Storage Tanks Welding-Current Return Path!

OK...I will put some questions:

i. Won't several amps flowing through the tank rise its potential?

ii. There are other panel too (electrical panels for lighting, grinding etc 220V ). Is it OK to bond the tank and the ground of the panel?

I don't know why but I'm totally confused. Everything has jumbled up :(

If I were you, I'd talk to the people actually doing the work. Then, I've always been funny that way.

Have you noticed that the return conductor is bigger than any earth bond by several orders of magnitude? I'd ask them why, too.

Yes - yes indeed. You don't want to weld into the ground system of the building - ever. Makes for some badly burnt green colored wires. About twice per year we have a welder forget to attach his ground to his table, but the 120VAC outlet box on that table is always grounded - at least until the welder steps on the welding pedal.

"Makes for some badly burnt green colored wires."

Or spontaneous melting of thinwall conduit, if the local zoning mandates all wiring to be in metal pipe, and uses the 'continuous run of metal conduit all the way to the bonding to Earth ground' as a replacement for the green wire (as the Chicago building codes do).

Although, on a circuit that is expected for high amperage, I believe a separate ground wire is 'strongly reccomended.'

Never trust thinwall conduit - we always run a conductor for ground to our 120VAC receptacles.

Eh, it's fine for home or office use, 15-20 amp max per branch circuit, no high-HP motors, no real 240V split-phase branches anymore (unless you have an older electric stove). it's when someone repurposes office space for production without checking the wiring that the problems arise.

Not in our production space - it will come apart with a good bump.

Again, I said "Fine for home or office." I's good enough for the areas of the plant where people aren't actually making things, just sitting around typing on computers.. (pauses and looks to the side, as if making a 'fourth wall break' glance at a camera) ..I even said that the problems arise when an office space is retooled into production space without confirming the wiring.

That's thin wall rigid or flex?

Long time ago I visited the US and had free accomodation in an appartment being renovated in NYC......I noted very different wiring practices to what I learned in Oz.

Onsite sparky was a Brit who was equally unimpressed.

The metallic flex had a drain wire in it close to the conductors' size. OK sorta.

But yeah, conduit is for mechanical protection, not a convenient additional conductor. Gotta run separate grounding conductors most other places, with the metallic conduit,trunking, tray, ladder connected to PE as well.

Only thing safe for industrial environments, which I think the original post started out discussing, as I don't expect they were welding tanks in an office or apartment, is rigid conduit - forklift drivers and crane operators are not perfect. We use flex for devices subject to vibration and then only 3' maximum.The receptacles I mentioned that started this vein of thought, are connected to rigid run the whole way from the panel. I can tell you from personal experience, that both insurance companies and the rare OSHA inspector who actually knows electrical installation, are not impressed with the use of flexible conduit. They suggest removal if they think it is excessively applied in lieu of rigid conduit, even if it meets code.

Don't know about NYC, but in most places in the USA, the current NEC is not applied to existing installations. Get out into the rural areas and we still have knob and tube with switched neutrals on light circuits. I have found a weird wiring application between a receptacle and a light in my house, purchased in 1999, but built in 1969, which I am very sure involves a switched neutral. Someday I'll get time to re-wire that darn thing.

ii. There are other panel too (electrical panels for lighting, grinding etc 220V ). Is it OK to bond the tank and the ground of the panel?

Argued about this for many years, and, to be safe, I always made welding remove my panels first before welding. We too build tanks. Then about 5 years ago I had a Siemens programmer, with many years of field experience, tell me to go ahead and weld when the panel is mounted and the PLC hooked up, and everything grounded to the tank. So far he is right. Even the piezo device in weight cells seem to handle this without problems, and I know the manufacturers still warn you not to do this. (I still remove those before any welding, but others here don't)

So make your own call - remove the panel from any grounding to the tank if it makes you feel better.

Seems I misread your statement about other panels - I was thinking of my controls and thought you meant control panels on the tanks - you are talking about plant panels. No problem, unless your welder forgets his ground. Then you get his current on the plant system ground which is the closest available ground. Not pretty what happens then. Popcorn insulation on the ground conductor if it happens to be on the order of #12 AWG. Be darn sure your welder connects his ground, or if he may forget, then be sure there are no electrical devices with connection to ground touching the tank, such as an automated tank turner.

If the PLC/load cell issue interests you or also applies, the real issue here wasn't the welding current, as it wouldn't flow through the control circuitry, but the 50KHz arc starting signal and RFI.

Yes it is safe to use this method of providing a return path from the welding electrode back to the welding machine and it is the preferred method when multiple welders are being used to repair or fabricate equipment.

However; if the tank is in service and/or there are instrumentation devices mounted on or in the tank, the sensitive devices must be protected from stray current entering their circuitry.

It is best to remove them if possible but often they are protected by installing grounding shunts around them and by only allowing welding to take place in small areas close to the welding ground attachment.

Thanks!

How else would you do it? It's safe enough if nothing inside the tank is flammable.

Thanks!

"But I need to weld that hole shut now before we lose any more gas from that hydrogen tank."

-The last known words of Joseph "crazy Ivan" Warshawski.

(Any resemblance between crazy Ivan and any person, real or dead, is coincidental, unintentional, and a crying shame.)

LOL! Years ago in the sub-zero North part of the USA I was called to determine the reason why no cooling Hydrogen was available to a 600MW generator at a remote site during startup.

When I arrived at the site and went to the incoming hydrogen supply line entry to the plant I discovered the mechanics had connected a 250Amp portable welder ground clamp to the steel pipe out side the building at the pressure control station and attached the "stinger" electrode holder to the pipe where it exited the concrete floor to "thaw it out". (Pipe depth was/is six feet below grade at that location and could in no way ever become frozen at that latitude.)

My adrenaline was so high I was literally shaking as the pipe was glowing red with sparks being emitted from the pipe surface.

I shut the welder off and explained why this was not a good idea to the mechanics and their supervisor. (Crazy Ivan?)

The issue was due to water inadvertently being introduced into the H2 underground piping by an inexperienced operator attaching a water hose to the H2 line.

He had to change the specialty fitting on the H2 line to a standard water quick-disconnect fitting in order to make the connection.

The ID-10T act that initially caused the problem also kept the plant from becoming small particles in space.

We isolated the H2 and used high pressure N2 to purge the piping from the supply tank into the building.

It is a good thing that God loves us all and takes care of those that cannot take care of themselves otherwise the world population would become very small, very quickly.

Dear Mr.magnetic_flux,

It is not advisable to use the tank as grounding source. The earthing cable/bus to be connected to the welding machine properly.

DHAYANANDHAN.S

First off current flows from the negative to the positive. So current flowing from the tank across the arc to the electrode. That's if they are actually welding with the potential as you stated. Most welders have switches to switch polarity or weld with AC. They are bonding the ground to a busbar and welding it to the tank to insure good contact. Poor contact would cause fluxuation in the voltage potential at the arc. Which intern would cause the heat generated to fluxuate. Which would lead to poor welds.

The poor contact would make the voltage potential unspecific.

What you have described is a regular large fabrication shop set up.

Weld your work piece to the nearest welding ground and go.

What is it that you have recently been employed to do at this company?

If all welding machines are not connected together and attached to the tank with a good bond/weld there will be a potentially shocking voltage between the welding machines' grounding connections. The bus bar's use facilitates this. This is often called a ground or common ground.

A grounding rod(s) in the dirt/earth should be used between it and the bus bar. This eliminates any voltage difference between the common use of the tank and the earth/dirt.

The common connection between welding machine at their grounds is actually bonding them together, not grounding them. The connection of this to the earth is actually grounding, connection this to the ground to eliminate any voltage difference between the tank and the earth/dirt. Bonding is common connection, grounding is attaching to the earth/dirt.

Good Luck, Old Salt

I was using the term "ground" in lieu of "work" for terminal description. The terminal not labelled or pictoglyphed as "electrode"

Post was no intention to be critical of anyone else's terminology (basic post, no reply to). Purpose was to explain the possibilities of electrical shocks due to potential differences between sections of the complete welding system.

Also was to inform personnel about the difference between "bonding" and "grounding". As used in welding, the connection between welding machines is actually bonding and not grounding. A connection between these interconnected components and the earth/dirt is grounding and not bonding.

Although this does not normally create a problem in the welding trades, it can be a critical and possibly fatal situation. Welder is transferring gasoline from a metal jerry can into the welding machines fuel tank. Static electricity spark between them ignites fuel fumes and gasoline fire starts. The connection (usually metal cables with clamps on each end) between the components is "bonding" them. The connection (usually cable with clamps on both ends and a conductive rod driven into the earth) between the bonding cable and the earth is "grounding" the system. This becomes a very important factor when transferring flammable materials.

In welding there are many slang names that have become almost standard terminology. For example:

Stringer Bead: a weld made without using a whipping motion (like just sitting 7024 on the work and letting it burn?)
Stinger: a stick electrode holder
Bird Poop: ropey, cold, supremely ugly, blobs of metal made by a noob failing to create a weld
Tombstone Welder: a common AC or AC/DC stick welder that looks like a tombstone in that the dials are on the front and it stands upright.
Stick Welder: one capable of doing Shielded Metal Arc Welding (SMAW)
Clamp it Jed: put a clamp there
Golden Arm: a really good weldor

"Welder Weldor": It's yelled when the fit/prep guy is done. Means "get your arse up here and burn rod"....lol

Drinking hand: A drinking hand is a welder (or anyone else I suppose) that drinks alcohol in excess. A welders is never called a wino, but drinking hands. And being a drinking hand isn't actually all that bad a thing to be

"Making popcorn": machine not set correctly (mig)

"looks like a ****ing alligator bit this off": Jagged cut with torch

"Neck down" ...as in I'm not getting paid to think, I'm getting paid to burn rod.

W.A.S.P. Welders Against Stupid Pipefitters
"Dogleg" two pieces of long run pipe welded together crooked.

Got to go now, "looks like Johnny cutter is using worms for a square again".

Good Luck, Old Salt

The procedure they are using is perfectly correct and since the size of the anode versus current carrying path is a large area conductor surface, there should not exist an appreciable voltage drop issue for this type of utilization. If you have any doubts calculate or measure the resistance & voltage drop parameters to determine if this is a concern or not. It appears that it is not, since you don't mention that they are having problems with weld quality or any other weld quality issues. Regarding the safety issues of the procedure, I don't think you should have a concern since this is common practice in the industry. If in doubt regarding safety, please consult the 2014-National Electrical Code (NEC/NFPA) for welding apparatus applications and operation.