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I know this discussion has been beat to death and I have heard about wrapping leads or moving your ground but I was wondering if anybody has taken a mag yoke to try and demagnetize or change the amount of magnetization in pipe when magnetized pipe is an issue. Next time I run into some magnetized pipe issues I was thinking of experimenting around with a mag yoke to see if it improves the weld ability of the joining pipes. Was thinking maybe someone has already played around with this.
It would depend on the strength of the residual field and the wall thickness of the pipe. it would make sense to at least give it a try. Nothing ventured, nothing gained.
Best regards - Al
I've tried it, but it didn't work very well. I'd be interested in knowing what circumstance the pipe became magnetized?
Gerald
In the Pipeline field a lot of the pipe we receive is coated with FBE Fusion Bonded Epoxy. It's applied to my understanding like powder coating where the pipe is magnetized so FBE sticks to the pipe and then they bake the coating on. Then they demag the pipe but sometimes there is residual magnetization left or they did not demag it well enough thus causing problems when welding the joints together.
Delux,
I've been dealing with this problem on some SAW fixturing that is so magnitized it will hold almost a 1/2 pound piece of steel to it.
I started with the old method of just doing some AC SMAW on the fixtures to reduce. This wasn't good enough.
I talked to a guy who is smarter than me and he instructed me to get the same AC power supply hooked up for SMAW with a large electrode, clamp or tack a piece of scrap to the magnitized part and the work lead to the other end; and make a dead short with the electrode. Let the short keep the circuit closed until the electrode is overheated or the machine poped a breaker, rince repeat.
This method broke up the magnitisim better than anything I've tried before...
Don't know if your welders produce AC... Maybe Cactus can ship you a Vantage over there.... That would prolly just scare that magnitisim away :)
Lawrence,
The only good Vantage of a disadvantage is a if you own a yacht and need a good boat anchor. ROFLMAO!!!!
I have inspected FBE, and witnessed it's application. They used a high frequency alternating current magnetic field. They did this for induction heating, as it is heat that activates it (typically between 225c and 245c or 447F - 473F). Arc blow is usually =>50 gauss (50 x 10-4 tesla).
While it has been several years now, I have worked the firing line, and have seen magnetized pipe as you say, but it does not always come from the pipe mill.
I ran the whole 150 miles on the firing line this job and arc blow wasn't really an issue this job. The yoke deal was more of an idea that popped in my head. We had actually more problems with bad batches of rod than anything. If it does not always come from the pipe mill where else might the magnetization be picked up in terms of new pipe? Not inservice pipe.
http://www.britannica.com/EBchecked/topic/586372/telluric-currenthttp://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.htmlThe same science behind how a yoke works, applies here. It's more often a problem in northern areas than in southern areas. Pass a current from any given source through a ferromagnetic steel and it will create an electromagnetic effect. Do so with DC current, and it runs the risk of magnetizing the material. The sticks usually would have to be laid out north to south as the wavelength for telluric currents are long and won't affect east west orientation.
There was a long time I though all that was BS, but I've since been shown the light via pipe that had no coating, or otherwise any interaction with anything magnetic, yet it had a residual field.
I've heard of this but not tried it.
I do however, know that energizing a yoke on material that is in the process of being welded is a good way to burn up a yoke...
Tim
A month or so back, I was welding on a job where we replaced a 150' section of 34" x .375" mainline pipe. After the cut and prep, the magnetism was reading over 310 gauss. At 3 or 9 o'clock on either end of the buried pipe, a 12" crescent wrench would stick to the land and hang there perpendicular. We had a spare Classic 300G on site and so we wrapped 9 coils around the pipe (on 34" pipe that's about 90' of cable) near the joint and we had the gauss meter on the land. We got the Gauss to read exactly 0 by putting it in 4th gear and at about 70 on the fine current. We kept it there for the fit-up and the bead, hot-pass and fill. Those leads were pretty warm! Worked like a charm though.
Better to demag with one of those dog gone vantages welding on the job.....just hook up both ends and shoot some low current ac. That will pull that pesky arc blow right out of that pipe.
Least they are good for something on the pipeline!! LOL luv ya RC sry man
Somebody mentioned Degaussing?
Well, it's not a pipeline but this is how we do it for our submarines which do need to be degaussed before they go out on patrol... Btw, it's sometimes coined as "Deperming."
Respectfully,
Henry"
Really cool pictures Henry.
M.G.
Great pics Henry.
I wonder how come the fields don't mess with the navigation systems. It sure wrecks havoc on our land nav. systems in our vehicles.
Tyrone
What an assume job you have! good on ya
This is coming from the MFE tools in the smart pigs. When the operators run the inspection tools they are introducing magnetism into the pipe.
Give the positive 7-9 turns clockwise and the ground the same counter-clockwise. Hang a rod in the bottom of the bevel. The magnetism will hold it!
When you touch the electrode to the top, if you have enough rounds on the pipe the rod on the bottom will drop. If it does not drop off, add a couple of rounds and check again. If that does not work, change the directions of the leads. Positive go counterclockwise, negative clockwise.
Pipe running north/south tends to be worse.
thats interesting about the subs. I know that the winners of the last baja 1000 owe their victory to magnets and shortcuts more than anything
Just curious as to why no one has mentioned the small portable de-gaussers, which can reportedly degauss a cargo plane load of pipe in hours? Anyone used one, or owns one?
SSBN
Those first 3 look like the one in Ingleside, TX
That's the one!
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