P5 pipe magnetization

Date 06-10-2009 20:17 Edited 06-10-2009 20:20

There are a number of things that can magnetize long slender materials like pipe, rods, etc.

The Earth's magnetic field can induce a residual field in the material if it was shipped in a northerly-southerly direction. The tendency is stronger as you reach the northern or southern latitudes. Likewise, stacking the pipe or rod so that it is aligned in a northerly-southerly direction for a period of time can result in a residual magnetic field. Once again the affect is strongest in the northern and southern latitudes.

Preparing the ends for welding can sometimes induce a residual field in the pipe and the welding of the longitudinal seams may induce a field in the pipe, but in that case the residual field is most likely a circular field.

Carbon and low alloy steels with high carbon equivalencies tend to have lower permeability and tend to be harder to magnetize, but once they are magnetized, they retain the magnetic field more so than softer lower strength steels.

Best regards - Al

By spots

Date 06-10-2009 22:29

Wrap your ground around the pipe several times near the area you are welding.

By Paladin (***)

Date 06-12-2009 03:02

Spots said "Wrap your ground around the pipe several times near the area you are welding."

If that does not do it wrap it the other direction. In other words, if you wraped it clockwise and it did not help, wrap it counter clockwise. Also, I've had luck beating the heck out of drill stem with a hammer. But wrapping the ground usually takes less effort.

By reddoggoose (**)

Date 06-12-2009 13:05 Edited 06-12-2009 13:09

Wrapping DC leads around the pipe may work, and is sometimes done in the pipeline industry but it typically only loweres the magnetism while the DC current passes through the leads, but does not remove it.

Another option would be to try connecting welding leads to each end of the pipe. Then run AC current (start at 100 amps)through it for several minutes. This should break up the polarization of electrons that is causing the magnetism in the pipe. This technique is often used for demagnetizing of welding fixtures that have become magnetized due to the constant unidirectional movement of electrons from DC current, which leaves the electrons in the fixture aligned in a manner that polarizes the fixture.

By 803056

Date 06-12-2009 15:35 Edited 06-12-2009 16:39

If you need to demagnetize the pipe, do a quick search of the Forum using "demagnetize" as your keyword. This subject has been discussed at length and there is some good information presented.

As for demagnetizing the pipe by wrapping the welding lead around the pipe and energizing it with DC, good luck. You'll be back looking for a better method. Do the search for the better answers to your problem and save some time and headaches.

I did the search for you. Here's the thread I had in mind. http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=121249;hl=arc%20blow

Best regards - Al

By Paladin (***)

Date 06-13-2009 01:53 Edited 06-13-2009 17:12

803056,
Read the thread from the link you posted. As always you provide good, interesting, and valuable information. Thanks for your input.

Years ago I often welded on oil field tubing. Sometimes it would be magnetized. Wrapping the lead would work, maybe not completely demagnetizing the pipe but enough to make the weld without trouble. Occasionally I would have to wind the ground lead the opposite way.
Often just moving the ground to the other end would help.

I don't know exactly how it worked, and it may not work according to theory. And it might not work for every situation. But it seemed to work for me. I made the weld. It did not take 30 minutes, just 30 seconds.

By 803056

Date 06-14-2009 16:52

Never argue with success. If it worked for you, that's the way to do it.

Best regards - Al