Welding fittings together

[kwired]

I suppose you could thread the fittings together and then just tack them.... it's not like you have to weld the whole thing up so it doesn't leak like it was some sorta gas pipe.

I'm curious how you'd weld in an atmosphere that was so explosive that it prompted you to weld your fittings together to prevent them from arcing on a fault.:huh:

At initial construction the explosive atmosphere is not there yet. Afterwords there may be ways with positive ventilation and strict procedures of how to do so, can't say I know for sure but see it as possible.

Have seen welding done on live gas pipe, they light the gas before welding, when welding a tap to a live line or other similar operation. When the fire goes out it means the leaking gas has been sealed off and there is no more gas to feed the fire.

 

[rbalex]

Section 500.8(E) outlines the requirements for threaded installations in Classified locations.

Welding various joints, besides the general prohibition in 300.18, has the potential of increasing the explosion hazard. Threaded joints provide relief from "pressure piling."

 

[mikeames]

I am curious I thought explosion proof installations were to prevent the atmosphear from getting into the system not the other way around? What would "explode" in a properly wired, properly sealed installation? I have also seen that ilustration dealing with cooling gases through threads but I figured that was releated to any arching that might take place in switch, breaker etc....

 

[kwired]

I am curious I thought explosion proof installations were to prevent the atmosphear from getting into the system not the other way around? What would "explode" in a properly wired, properly sealed installation? I have also seen that ilustration dealing with cooling gases through threads but I figured that was releated to any arching that might take place in switch, breaker etc....

You can seal them all you want there is still a chance something can find a way in. It is easier to design it to be able to contain an explosion instead of trying to prevent one where you know there will be arcing. The arcing normally does happen at switches, breakers, etc. if the gases are present they will be subject to ignition. Another method could be non explosive positive pressure inside the raceways and enclosures assuring the gases on the outside do not get inside.

 

[rbalex]

From Section 500.2 Definitions:

Explosionproof Apparatus. Apparatus enclosed in a case
that is capable of withstanding an explosion of a specified
gas or vapor that may occur within it and of preventing the
ignition of a specified gas or vapor surrounding the enclosure
by sparks, flashes, or explosion of the gas or vapor
within, and that operates at such an external temperature
that a surrounding flammable atmosphere will not be ignited
thereby.

Also take a look at Section 500.8 for various Protection Techniques that are recognized in Classified locations. Note explosionproof is acceptable in Class I but not Class II or III. The philosophies of protecting in each Class are different. Some, like pressurizing, are pretty universal but it can become an extremely complicated system for large applications.

 

[mikeames]

You can seal them all you want there is still a chance something can find a way in.

I would respectfully disagree as gas pipe is welded and throughly tested for leaks. I would also argue, although I may be wrong in this case that preventing an explosion is easier than containing one especially when you dont know the magnitude.

I am most likely wrong I don't knwo this well, but it would seem that welding although not perfect would be no worse than other methods as far as safety and system integrity. It would seem that if threads were so vital to relieving pressure that an explosion proof pressure relief valve woudl be specifically designed for this rather than a back handed approach of relying on unsealed threads.

Also if soemthing does get in to cause an internal explosion then isnt it game over anyway??? If it got in before the internal explosion when wont hot gases get out during or after the explosion.

I have been around long enough to know that what I think makes sense may be wrong and what may make sense and is correct is not always how its written in the code.

 

[rbalex]

...
Also if soemthing does get in to cause an internal explosion then isnt it game over anyway??? If it got in before the internal explosion when wont hot gases get out during or after the explosion.
...

No. See my previous post (#25)

 

[kwired]

I would respectfully disagree as gas pipe is welded and throughly tested for leaks. I would also argue, although I may be wrong in this case that preventing an explosion is easier than containing one especially when you dont know the magnitude.

Welding the raceways would make them tight like gas piping that is welded. Now what about covers on access fittings, switch enclosures, motor starters, and any mechanical operators associated with these devices? Are you going to weld them making them inaccessible or non operable?

 

[iwire]

I am curious I thought explosion proof installations were to prevent the atmosphear from getting into the system not the other way around?

That was what I used to think as well but in fact explosion proof stuff is designed to contain an explosion inside the raceway and enclosures.

 

[mikeames]

Welding the raceways would make them tight like gas piping that is welded. Now what about covers on access fittings, switch enclosures, motor starters, and any mechanical operators associated with these devices? Are you going to weld them making them inaccessible or non operable?

They would be UL listed and sealed for the environment (explosion proof).

 

[mikeames]

That was what I used to think as well but in fact explosion proof stuff is designed to contain an explosion inside the raceway and enclosures.

As I have learned/learning.

 

[kwired]

They would be UL listed and sealed for the environment (explosion proof).

The enclosures we were talking about are also designed to contain an explosion more so than to keep gases out. They have threaded hubs which perform just like mentioned about the threads for raceways. Enclosures with thread on covers perform in ther same way. They also have machined mating surfaces for bolt on type covers. Those covers also are designed to relieve pressure during an explosion and by the time the hot gas has passed through the machined surfaces it has been cooled to a safe temperature to be released in the atmosphere outside the enclosure. This is why you almost never see gaskets for Class 1 equipment. Gaskets also deteriorate at some time and then would be more hazard because they no longer seal gases out.

You also are not supposed to use sealants on threads or for machined mating surfaces of covers as it interferes with what they are designed to do.