When working with pipes, the demagnetisation process requires that cable is wound around the pipes. Typically 20-50 turns are required. In some situations, such as production and pipe laying environments, the time taken for the winding process can become significant.

The ZMCC has been designed to provide a fast and effective solution for this problem.  In use the Clam Coils are placed around the pipe and the connectors brought together; a cam driven mechanism is used to draw the 25 connectors together in a quick single action.  Now just plug into Zeromag and you’re ready!

Clam Coils are usually deployed in pairs one on either side of the joint as shown in the above picture.

The Clam Coil is available in a variety of formats depending on the application.  It is normally supplied as 25 turns of cable with an array of connectors capable of carrying more than 100A.  The cable connect array has a full wiping action to ensure good clean contact for the 2500A total current through the device.

The forces required to mate and detach the connector array are high, and to make it easy to use, the cable clam has a cam mechanism.  This allows deployment to be carried out in seconds by one person. It is supplied with leads to connect back to Zeromag and storage case.

For Zeromag to null a magnetic field it must first be able to measure it.  The ZM2PG is a robust stainless steel probe designed for the harsh welding environment. The probe plugs into Zeromag and can be zeroed prior to measurement of the field in a the weld prep. In automatic nulling mode it traverses the weld, just ahead of the weld position.  An air (or inert gas) line is connected to the manifold and gas flows through and out of the rear of the probe, away from the weld, to keep the sensor cool.  The ideal gas pressure is 2 bar, a pressure relief valve on the manifold protects the probe from over pressure.

The probe is a key part of  the Zeromag system and, while robust, it can be damaged.  So to avoid project delays keeping a spare probe is recommended.

For larger pipes, or for giving more convenience in positioning of Zeromag,  3m probe extension cables are recommended.

Features of MF300Fm+ Ferrite Meter

• NDT of the ferrite content in a range of 0.1 to 115FN equivalent to 0.1 to 80.5% Fe in austenitic & duplex steel.
• Robust and portable
• Standard or peak measurement of Ferrite Number
• Piecewise estimate of ferrite percentage
• Automatic zero on demand
• Supplied with 5 transfer standards allowing veracity of instrument to be checked
• Storage of 1000 measurements, downloaded to PC with RS232/USB option
• 10mm diameter (P10) and 4x6mm (P46) probe options
• Right angled probe for use where access is restricted (P46R)
• Use with high temperature samples (air-cooled probe option)
• Up to 5 probes per instrument
• Simple measurement with small sample area.
• Units selectable between WRC-FN and %Fe.
• Calibration with standards traceable to NIST standards
• Large character display mode
• Backlit display
• Supplied in carry case

Zeromag is used to eliminate arc blow which can occur when the parts to be welded are magnetic – this shows up as high magnetic field levels in the joint preparation. This table lists the most common effects of magnetism on welding processes.

Even when weak magnetic fields are present in the steel, the effect of the reduction in face area in a V or J weld preparations serves to concentrate the magnetic flux. Consequently, the value in the joint preparation can easily be several hundred gauss and fields reaching 1000 gauss are possible.

Working with large pipes, Zeromag can reduce magnetic field levels to a few gauss even with residual field levels of over 1000 gauss.

With Zeromag, you are in control – you can see the magnetic field level in the weld area, control Zeromag either manually or automatically and see the magnetism shrink to zero.  You then know its clear to weld unimpeded.

Zeromag can be extended to provide joint or pipe end degaussing.

Zeromag controlled by ZM150 degausser is used to degauss pipe joints at fit-up, or pipe ends prior to fit up.  For degaussing to be successful a field must be established that magnetically saturates the steel.  The maximum field achieved for a particular demagnetizing current depends on the pipe diameter (as this determines the number of turns), the wall thickness and the type of steel.  For a standard Zeromag ZM100A joint degaussing is usually possible for pipe diameters to about 16 inches (0.406m).

To increase the degaussing power the dual degausser ZM150x2 provides all of the features of the standard ZM150 but controls two Zeromags.  So the degaussing power is 3kW with two standard ZM100A, 4.5kW with a ZM100A-33 and ZM100A or 6kW with two ZM100A-33.  These higher powers allow joint degaussing on larger pipes and thicker walls.  The table below shows a rough guide to the pipe OD for a particular Zeromag power and wall thickness for achieving 1.5 Tesla in the steel. This is for a standard carbon steel but do note that the degaussing efficacy will depend on the details of the job, in particular the pipe steel, OD, wall thickness and cladding.

Clam coils are recommended for rapid deployment of sufficient demag turns, the number of clams required will depend on the pipe size and degaussing power available, contact Diverse for advice. Clam coils can be connected in series and are available as single wrap (25 turns per clam) or double wrap (50 turns per clam).

A wide range of settings, measurement modes and units can be set by the user through the menu driven user interface.  The operating modes allow magnetic measurements in most industrial and laboratory applications.  Auto zero can be requested at any time by the press of a single key.

Measurements of magnetic fields together with the selected units and a linear progress bar scale are displayed on the instrument.  Operating modes are average, absolute peak, bipolar peak and true RMS.

There is a built-in data logger that can collect 100 samples in the chosen measurement mode and at a selectable rate.  The results can be viewed on screen or optionally downloaded via the serial RS232/USB  interface.  Software for use with the meter is provided with the serial option which enables data to be saved and entered in spreadsheets.

The instrument has 2 other novel features:

• Magnetic test bench mode which provide a simple go no-go indicator for setting up for magnetic particle inspection.
• By inputting the distance for a high current conductor to the probe the instrument can provide a direct reading of the current.   Currents need to be in excess of 1000A.

Zeromag measures and neutralizes magnetic fields which may be present in the weld preparation region of mating steel components.  When welding pipes there are several ways of working. In normal operation, Zeromag is used to dynamically reduce the magnetism during welding.  This works well but having demagnetizing components in place while welding can hinder welding throughout.

The ideal would be to degauss all the components completely, but the process is too long and cumbersome.  There are also issues with penetration of ac degauss fields into the bulk of the material, leaving the core still magnetized.

The Zeromag degauss option undertakes degaussing of the complete fitted up butt joint.  In this mode of operation cable is wound over the pipe butt joint (usually with clam coils) and a quick downcycle initiated.  With the joint degaussed the coils are removed and welding can commence.  Magnetism can return either over time or as a result of the changes in magnetic geometry as welding progresses.  If this occurs the demag procedure can simply be repeated.

The joint degaussing can be extended to pipe end degaussing.  In this mode, the Zeromag degauss option undertakes degaussing of the end of the pipe only prior to fit-up.  This down cycling process is relatively quick – typically less than 3 minutes. The hysteresis loop time is typically 10 seconds allowing deep penetration of the degaussing field into the steell of the pipe end.  The magnetism in the rest of the pipe remains unchanged, so, over time, the magnetism in the rest of the pipe will ‘leak’ back into the pipe end.  This process is material dependent, but is typically about 1 hour.

The dual degausser controller ZM150x2 is available for controlling two Zeromag, this is used for degaussing larger pipes and thicker walled pipes.

Although Zeromag ZM100A can handle all pipes and plates there are some scenarios where the high power version offers important advantages.  These situations are:

• High ambient field environments such as aluminium smelting.  In this case Zeromag has to overcome not only the remenant field but also the ambient field concentrated in the steel component.
• Very large constructions where wrapping long lengths of demagnetizing cable is required. Examples here are large steel frameworks such as are used for oil rig or wind farms.
• Joint degaussing on larger pipes where a higher applied field is required to magnetically saturate the steel.
• Assessment of the magnetic characteristics of pipe steels.  By driving the field to high levels the saturation characteristic can be revealed and the necessary demagnetizing field determined.

The ZM100A-33 retains the same controller as the standard unit and therefore has all the speed and convenience for solving arc blow problems quickly and simply.  As with the whole family of Zeromags, it can be used with the ZM150 degauss unit.  With Zeromag, you are in control – you can see the magnetic field level in the weld area, control Zeromag either manually or automatically and see the magnetism shrink to zero.  You then know its clear to weld unimpeded.

Zeromag ZM100A is used world wide by leading welding companies to overcome arc blow. When working with pipes this process requires demag cable to be wound, typically 20 to 25 turns. Winding can be a slow process typically occurring after fit-up. Split bobbins offer the opportunity to wind the cable off line;  bobbins and cable are then passed over the pipe end prior fit-up. Often these are used one either side of the weld preparation. Eye-bolts on  the bobbin facilitate hoisting of the cable and bobbin assembly.

Once welding is complete cable can be quickly pulled off the bobbin. Thumb nuts are then loosened and the bobbin can be split for removal from the pipe. The process is then repeated for further joints.

Split bobbins are aluminium construction and manufactured to pipe size, specified at time of order.

The kit comprises:

• Zeromag ZM100A demagnetizer
• Air cooled magnetic probe
• Demagnetizing cable 50m
• Magmeter MF300H+ gaussmeter
• Demagnetizing and probe extension cables
• Storage and shipping cases

Other components of the kit include the MF300H+, the tool of choice for measuring in magnetism in weld preparations.  The ZM2PG air cooled probe which is built from stainless steel and is sufficiently robust that it can be used close to active welding in the weld prep.

A full cable set of demagnetizing cables and extension cables is provided. Finally, the whole kit is supplied in 2 robust packing cases for transport and storage.

The DKPW comes with simple and comprehensive instructions for use.  Diverse provide telephone and email support as well as training packages either on-site or on-line.  DKPW is available for hire for short term projects; contact Diverse for current availability.