Explosion Proof Thermocouple

[Nichyin]

Good morning everyone,

I am currently tasked to buy explosion proof thermocouples for an oil refinery. I would like to know what defines an explosion proof thermocouple, as my head engineers told me that we only need to ensure that the thermocouple we buy is sealed up at points so that no gas can enter the terminal block, and that the head needs to be ATEX approved.

However, I am sure that there are more requirements to make a thermocouple 'explosion proof'.

Thank you in advance!

NICOLAS

 

[moltenmetal]

I suspect that what you've been asked to find is a thermocouple with an explosion proof HEAD. The head contains the terminal block and/or the thermocouple transmitter. If any flammable gas seeps into the head, and somehow there is a breakdown of the laws of physics and the thermocouple manages to generate enough energy to ignite the mixture inside the head, the head's material is strong enough to contain the explosion without allowing hot gases to escape the head.

Thermocouples are intrinsically safe. Thermocouple READING devices such as transmitters, which are the only potential source of igniting energy in a thermocouple circuit, can be rendered intrinsically safe by design, or perhaps by the use of a zener barrier or the like. Or you can put the whole thing in an explosion proof head and not bother with the zener barrier. Typically, the transmitter itself comes with an explosion proof head.

This all assumes that your area classification is Class 1 Zone 0 or 1 (i.e. division 1)- normally hazardous. Most applications are NOT normally hazardous- they are typically Zone or division 2- hazardous only during an infrequent release event. In that case, explosion proof equipment is not required- nonincendive-rated instruments, without the requirement for the poured seal and clunky explosion proof box, can be used safely instead. That makes things easier to maintain, and usually cheaper.

 

[micalbrch]

I 100 % agree with Molton concerning the use of thermocouples in an intrinsically safe circuit. The only point I eventually disagree is his last paragraph. If you are in the ATEX world (and it seems you are), you'll have to install it in an intrinsically safe circuit, even for category 3 (Zone 2) applications.

 

[moltenmetal]

Micalbrch- you are of course correct. ATEX/IEC is not my native tongue and the rules are different.

 

[danw2]

Make sure you understand the paper/cert requirements, which can be just as important to some customers as the product itself.

Some vendors are more skilled at providing the accompanying certs than are others.

 

[enderlord]

The explosion proof you ask about refers to the equipment classification. There are many ways to reach the safety level you need. The equipment could be: intrinsic safe, encapsulated, oil immersed, etc.

Please see the file attached.

cheers,
vlad