Structual Magnatisum 3

[RickFriesen]

I'm a welder that is working on structual steel replacement in a mining refinery. I'm having a hard time with magnatisum that isn't present untill the column is cut. Its so strong that it will hold a 24" pipe wrench. I've heard different oppinions towards DC and AC. I'm wrapping the column with the ground and using Electrical bonding cables but nothing is working. The magnatisum is to strong. Any ideas on how to weld with this.

 

[Ron]

You might try hooking another welder's ground clamp to the piece and reversing the polarity, while welding AC.

 

[kgmPE]

The residual magnetism is the result of the steel at the cut freezing in the presence of a magnetic field (the earth's, although I've never seen such a spectacular example), or due to DC welding/cutting current flowing through the liquid steel as it is freezing. Try heating the cut edge with a torch. Once its above the Curie temperature, it will lose its magnetic properties. You can test for this temperature using small piece of steel or a small magnet...when hot enough, it will not be attracted to the cut steel. Then let the steel air cool. It will still capture some of the earth's magnetic field, but with much less strength. Even better would be using a demagnetizer, such as those used for bulk erasing magnetic audio recording tape, or the type used for demagnitizing tooling in machine shops. Note that these devices are duty-cycle limited, so you may only be able to partially demagnitize the steel before a cool-down period is required. Here are some examples of the machine shop type:

http://www1.mscdirect.com/CGI/GSDRVSM?PACACHE=000000128773504

#09180019 should work, and is not terribly expensive.

 

[RickFriesen]

Hey thanks for the help. We even went to a demagnetizer. Its run cycle was 3.5 min. for heavy duty. I ran it constant for 2.5 hrs. It went from 1750gause to 1200gause. Still unweldable. They turned off the cells in the refinery and it trickled down in 3 min from 1750gause to 1200gause, then one cycle on the demagnitizer and it was under 200gause. Finaly a solution. Short lived, the refinery refuses to shut down for the replacement and we must do it on the run. Even with cutting the columes with a grinder zip cut, the magnatizum is still there. We found plating across the joint lowered the gause, no need to clamp them, they just stick there. Heating a spot on one side of the web and welding on the other side to start an arc, then go slow and stay in your weld puddle, don't drag the puddle. Crank up your weld temp and let your puddle preheat the upcomming steel. Stuff a piece of angle iron into the back side of the cut, again it just sticks there, as you weld the mag. dissipates and the ange iron will fall away. One pass around and the mag. is gone. This has worked on all colums so far. The gause meter would only read up to 2000gause. One column would reset and malfunchion at an inch from the cut site. I'm not saying its easy but it is possible.