de-Gaussing magnetic pipe prior to welding

[kstaylor]

Does anybody have a sure-fire way of de-Gaussing a piece of 9Cr-1Mo pipe in order to make a GTAW weld? The section of pipe is magnetic and plays havoc with the arc from the Tig torch!

 

[Dan76]

Try coiling insulated wire around the pipe, continuously until the needed length is covered plus a little extra (I would use 2 pipe diameters on each end, with a minimum of 6 inches <15 cm>) Pass a DC current through the coil, then halve the value of current and reverse the polarity, repeat this several times (6-10 should be Good)for 3-10 minutes each time halve and reverse current each time. Do not exceed the current rating of your wire, use a variable voltage power source (A welder should do nicely) and use ohms law V=IR (Volts=Amps x Ohms) to determine voltage settings (If necessary insert a resistor in the circuit to limit the voltage, an incandescent light bulb should work in a pinch). Borrow a multimeter to check Voltages and Resistances. This should De-Perm your pipe.
If the problem is from Induced magnetism this won't help in that case try to move the pipe out of the Electromagnetic field causing the problem.
Good Luck, -Dan76

 

The only way to successfully eliminate or nuetralise the effects of a magnetic field in pipe is to wrap the coils or additional coils around the pipe and run AC current through them during welding. The alternating current misaligns the domains in the material and thus reaks havoc on the magnetic field. All demagnetising operations are performed using AC coils. In addition, some Magnetic Particle Inspection Units employ a 30 point step down feature, which not only uses AC current, but also slowly decreases the current until the magnetic field is minimised. Anyone involved with Nondestructive Testing can verify this. This is done in the NDT field on a daily basis.