I am building a fence using 2 7/8" heavy wall, used oilfield drill stem pipe. I am using
a stick welder and 6011 rods. Being oilfield pipe, it is very clean inside and outside. The
problem is that often a break will occur right next to the (bead) weld area. I have a good
bead with excellent penetration. A local welder said that sometimes pipe used for drilling
purposes will become magnetized thus causing the problem I described. He suggested
that I try wrapping the ground cable clockwise and counter clockwise around the pipe
several times before I clamp it to see if this helps. He said that the 6011 rod was probably
a good rod to use and that a 7018 would give a stronger weld but it would not solve the
problem. Has anyone ever experienced this problem? Would switching to AC or DC help?
Is there a better rod to use? I only have access to a stick welder. I would appreciate any
adivse anyone can give me. Thanks!
By -
Date 10-16-2000 18:02
I would recommend AC and/or try relocating your ground.
If the material is magnetized and your not getting a situation known as arc blow ,which is related to the current passing through the material , then you may be able to reduce the magnetism by striking the pipe with a hammer.
I should know a better way but I've tried the welding lead wrapping, heat, and strong blows with a hammer. They have all worked at varying degrees at different times. The hammer takes the least effort.
Someone else probably has a more technical answer.
Good Luck
It sounds like a materials problem, and not a residual magnetization problem. Keep in mind, "drill pipe" is not standard pipe material due to the stresses it is subjected to. More than likely you have high alloy or high carbon pipe. Try preheating the area to be welded (without knowing specific chemical composition of the pipe, a good starting point will be around 300 degrees F.) A higher preheat may be required, again, I doubt if magnetization is the source of cracking.
By -
Date 10-16-2000 21:30
OOPS I missed the part about the cracking . As far as I know the magnetism will not affect the cracking.As DGXL said try the preheat. 7018 is also more crack resistant but with crack outside the weld area it may not be a contributing factor.
Heat affected zone cracks are sometimes caused by cooling rates. I would do as DGLX suggested and preheat. This will also reduce the amount of hydrogen present if hydrogen induced cracking is a problem. With oil field pipe you could have an alloy pipe that is susceptible to cracking. Go to a low-hydrogen electrode like E7018 and if you are still having problems after the preheat, then you may try a post weld heat. This will reduce the cooling rate and help with the cracking. Good Luck.
Definitly preheat. Dont be bashful, 500 F isn't too high.
Drill pipe could be approaching 100 ksi tensile strength. I had some casing that was 80 ksi yeild. Actual yeild was closer to 90, with ultimate around the 100 mark. Since chemistry is pretty close to uncontrolled, carbon equivelent of the same grade of casing ranged from a low of about .52 to over .8.
Drill pipe may have been used in a sour (H2S) environment. Preheating would be required just to remove the hydrogen that has been 'absorbed' by the pipe while drilling.
Thanks to all who responded to my post. Your help is greatly appreciated.
Guess I caught this one too late, but wasn't there also some radiation hazard associated with using oil field piping making it illegal in some cases to use it ?
What kind of radiation hazard would there be?
You have the answer but let me add a couple of bits of information. That oilfield pipe has chromium and molybdenum alloyed with the steel. Excellent high strength material! But when welding it, it does not like hydrogen. Hydrogen causes cracking, preheating drives off the hydrogen and is good for 1/2 inch and thicker wall material. It is not necessary for 2 7/8 tubing if a low hydrogen process like GMAW (MIG) or SMAW (Stick) with a EXX15, 16, 18 or 28 (AWS classification) electrode like the E-7018, E-7018A1 or the E-8018-B2. For good control welding out of position use the 3/32 diameter electrodes.
This used tubing can be highly magnetized. You will notice after grinding the end preparation the iron filings sticking on the end looks like a welder's unshaven face, stubble sticking out all over. If you have a machine like the Miller Syncrowave 250 use the AC which is squarewave with an adjustable balance control. Turn the control to maximum penetration and change the weld cable connections so that the electrode is on the work stud and the work connection cable (work ground) on the electrode stud. (Remember to switch back when re-connecting the GTAW (TIG) torch!!). If you don't have have a squarewave AC welding machine use an AC or AC/DC machine on AC and use a E7018 that is designed for AC. This is an electrode that is designed specifically for "Buzz boxes". This type of electrode will work on DC as well.
If you want to use an engine drive you can't beat the Miller Legend or Trailblazer on AC!
