Seamless Vs Welded Manufacturing

MICC Group is the only company in the World to manufacture using the BICC seamless tube technique.

There are two fundamental production methods for producing MICC cables:

Seamless

One uses a seamless tube of Oxygen Free Copper (OFC) which has copper conductors with pure magnesium oxide, pre-compressed insulation blocks inserted. This assembly is then annealed and drawn through reducing dies in a repeating process to both compact the MgO insulation forming the cable and conductors to the compulsory dimensions required by BS/EN60702.

Welded

The other process is to take a flat copper strip and form this into a tube which is then seam welded along its entire longitudinal length. During the process, conductors are added along with the Magnesium oxide insulation as an injected powder. The cable is then annealed and drawn through dies in a repeated process to form the cable and conductors to the required dimensions of BS EN60702.

Cable Configuration

The copper, as used in the manufacture of Mineral insulated cables has effectively an almost indefinite life span as copper is essentially immune to corrosion. It behaves like a noble metal in most environments because of the naturally protective film (Cu2O) that forms on the metal's surface. However certain containments like Hydrochloric or Uric acids can cause deterioration.  MgO (Magnesium Oxide) used for the dielectric (insulation) inside the copper tube, is also non-organic and does not age or deteriorate over time provided it is hermetically sealed inside the outer copper tube and the cable terminations remain viable. MgO is however naturally hydroscopic and any exposure to any air moisture will result in the deterioration of insulation resistance which can lead to cable failure.

In considering any differences in long term performance between seamless tube design MICC cables and welded seam design MICC cables it is necessary to understand the process of welding. Oxygen Free Copper can be successfully welded under specific conditions with excellent results. It is, however, important to understand that the welding process introduces some additional elements into the seam weld and even if conducted under perfect conditions and with a perfect process, the weld can absorb oxygen from the atmosphere and introduce pinholes resulting in a significant amount of scrap cable during the production and quality control process.

Advantages and Disadvantages

Generally, seam welded MICC cables can be produced in longer continuous lengths which can minimize the need for (MICC) fire rated inline joints. There can also be some cost savings for the manufacturer due to the production process speed although to ensure a perfect seam weld with no porosity or embrittlement requires a highly regulated and controlled production protocol to ensure consistency of the weld along the full length of the cable.

Ambient temperatures, humidity, raw material quality consistency and interruptions to the production process can cause variations in the weld quality. Seam welded MICC cables can show an internal inconstancy of copper sheath thickness along the weld line which can result in some generally small inconsistency in compaction of MgO and conductors during the drawing down process. This can also create issues when applying terminations (pots and seals).

Seamless tube MICC cables have no inconsistency in the metallurgic structure of the tube and no risk of introduced contaminants as there is no welding. This ensures that during drawing down of the tube to BS EN 60702 specifications and dimensions there is full circumferal and longitudinal consistency in the compaction of the MgO insulation and thus no inconsistency in the compaction and elongation of the cable during production.

Furthermore one must consider the underbead of a welded cable. The underbead is made from copper and as such makes the cable heavier in comparison to a seamless tube cable. Not only does this add to shipping costs, but it also makes it more difficult to install. Furthermore, the underbead can prove much more difficult to strip, which again adds to the total installation time.

Conclusion

Whilst a perfectly made welded seam cable can mimic the long term performance of a seamless tube cable, should there be any areas in the full length of the cable seam weld where porosity or brittleness has occurred due to process deviation, process interruption, raw material consistency, MgO contamination of the weld etc., then any pinholes or hairline fissures which have been compressed shut during the drawing and compaction process can open up over time due to the cyclic heating/cooling, expansion/contraction process, allowing air, moisture or contaminants to enter the cable resulting in a deterioration of the MgO insulation resistance. MICC has also heard of large diameter seam welded cables rupturing under severe impact along the seam weld.

For mission-critical applications MICC seamless tube cables provide optimal lifetime security as well as quicker and easier installation. 

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