Welding while still rigged to an overhead crane

Date 01-20-2010 12:55

Jettamk3
Welcome to the Forum
Always remember the more information you can give the better the forum members will be able to answer,
The main problem I see is the part being welded wanting to get it's ground from the chains.
We have had to do welding on hanging parts and have made sure the ground was from the welding machine.
I have experienced no problems this way but I am not a metallurgist.
Again Welcome to the Forum
Good Luck
Marshall

By jwright650 (*****)

Date 01-20-2010 13:35

If you can find any arc strikes on the inside/outside of any of the chain links, I would permantly remove the chain from service. Arcing through the bearings, cables and whatnot on the crane cannot be good for those parts. And if the welder is getting any grounding through the crane itself, then there is a possiblity of the current finding the path of least resistance through the crane. Not an ideal situation in my eyes.

I thought there was something in OSHA 1910.179 or OSHA 1910.184 that didn't allow this practice, but I glanced through it a minute ago and didn't see anything.

By Lawrence (*****)

Date 01-20-2010 14:42

This is one precaution I found in:

ANSI Z49.1 Safety in Welding Cutting and Allied Processes

11.3.4 Prohibited Work Lead Connection. Chains, wire ropes, cranes, hoists, and elevators shall not be used to carry welding current.

By jwright650 (*****)

Date 01-20-2010 15:05

That is what I was looking for...I looked in the wrong section. OSHA 1910.254(c)(2)(iii)
Thanks Lawrence.

By rlitman (***)

Date 01-20-2010 14:48

Current must flow in a circuit. If an insulated hook is installed on the crane, and a ground lead is properly attached to the workpiece, current cannot flow out through the crane.

By spots

Date 01-20-2010 16:43

In a shop I worked at we used a short nylon choker between the hook and the bridle ring to prevent welding current from traveling through the crane/rigging.

By js55

Date 01-20-2010 16:50

But lets be clear here, welding current in and of itself does not damage chains or cable chokers. The problem is if the grounding is not sufficient and arc strikes occur which does damage them and renders them unsafe.

By Lawrence (*****)

Date 01-20-2010 17:18

Now you are confusing me (typical when somebody tries to make something clear to me)

Current in and of it self... Does damage cables and chokers *if current is carried through them*

Current may pass through an item that is chained.. Passing from the electrode to the work clamp.. As long as the current does not pass through the cables, chains, chokers.. Things are safe and compliant.

If the chain, choker or cable becomes part of the circuit.. This is the danger and non-compliance.

Right?

By js55

Date 01-20-2010 20:08

Lawrence,
I'm talking about metallurgical or mechanical damage to the material.
Current in and of itself will not cause mechanical or metallurgical damage to the material.
I'm not arguing whether or not it is safe.
The original post talked about crystallization.
There will be no phenomena of crystallization just from current.

By ssbn727 (*****)

Date 01-21-2010 01:40 Edited 01-21-2010 05:16

Hi Jeff!

I agree! One would have to include how much CCV voltage is being used to keep the current flowing as well as how much resistance would occur which is also dependent on both the material and whether or not there is any insulation to prevent some electron loss also...

So it is really the amount of resistance occurring within the chain that would be the culprit for enough residual temperature increases to occur for a certain amount of time to possibly cause changes in the crystal matrix, at random locations, yet more likely closer to the opposite end of where the current is starting to flow across the chain from unless of course, if the polarity is reversed which would cause the opposite affect, and thus affect it's metallurgical properties as well as it's mechanical properties also regardless of where the current originates from.

Which means that there would have to be a whole lot of current passing through, and being forced through the chain by such a little amount of Closed Circuit Voltage (CCV) in order to create enough resistance that even if the chain were not insulated, the electrons would still congregate at random locations without dissipating through the conductor itself (chain made of steel which has a much higher resistance than copper, or aluminum for that matter, and the length of the chain also has to be taken into consideration too! ) for such an amount of time for this phenomena to occur - CAPECHE???

So, a low enough Open Circuit Voltage setting (OCV), and the increased Resistance of the metal especially at locations away from points of contact between the links of the steel chain, in combination with the amount of current being forced through the length of the steel chain for a certain amount of time would all have to be present in order for this phenomena to occur... Clear as MUD - RIGHT??? :) :) :)

Respectfully,
Henry

By ssbn727 (*****)

Date 01-21-2010 05:13 Edited 01-21-2010 05:19

Well, if anyone understood as to was I was attempting to explain, it would be that current alone would not cause crystallization, because there would also have to be enough resistance as well as a low of an amount of CCV voltage (Which occurs if the power source operates at such a low Open Circuit Voltage, or OCV.) available for this phenomena to occur which is much like describing what happens when one applies an arc to the chain... The circuit closes, and the voltage is even lower which would then cause an increased amount of resistance which would then create more heat within the chain which is the conductor, and not too good a conductor in fact!

I also agree with Dave's comments regarding an improper grounding of the chain which would cause arcing where the work lead would be connected on the chain...

HF is also a big NO-NO as well as Dave mentioned also. :)

By js55

Date 01-21-2010 13:48

I'd like to add, and I'm sure most in here are already aware of this, I'm not even sure what is meant by crystallization.
The metallic structure of the chain or cable choker will be already crystaline. Metals are essentially crystals with orderly microstructures.
If by crystallization it is meant re-crystallization then it would be equivalent to violating the lower transformation temperature which would require a great deal of heat as indicated by Henry.
If by crystallization it is meant embrittlment then again it is a function of the heat imposed.
In any case, as Henry indicated it would require a great deal of current. And the chian/choker would yield/break before these metallurgical conditions became permanent.

By Metarinka (****)

Date 01-22-2010 20:00

I understood you. sending electricity through a piece of metal alone is not dangerous (unless of course resistance is high enough to melt it or hit the lower transformation temp).

the danger comes in arcing that can damage structural components, causing embrittlement, work hardening, or annealing.

that's why it's accepted you would never want to ground to a structural item such as a chain or hoist, or crane, or boom.

Back in my art days I used to weld chain all the time, and of course it would be the ground.

By ssbn727 (*****)

Date 01-22-2010 20:32 Edited 01-22-2010 20:37

Joel,

No one is disagreeing with what you, or Dave, or Allan has pointed out with respect to arcing via improper grounding and so forth... Both Jeff and I were just pointing out that current alone and in of itself cannot cause this if everything is is handled properly in order to prevent any possible arcing, or sending feedback current on a higher frequency level which could fry some unshielded electronic instrumentation and control components found within the crane itself...

So there's no disagreement with respect to the potential dangers regarding welding of chains attached to cranes, or anything which the chains are attached to that is conductive to cause similar conditions... Larry was simply requesting some clarification. That's all. I hope this clarifies the points Jeff and myself were trying to point out. ;)

Btw, as a Boilermaker/Tube welder working inside many a power boiler in both shut downs and new construction we used an awful lot of chain hoists and other rigging equipment, and we knew how to properly ground components to weld even with the chains on that were attached to boom cranes and such... The same applied when I worked at Electric Boat building Nuclear Submarines for the US Navy.. So I think that I'm speaking from a good amount of experience which accumulated to approximately 20 or more years in these matters. ;) In other words, we knew when to use nylon, or hemp slings and other associated equipment in order to isolate from potential arcing of the chains, cables, etc. :)

Respectfully,
Henry

By DaveBoyer (*****)

Date 01-21-2010 02:51

At the auto frame plant We had to unhook the crane before any welding.

As to the harm that might come if the crane was hooked up, it would be the result of poor work grounding.

There are a few different posibilities:

1) Arc damage to chain, hooks, bearings, etc.

2) Stray electric current/voltage damage to the electrical & electronic components of the crane & controls.

In the case of 1) arc pits do cause localised hard spots in heat treatable materials. The pit is the stress rizer and the untempered martinsite cracks easily, bad combination in a structural component. Arc pits in bearing surfaces lead to premature bearing failure.

In the case of 2) there is aditional risk if High Frequency is used in the welding/cutting process. Proper isolation and grounding of the crane's electrical/electronic components should eliminate issues from the welding current itself, but better not to tempt fate.

Connection of the welding work lead to building structure increases the chances of problems in situation 1) & 2).

By joe pirie (***)

Date 01-21-2010 03:09

working on a job a few years back we had a pipe section being supported by 3 chain falls. two welders
were welding on the pipe doing tie ins. one of the fitters went to remove a chainfall after the hanger was installed
and burned his hand pretty bad somehow the chain had become grounded and became extremely hot. I really don't know why it
happened but now if im going to held on a suspended pipe i always use a nylon choker.

By aevald

Date 01-21-2010 03:43

Hello Dave, replied to your response as there were numerous ones here where my comments might have fit. I have run into instances where the building grounds, panel grounds, and other grounds in a particular facility shared electrical continuity to varying degrees within a given facility. In a case such as this, IF.... the machine welding ground wasn't properly connected or had a poor connection, the ground side of the welding current might try to make it's way through the crane hook up the cables/chains to the bridge and from the bridge to the bridge/gantry ground and associated circuitry, hence making all of these components susceptable to arcing in the right instance or scenario. Definitely not necessarily the norm(we hope) yet still entirely possible when certain conditions exist. As you mentioned, any arcing of cables, chains, or any other lifting rigging renders them scrap. Hence, properly rated and applied nylon slings, rated and electrically isolated intermediate hooks, or other electrically isolated rigging should be used or welding should not be allowed. For what it's worth that's my additional $.02 Best regards, Allan