Industrial Electrical-Containment walls around a tank

[DJB]

To the newsgroup:

Has anyone come across this before? At the local refinery where I do some
work for they have storage tanks with containment walls just in case there
is a leak out of the tank. They could be concrete or mounds of dirt and
stone. These were installed long ago. In some cases they have conduits going
through the sides of the containment walls for electrical power or
instrument signals.They have seals on the conduits for going from one area
classification to another area classification to meet the explosion proof
requirements. Is there anything out there that could prevent liquid seeping
through the conduits going through the containment walls in case of a tank
leak? Would the explosion seals be suffient? Any feedback would be greatly
appreciated.

Thanks in advance,

Dave

 

[Cameron Dorrough]

To the newsgroup:

Has anyone come across this before? At the local refinery where I do some
work for they have storage tanks with containment walls just in case there
is a leak out of the tank. They could be concrete or mounds of dirt and
stone. These were installed long ago. In some cases they have conduits going
through the sides of the containment walls for electrical power or
instrument signals.They have seals on the conduits for going from one area
classification to another area classification to meet the explosion proof
requirements. Is there anything out there that could prevent liquid seeping
through the conduits going through the containment walls in case of a tank
leak? Would the explosion seals be suffient? Any feedback would be greatly
appreciated.

There are electrical standards that deal specifically with the electrical
equipment installed in "hazardous areas" as they are called (the IEC 60xxxx
series comes to mind, but I don't know what is applicable in your country.)

To answer your question, the bund wall is there to contain a spill (ie. in
an emergency) and is not really designed to contain liquid all the time, so
a bit of possible seepage is not usually a problem.

Any conduits going through the bund wall have to be petrochemical-resistant
and liquid-tight themselves (some plastics are out) and be sealed using
'Y'-seals - tee-shaped sections of the conduit filled with an epoxy putty
filler.

In my experience, electricians usually leave the epoxy out of the 'Y'-seal
to make it easier to pull more cores through later on - making the
installation an bit dodgy to say the least - but a good inspector should
pick this up.

The problem is actually not the liquid only - it's the flammable vapours.
Even with the barrier, it is possible to get vapours travelling up the
interstices of the cable and causing explosions in supposedly safe areas
(like switchrooms).

I hope this helps.

Cameron

 

[Maintech]

Good one Cameron! I just recently went through this with a couple of fuel
tanks. The first one wired by the contractor on site at the time, knowing
that we where going to install another one later, so they left the conduit
unsealed. After the second tank was installed, my maintenance manager did
the wiring and used the seal as a conduit body instead and never sealed the
conduit at either end. He was confused when I did up a "work order" to
correct this potential hazard. After the maintenance manager talked to a
Yard foreman the foreman called in a contractor to correct it. My saying is
" Do it right the first time", If you don't know what you're doing, then
leave it to me.

 

[Cameron Dorrough]

Good one Cameron! I just recently went through this with a couple of fuel
tanks. The first one wired by the contractor on site at the time, knowing
that we where going to install another one later, so they left the conduit
unsealed. After the second tank was installed, my maintenance manager did
the wiring and used the seal as a conduit body instead and never sealed the
conduit at either end. He was confused when I did up a "work order" to
correct this potential hazard. After the maintenance manager talked to a
Yard foreman the foreman called in a contractor to correct it. My saying is
" Do it right the first time", If you don't know what you're doing, then
leave it to me.

Personally, I'm not real keen on the typical G.I.W.P./'Y'-seal system you
guys use over there for just that reason. That's a job for a plumber - not
an electrician! ;-)

Most (all new) installations over here (and indeed, a majority of places
outside the USA) use steel-wire armoured cabling and barrier glands instead
of the rigid metal conduit system you put up with.

Apart from being flexible, SWA cabling is quicker to install and can be
glanded off correctly the first time around. If you need to run another
cable later on, pulling the cables through open-ended HDPVC conduit, sealed
each end with foam filler to keep the rats out, makes the task far easier
than having to remove the epoxy putty from a 'Y'-seal to just 'cause you're
short a few cores..

Not many people realise that with conduits starting in a "hazardous area",
the "hazardous area" actually exists for the *full length of the conduit* -
right up to the barrier - especially if the conduit is underground (and you
can't see where it goes). I have seen quite a few safe-area junction boxes
blow up in my time, scaring the crap out of the operators nearby... In the
petrochem business, a small spark makes a big bang!

Cameron