I am looking for industry best practices related to welding from a suspended platform or scoffolding.
My company recently had an incident on an offshore oil platform, where a welder was working from a steel man basket suspended from a pedistol crane. The certified welder was using an arc welder (grounded to the platform's deck) to weld a piece of steel to the oil platform's exterior. While he was making his weld, the man basket came in contact with the oil platform resulting in an arc at the point of contact. The electric current traveled through the man basket, up the 4-point wire rope rigging supporting the basket, and finally up the crane's wire rope whipline. Minor arc burns were visible at all the points where the current crossed a gap.
Luckily, no one was hurt and the damage was minor .
My question is, what (if there is one) is the industry practice for welding from a suspended platform? It seems that the man basket should have been grounded to the oil platform with a separate grounding cable that would ground the basket directly to the platform rather than being grounded indirctly to the platform through the crane's whipline and rigging. Does this seem like an acceptible way to prevent arcing should the basket contact the platform? Are there common or special safety precautions that should be used to prevent such a situation- other than the obvious not welding from a man basket?
Thanks in advance for your advice.
Mutz
It sounds like the problem was most likely caused by the insulation being torn on the welding lead at some point, allowing the lead to ground out on the man basket. Of course this can be prevented by checking and taping up any bad spots in your lead before using it, but we all know, as simple as this is to do, it's almost impossible to keep a lead in one piece. Especially in an oil field enviornment.
Anyway, it's good that no one was hurt, but keep in mind the safety and equipment hazard still exists. The Whip line and the Main Hoist line on the Crane needs to be inspected for damage. You sure don't want them to snap under strain of the next heavy load. Also, the most important thing to stress about welding around Pedestal Cranes is that if your ground is allowed to run through the crane, it is arcing out on the ring gear bearing that is supporting the crane as it pivots on the pedestal. While this is not a personnel safety concern, it is a major equipment concern as it is easy to ruin this bearing this way. It will cost as much as the crane is worth to replace the bearing.
Because you do not want to ground through the crane at all, grounding out the basket to the rig is not recommended.
Be safe out there!
Tim
There is more to this story than you are telling, In order to do that kind of damage the man basket had to be part of the circut as TimGary suggested.
Some one got careless and possibly droped the stinger where it could make contact or as Tim says has bad insulation on the leads. Hanging the leads from a rope below the basket may help that problem but for the other possibilities an insulating fire proof cover (glass blanket) for the basket could prevent a lot of oopses.
I have done alot of welding from crane baskets, although not on oil platforms. One thing I do that many people do not is bring the ground lead up with me and ground next to the point of welding. If you follow the advice of the two previous posts and bring the ground up with you, you will solve most of your problems. Admittingly you will never solve the problem of a sloppy or careless employee, but these points will undoubtedly help.
Respectfully,
Mike Sherman
Shermans Welding
Mutz,
Although I possess no expertise in the field, I would agree with Tim's assessment that the arcing was caused by the inadvertent, and almost inevitable, contact of the electrode lead with the basket. It would seem to me that the crane and the basket and parts to be welded are all on the work side of the welding circuit. So, grounding the basket to the rig may prevent current from travelling through the crane but not necessarily, it would depend on which path offers the least resistance. I think the basket should be isolated from the crane with non-conductive rigging and from the platform with non-conductive bumpers.
Dave
By mutz
Date 10-07-2002 17:54
Thank you all for your replies. I will recommend to the crew that when welding from a man basket they need to cover the basket with some form of non-conducting insulation to prevent inadvertent arcing. I also think that using non-conductive rigging is a good idea, but not sure if it is acceptable by OSHA regs. I will look into it. I will also re-enforce the importance of inspecting the welding leads and connections prior to starting work.
I will also pass on all of your responses to the facility supervisor and welding crew.
Bye-the-way, the crane, whipline, and rigging were all inspected immediately after the incident by the company's crane maintenance crew. Everything checked out OK.
Thanks again,
Mutz
