration exceeding both its AIT and the lower explosive limit, hence resulting in a fire. But if the material leaks and cools below its AIT, that's even worse because the PIPE is operating above the AIT and hence behaves as if it were a spark or open flame- the PIPE itself will ignite the vapour. If you think the insulation around the pipe is vapour tight and will suppress a fire, think again...

Area classification significantly reduces the risk that electrical devices will be the source of a fire. However, in hazardous areas that already contain a non-electrical source of ignition such as hot pipe, a burner, the exhaust of an engine... area classification does nothing but give you a false sense of security. Instead, you need another means to mitigate the risk of fire and explosion: ventilation, layout, reduction in leakage points, gas detection, fire detection and suppression etc.

 

[waross]

Good points, moltenmetal.
However, for the purpose of electrical installations, the area classification is addressed in the electrical codes, NEC and CEC in the US and Canada.
The electrical area classification is concerned with preventing ignition of flammable substances by the operation or mis-operation of electrical devices.
The appropriate classification is determined by the electrical codes and then the accepted wiring methods are determined by the codes.
Auto Ignition of leaking hot fluids, but is not an electrical issue.

Fluids at temperatures above their AIT are conveyed in chemical plants safely every day of the week. Aside from the material itself being flammable, its temperature has really nothing to do with electrical area classification.

Bill
--------------------
"Why not the best?"
Jimmy Carter