Welding Magnetic Drill Piple

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I've been hearing complaints about how hard it is to weld used drill pipe that's become magnetized.  Never welded it  myself but a friend who's welded a lot of it was wondering exactly what goes on.1.  First, how does it get magnetized by rotating in a well bore?  It does contact the steel casing in places,2.  Does it really get magnetized or is this an "oil patch legend"?  I've never seen any iron filings or other ferrous material sticking to it.3.  I know that magnets lose their magnetism when heated above a few hundred degrees F.  Welding is a lot hotter than that.   If it is indeed magnetized, how can it keep enough magnetic field at welding temperatures to affect the arc?I suspect that maybe it isn't really magnetized but picks up contamination from drilling mud that  makes it difficult to weld.  But if I knew much I would be asking these questions in the first place.  I'd sure appreciate any explanation than anyone can provide.Thanks,Bob
Reply:Dont know about the pipe becoming more magnetic than it already is, but this link might have some pertinent info for you...scroll down.http://www.weldingweb.com/vbb/showthread.php?t=10219ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:Thanks, I dunno if that thread answered my specific questions but the part about the austenetic, bainite, pearlite, and other stuff forming depending on the rate of cooling is worth printing and sticking in a tool box.I'm off to a great start here, my first post and I can't even spell "pipe" right. Sorry about the typo in the title.Bob
Reply:A little Anecdote...Many years ago I went on a boy scout camp out in central Texas. The purpose of this camp out was to earn the orienteering merit badge. This merit badge is based on the idea that it is important to take a bunch of hyper-active 9-14 year old boys out into the middle of nowhere and attempt to teach them how to use a cheap, plastic, official Boy Scouts of America branded, made in china, compass to navigate.For the final portion of the merit badge requirements we were given a list of directions along the lines of: "go XXX paces on heading XXX then XXX paces on heading..." and so on. The idea was that if we had properly learned the use of the compass we would end up at a certain point, give or take a few yards. Now, the area we camped in was bordered on one side by a small river and on all other sides by grazing land, almost completely devoid of trees and crisscrossed by a few barbed wire fences. This was also in the middle of a drought in the middle of summer so the average temperature in the shade was well into the triple digits. When we asked the scoutmasters why they chose this time and this place for this camp-out they only smiled and said, "because some other troop already booked the surface of the sun."So, the scoutmasters sat down in lawn chairs under the only shade tree within walking distance with big glasses of ice water, handed us our direction sheets and sent us hiking off into Hell's Frying Pan (except for one scout who held his compass backward and ended up stuck in a thorn bush on the other side of the camp).In theory, we were supposed to end up back under the shade tree where some chilled water would be waiting for us. In reality, after trudging across Dante's Inferno, struggling over barbed-wire fences, and dodging angry bulls for three hours, we ended up about a mile from camp...It turns out that one of the more sadistic scoutmasters thought that it would be absolutely hilarious to put one of our way-points about two feet from the end of a short section of a steel pipe fence....And How It's Relevant.That day (after recovering from dehydration), the whole scout troop learned about the Earth's magnetic field and what it does to iron and steel. See, when something magnetic like pipe or I-beams or any piece of steel is left sitting in one place for long enough the Earth's magnetic field can magnetize it. The magnetic field of the Earth isn't very strong so it takes a while and when something like a piece of pipe gets magnetized in this way it's not very strong (like you observed, not even strong enough to attract iron filings). However, the plasma column (a.k.a. electric arc) used in welding is extremely sensitive to any magnetic fields and will wander around causing a phenomenon we call "arc blow." Arc blow is easy to recognize because when it happens it will appear that the welding arc will go just about everywhere except where you want it to go.I've heard many stories from the old-timers (read: instructors at school) about pipeline jobs where the job stalled in the middle (usually for funding reasons) and the rest of the pipe would just be left in a field. By the time the project would be resumed, the pipe had been magnetized so much that the arc blow made it nearly impossible to get a decent weld.I suspect that any drill pipe that one would be welding on will have already been (more-or-less) discarded by the drilling company and has been sitting in a field or storage yard for quite a while. It probably won't always be magnetized, it depends on where it was stored. If it was stored in a building, the building might have disrupted the Earth's magnetic field enough to prevent the pipe from being magnetized. If it's been sitting in the middle of a field for a while (like the pipe fence in the above story) it stands a better chance of being magnetized.Anyway, you are correct in that, when heated, steel will lose it's magnetism. In most steels that temperature is around 1333 degrees F (this number varies depending on alloy), where the grain structure turns to austenite, metallurgists call this the upper transformation temperature and physicists call it the Currie point.The metal in the weld puddle itself as well as the base metal near the weld does get hot enough to lose it's magnetism, but this doesn't solve the arc-blow problem because the rest of the pipe does not get hot enough to be affected and is still close enough to mess up the arc. You could try heating the whole pipe to above red-heat, but that would probably take a lot of fuel and time.Another way to demagnetize the pipe is to use a degaussing tool ("gauss" is a measurement of magnetic field strength). A degaussing tool is just a big coil of wire that has alternating current flowing through it that you pass the pipe through (the constantly reversing field created by the coil will cancel out and eliminate the magnetic field in the pipe). However, degaussers are very expensive and take a whole lot of juice (electricity) to be effective.The easiest way to combat arc blow is to use the magnetic fields created by the welder to cancel out the fields in the pipe. You can do this by moving the work clamp around and/or coiling the work lead around the pipe. While this is the easiest method, it's not exactly reliable. Magnetic fields are complex and finicky things, sometimes the only way to fight them is head on.Visit Tensaiteki.com
Reply:Tensaiteki--         "A little Anecdote...            ...And How It's Relevant"  Great explanation!!  I wonder if a length of iron would magnetize if stored vertically from the earth instead of horizontally???  I suspect not, but???
Reply:Originally Posted by sail2uTensaiteki--         "A little Anecdote...            ...And How It's Relevant"  Great explanation!!  I wonder if a length of iron would magnetize if stored vertically from the earth instead of horizontally???  I suspect not, but???
Reply:Hmm...good story. I just use AC to combat it if I have to. Seems to work.
Reply:Tensaiteki,Thanks for taking the time to make your detailed post.  I didn't realize that the temperature at which steel loses its magnetic properties is so high, I thought it was in the hundreds of degrees F range.   And I never thought about pipe getting magnetized by the Earth's magnetic field just by laying on the ground.Bob
Reply:It is true that the earth's magnetism can magnetize steel when laying north to south. also in order to remove magnetism with coils you need to use more magnetic force then what got it there. also mild steel easily magnetizes but doesn't retain magnetism as well as high carbon steels, Just like high carbon is harder to magnetize but retains magnetism very well. Now as for welding, magnetism creates arc blow and there are some thing's that you can try such as turning amperage up, dercrease rod to puddle distance, and changing direction of travel.
Reply:I've never tried this myself, but I have an old physics book that says you can magnetize a steel pipe or rod by laying it in a north-south direction and strike it with a hammer. The pipe can be demagnetized by laying in any other direction and striking it again.Miller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:The magnetism mostly comes from when the pipe is inspected.  It's a bitch to get out cause drill pipe is very hard and has lots of retention.
Reply:I spent 23 years in the pipe inspection industry and the demag saying was to heat it, beat it, or ac it.  Ac works sometimes but the only to demag is to introduce an opposite magnetic field in the opposite direction.
Reply:If it's magnatized, you can take a torch and heat it.  It should lose its magnatism
Reply:I have been on jobs before as a fitter when i was younger, in which we would wrap the leads around the pipe, + and - then try welding it. If it was worse we would reverse the orientation and try again. The welder claimed it work like a charm and seemed to do a good job welding it after we wrapped them.Millermatic 251Century 180 migSpectrum 625 Syncrowave 250DX
Reply:And the magnetic pipe is any different form a magnetic jig holder used to hold two pieces together?
Reply:Drill pipe is hard to weld even if not magnetised.  It is very hard and requires lo-hi at least.  The most common drillpipe is 75000 tensile where normal pipe is 40000.  This also makes it retain magnetism however it's induced.  It only gets worse if the pipe isn't E grade.  S grade is 90000, G grade is 105000, and S grade is 135000.  If it it magnetised you don't have a chance.  Believe me I know from experience.