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NewsZeroZone - Zeromag zone accessory

When working with plate or pipes, the demagnetisationprocess requires that the magnetic field is controlled via the demagnetising cables. This works well whenthe object can be coiled around with the cables but for

large diameters or plate applications lay on coils are used.

For high fields the most efficient way to null the magnetic field isto use ZeroZone. This is pre-wound with 40 turns and provides amagnetic bridge across the weld prep to allow control of themagnetism.

In operation, ZeroZone is placed across the weld prep. The armsand pole pieces are adjusted so that the active area of the polepieces are in close contact with both sides of the work piece.ZeroZone is then connected back to Zeromag and the systempowered on. All the normal modes of Zeromag are available.

Once the magnetism is nulled, welding can commence within thejaws of ZeroZone, and as the weld advances, ZeroZone can be moved to track the torch or welding halted to allowZeroZone to be moved. The technique used depends on the application. See sub-sea article for under water application.

Recently, Diverse have supplied Zeromag systemsto a number of aluminium smelters around theworld. These have be used to repair steelwork in

the smelter plant that has become magnetized by the

induced magnetic field arising from the very high bar barcurrents, typically 400KA.

In one case we provided the required product support byguiding the customer’s team via Skype meetings. Thisallowed for truly interactive assistance for very low cost.

In another case one of our team was seconded on-sitewith the customer and worked with the team to completea complex welding job. This involved removing magneticfields of over 800 Gauss working several meters up on thecrane gantry.

Zeromag is an excellent tool for removing magnetisminduced in steel parts in smelters. Its highly efficient DCfield operation means that it is able to null high fields thatcould never be addressed by AC demagnetisers.

Diverse worked with Rio Tinto on ZeroB, a system toallow welding on busbars. Trial work was carried out in anumber of smelters, and it was found that ZeroB workedvery well for repairs to bus bars where the field waspredictable and the weld pool was not bridging highcurrents. A very successful project was carried out on asmelter in Bahrain to repair cracks in the power supplybusbars.

We continue to have an interest in welding busbars insmelters and would be pleased to discuss specificapplications with interested smelters.

DIVERSE

ZEROMAG

The standard Zeromag ZM100A has over the years been usedin many different industrial applications from pipes to platesfrom China to America. Although not hyperbaric, it has been

used in habitats sub-sea. At the request of a customer who is aleading sub-sea operator, Diverse have developed a version ofZeromag, the ZM50, designed specifically for sub-sea operation.This new version of Zeromag is to be integrated into the structureof the habitat vessel.

The new unit is completely reformatted and redesigned to allow itto be packaged in a cylinder which can be sealed in one of theworking pods of the sub-sea habitat. The unit is constructed usingstainless steel and even with this steel construction the weight hasbeen kept to a reasonable 30Kg.

For this customer speed was of the essence and the time taken tocomplete the new design and manufacture the first unit was only 10 weeks. The work included new packaging, systems

modelling, design and manufacture all completed on schedule.Although we were able to take advantage of some of the designideas in the standard product, major changes were required inthe controller, power unit and packaging.

The ZM50 is supplied as standard with either 50A operating or,with the addition of a second power unit, this can be boosted to100A matching the performance of the standard Zeromag.

Underwater welding in the wet has made it possible to repairunderwater heavy structures such as oil rigs, pipelines and shipplate that cannot be transported to land, to weld in air. This is adifficult process because of low visibility for the welder to seewhat he is doing and, during the process, the arc and base metalare surrounded by water that can result in quenching of hot

material resulting in poor mechanical weld strength and porosity. All the usual problems of magnetism remain andindeed, because these structures have often been left in a single orientation over extended periods, the ferrous partsbecome can become highly magnetised by theearth’s magnetic field.

As discussed in our leading article, ZeroZone is nowavailable and this too can be used sub-sea - withwet welding. In this case the Zeromag is sitedtopside and ZeroZone and the Zeromag probe usedby the diver in the water. Its operation in this moderequires some small changes to the standard setup:the connectors to the cables to Zeromag need to besealed from the water (this can be done with asimple grease on the electrical parts and sealingtape); a special version of the Zeromag probe isrequired sealed for subsea operation. With thisarrangement ZeroZone can be used at depths of upto 40m (130 feet).

Zeromag goes subsea www.diverse-technologies.net

Zeromag is a general purpose tool that can be usedto null magnetic field or degauss components toallow zero magnetic field and uninterrupted

welding.

With such a versatile tool,there are many differentways of conducting anyjob, and Diverse areroutinely called to solvearc blow problems aroundthe world. This notedescribes the methodologyused:

Firstly there is a need tounderstand the magnitudeof problem and to do thiswe use the Magmeter to doa magnetic site survey.Taking readings in the weld prep gives a good idea of themagnitude of the problem, but by also taking readings oncomponents before fit up allows you to identify which onehas the magnetism problem.

Remember that the field reading that you get at the edgeof a component is the field in air - in the material the fieldwill be several hundred times higher - so a net reading of3 gauss in air may indicate a field of several hundredgauss in the component. (Diverse have an instrumentthat allows measurement of the field in the material, theMF300B+).

Knowing which component has the high field allowsdeployment of Zeromag preferentially on the magnetizedpart.

Next we need to decide how to deploy the demagnetisingcables. For pipe butt welds there is the choice of coilsone side or the other or both. We have found that themost efficient deployment is to have coils on both sides.However there are scenarios where deployment on oneside is preferred: for tie-Ins and seabed oil christmas treesthe best place for the coils is on the pipe side.

The demagnetising coils can be placed some distanceaway from the weld prep. - typically 0.5m back from theweld prep This is because the magnetic flux stayspreferentially in the steel components. This has theadvantage that minimal weld splatter falls on the cables.

The next part of the process is to decide which techniqueto use to defeat the magnetism. Using Zeromag manualmode and adjusting the demagnetising current to null thefield is always successful and is simple. It is always a

good starting point! Onceyou know that this worksthen auto mode can be used.In production setups withrobot welders it is usual to fixthe Zeromag probe to abracket on the torch carrierwith the probe running about50mm ahead of the weldposition. In this way theprobe is kept in the rightposition relative to the torch.Remember if the probe isused near the arc or onpreheated pipes then the

probe must be used with the pressurised air or inert gasfeed to keep the sensor cool.

Joint and pipe end degauss is another popular pipeapplication, requiring the clam coil and ZM150 Zeromagoptions. Using 2, 25 way clam coils on either side of theweld prep or over the joint, the zone where welding is tobe conducted can be degaussed (removing themagnetism) such that once completed the equipmentcan be simply disconnected and welding conductedwithout Zeromag in place. If the magnetism returns thenthe process can be repeated.

Working with butt joints of construction beams is verysimilar to pipes with the demagnetising coils wrappedaround the component parts. However there are projectswhere the component parts are too large fordemagnetising coil wrapping, for example ship plate orLPG tanks. In this case there are 2 options, lay on coils orZeroZone (see page 1). Lay on coils are deployed aslozenge shaped coils either side of the weld prep but inthis case the coils need to be quite close to the weld line,say 50mm and will therefore need some protection.Additionally this is magnetically not so efficient so expectto need to run at rather higher currents for field nulling.

We hope that you found some of the points in this shortapplication note helpful; we are always pleased todiscuss specific jobs and applications with Zeromagusers.

ZEROMAGwww.diverse-technologies.net

ZEROMAGwww.diverse-technologies.net

DIVERSE own the copyright and patents of its products which are continuously under development. We reserve the right to change product specifications without notice.

User calibration has been just one of a number ofrecent improvements and updates to theMF300Fe+ ferrite meter.

The ferrite level is important to assure minimum exposureto solidification cracking when depositing austeniticstainless steel weld metal. A lower ferrite number is betterfor corrosion resistance, while balancing higher ferritecontent to avoid solidification cracking in the weld deposit.Low ferrite numbers are less important for applicationssuch as cladding where no cracking is observed. Testingfor ferrite number can be achieved using the MF300Fe+and crack testing can be done using liquid penetrationverification.

An important update to the Diverse Ferrite meter is theuser calibration mode. The concept of user calibration isthat small changes in the scale calibration of the instrumentcan be trimmed by the user using one of the suppliedtransfer standards. This technique provides confidence inthe performance of the instrument and maximises the timebetween repeat factory calibrations. For example, overtime wear occurs where the ferrite meter probe is broughtinto contact with the sample. This causes small changesin the magnetic response of the probe. This effect can bemitigated with a user calibration on the ‘T0’ transferstandard: one of the 5 transfer calibration samples suppliedwith the instrument.

Following requests from our users we have extended thememory storage facilities in the new MF300Fe+. Thenumber of records is significantly increased to 1000(previously 52), and with each record is stored a useridentification (ID) along with the record number. Thisallows either identification of measurements taken in thefield, or IDs can be downloaded direct to the MF300Fe+for the user to use during data collection. The useridentification is a four character field with characters fromthe ranges 0-9 and A-Z and space.

The PC software to communicate with the instrument hasbeen enhanced to include the extended memory and IDs.With the larger memory communications speeds havebeen doubled to allow swift uploads and downloads.

These new facilities allow different ways of working withthe Ferrite meter, most notably the IDs which can be usedto identify measurement sites or a combination of sites .One application is repeated measurements at the samemeasurement site, e.g. if the site ID is “ABC”, then ABC0,ABC1 … ABC9 could be used to identify 10 samples takenat the same point. Once this data is downloaded a simplespreadsheet application can be used to evaluate the meanand standard deviation of that site measurements.

This extended records feature ensures that a days worthof site surveying can be undertaken without the need toreturn to the office to download results.

DIVERSEZeromag House,

46-48 Whittlesford Road, Shelford,Cambridge, UK CB22 5EWTel: +44 (0)1223 84 44 44

Sales@diverse-technologies.net

Ferrite meter updates - extended memory & user calibration