Overview

At pipe fit-up Zeromag can be used in field nulling mode.  This will solve magnetic arc blow, however, there are welding scenarios where this is limiting.  In these cases, degaussing the joint i.e. removing the field completely , is preferable.  Zeromag with the ZM150 facilitates joint degaussing.

There are a number of scenarios where you may wish to use joint degaussing:

1. You are in a production scenario and have zoned magnetism
2. You are using inconel clad pipes and non-magnetic welding material
3. Operational preference for not having demag equipment deployed while welding

What are the limitations?

To be successful in degaussing steel a field must be established in the steel that is large enough to magnetically saturate the steel.  If this not achieved then field will be left in the pipe ends at the end of the degauss cycle.

Geometry and material properties are important in controlling the magnitude of the required applied field.  The rule is smaller pipes and thinner walls are more likely to be successful than larger pipes and thicker walls.

Zeromag ZM100A supplies up to 100A through 100m of cable.  Our highest power Zeromag is the ZM100A-33, this supplies up to 100A through 200m of demag cable.

Diverse can model particular pipe  geometries and provide advice on whether a partuicular job is likely to be successful with joint degauss.  Remember, field nulling is always there as a back-up solution.

Recommended equipment

Recommended is Zeromag (standard or high power), ZM150 degausser, clam coils for your set-up.  Although you can wind the cable supplied with the Zeromag this is not efficient and clam coils are strongly recommended.   With this technique, field is removed from the joint but remains in the rest of the pipe.  Over time (hours) this magnetism will leak back into the joint.  With clam coils joint degauss is a quick process and welding can begin within a few minutes of completing the degauss.  If magnetism does reappear in the joint later in the job then joint degauss can be repeated, with minimum disruption to the welding.

Good practice

It is good practice to use the maximum length of cable that Zeromag can drive. For ZM100A this is 100m or for ZM100-33 it is 200m.  It is recommended to use clam coils, although these will not give exactly 100m.  With clam coils keep adding them until the total length used is great than 100m. This will ensure the highest field is applied and give the best opportunity to magnetically saturate the material.  Note with more than 100m of cable the maximum current ZM100A will apply will be less then 100A, this is OK.

Ensure the degauss turns are kept as close to the weld region as practical, although deployment up to 1m from the weld prep is often effective.

If having adjusted the rate and percentage reduction the field is not reduced sufficiently then the material is not being magnetically saturated and ZM100-33 is recommended.

This option provides for a quicker method for demagnetizing than downcycling.  In order to use it the ZM150 has to use the material learn facility which finds the optmal single cycle parameters.  If using this option it is recommended that downcycling is used first to check that degaussing is successful for this particular job.

Once the joint has been degaussed the clam coils (or cable) are removed and welding progresses . If the weld material is steel then it is unlikely that any further degaussing will be required.  On jobs where the pipe is steel with inconel lining often the fill material inconel the weld is not magnetic.  This means that the steel may become magnetised again, either from the weld current ior leaking back from the rest of the pipe. In this case joint degaussing may need to be repeated at one or more points through the job. On such jobs clam coils are highly recommended for their speed of deployment.