Stainless precision steel strip for demanding welding processes used in the production of shielding tubes for optical fibers in deep-sea cables

A global network of high-performance submarine cables forms the backbone of our digitally interconnected world. The core of these digital lifelines consists of sensitive optical fibers that transmit large amounts of data at top speeds over long distances using optical signals. Waelzholz supplies a special stainless precision steel strip for the manufacture of the heavy-duty tubes used to shield the optical fibers inside these submarine cables. This material not only reliably meets the stringent requirements for precisely defined material properties over numerous delivery batches, but also simultaneously possesses the weldability and forming properties relevant to the complex production process.

Even though satellites are increasingly being used particularly to connect remote regions to the global digital data network, leading digital corporations such as Google and Facebook are pushing ahead to expand the network of submarine cables based on optical fibers that span the globe. This is because only these can reliably transport the immense quantities of data generated by digital communication around the world at high speed. Today, over 400 submarine cables already carry well over 90% of the digital data traffic between the continents, and the figure is rising.

A map of the network on the website www.submarinecablemap.com shows the impressive extent to which these cables connect our world.

In theory, the speed at which data packets from an American website, for example, reach a destination in Europe via one of the transatlantic fiber-optic cables is no faster than via a conventional copper cable. In both cases, the transmission time is less than one hundredth of a second, which is shorter than the time it takes to blink an eye.

Fiberglass cables offer significant advantages in terms of signal quality even over very long distances, while at the same time making much higher frequencies and therefore significantly higher bandwidths possible. In addition, electromagnetic interference has no effect on signal transmission via fiber-optic cables.

To ensure that the billion-dollar investments laid in the deep sea are protected in the best possible way and that data transmission through the fine optical fibers functions reliably, the high-tech cables, which appear unremarkable from the outside, must comprehensively protect their sensitive core. For this purpose, the manufacturers rely on a system of different types of layers in order to protect the optical fibers inside the cable as effectively as possible from the various stresses during installation and during their long-term use many thousands of meters below the surface of the water. (see Figure 1).

To create and protect the functional core of the cable with its sensitive optical fibers, cable manufacturers rely on our special stainless steel. According to Ralf Sauer, sales specialist at Waelzholz, “the sensitive optical fibers are embedded in a special gel in the shielding tube made of our stainless precision steel strip (see Figure 2). The steel tube not only serves to protect as well as seal the cable throughout its life on the seabed, but also to protect the fiber-optic strands during subsequent production processes, such as sheathing with additional layers, as well as the final laying of the submarine cables.”

When processing cold rolled steel strip into tubes, the ability to form the material used plays an important role. Stainless precision steel strip from Waelzholz ensures that this is the case thanks to exactly defined mechanical material properties. The microstructure, including the grain size, is the key factor in this respect, as it ensures that the material properties remain constant over the entire strip length and over many production batches. The ideal ratio of alloying constituents, the selective adjustment of the microstructure, and a high degree of dimensional tolerance ensure that the material offers the maximum level of formability for the customer.

“Our customers perform several complex operations when manufacturing the cable core. They first form the stainless precision steel strip into tubes and sheathe the optical fibers with them. Then the cutting edges of the tubes are welded together with high precision. In a last stage of the process, the remaining gaps are filled with gel. This high-precision process of manufacturing the kilometer-long cables must be completely smooth without any issues,” reports Waelzholz materials engineer Jan Ullosat.

Waelzholz achieves the dimensional tolerance of the steel strip used, which plays a vital role in the uniform circumference of the shielding tubes, by means of extremely precise slitting processes in which the width of the steel strip is accurately matched to the desired circumference of the subsequent tube.

Highly uniform cutting edges are a fundamental requirement for exact and symmetrical weld seams on the shielding tubes. An absolutely constant cutting profile provides the perfect baseline condition for welding the edges of the strip. With the help of special tools used during the cutting process, Waelzholz achieves perfect edge quality with very little burr formation. In order to further improve weldability, Waelzholz uses a material specially adapted to the application. The completely grease-free surfaces also improve the subsequent weldability of the material.

“Because it offers an unsurpassed level of workability and reliable material properties, our stainless precision steel strip is our customers’ first choice for the core of this demanding application. The consistently flawless product quality results in reliable and interference-free data transmission through the optical fibers in the submarine cables sheathed with materials from Waelzholz,” sums up materials specialist Ullosat.