Demagnetization of Pipe Ends

IDOFED partners with reputable OEM and handle Demagnetization of pipe end including training of personnel.

After Pipe is strung on the right-of-way, the ends are typically magnetized, for different reasons. If this magnetization is severe enough (>10 Gauss) it will cause Arc Bend (or Arc Blow), which causes the weld arc to move from the intended area. 

Blow is unpredictable to its direction or severity and can only be compensated by a good journeyman when using a ‘stick’,
Automatic Welders don’t have a closed loop feedback system (brain) like a journeyman, so blow cases a greater degree of problems, for each hot pass. 

Demagnetization in the field has often been attempted by wrapping pipe ends with welding cables and striking an arc with a welder switched to an AC field. If the arc is stopped when the sin wave crosses zero, the surface of the pipe will be demagnetized (due to the skin effect of AC), however the field will quickly return to the ends and even faster to the bevel. If the arc is stopped at the maximum amplitude (positive or negative) a new magnetic field will be induced into the pipe, which may be even stronger on the surface.

Magnetic Fields are easily measured with a Pocket Magnetometer (Gauss Meter). The only reliable way to Demag the ends of the pipe is with a Reversing and Decaying DC procedure. This can be accomplished on individual ends or to 2 pipes that have been brought together (for a repair). First, we will deal with new construction where an operator has been sent ahead of the
Welding Crews to Demag all pipe ends. He simply sits the appropriately sized Coil on the end of the Pipe, as illustrated to the right. Using his separate control panel, he quickly energizes the coil and induces a controlled magnetic field. He then reduces his amperage setting and reverses his field direction, again energizing the Coil. 

This procedure is repeated for a total of 5 to 7 times, depending on the wall thickness and diameter.