Additive manufacturing extends sensor life

| Manufacturing

Direct metal deposition protects sensors

Andy Pye discovers a technique from OR Lasertechnologie that uses additive manufacturing to provide reliable sensor protection.

An additive manufacturing technique called Direct Metal Deposition (DMD) developed by OR Lasertechnologie in Germany enables reliable protection of sensor elements by means of a hard alloy. It makes it possible to significantly extend the sensor lifetime, for example in oil and gas pipelines.

Industrial sensors are very sensitive components. They are deployed to monitor temperatures, flow rates and pressure precisely and reliably over long periods of time. In many applications, they are subjected to extreme stresses while doing so.

Each day, about a million barrels of crude oil pass through a pipeline of 1m diameter, the equivalent of 1850 litres/s. Onshore gas pipelines have an extremely high internal pressure (100 bar), which can more than double in offshore pipelines. Sensor elements used for monitoring the flow suffer considerable wear as a result of corrosion and abrasion.

Thanks to an innovative powder nozzle developed by OR Lasertechnologie, powder-based laser cladding (DMD) can be used to greatly prolong the life expectancy of these sensors. Since founding the company in 1997, Yhushua Resnik and Uri Resnik have developed new applications for lasers in materials processing and innovative laser technologies for companies including Siemens, Bosch and General Electric. Market sectors include automotive, aerospace, mechanical engineering, electrical, medical, plastics and toolmaking.

The compact EVO Mobile laser welding system is suitable for applying wear-resistant coatings and carrying out repairs or modifications. The system uses relatively low laser output levels starting at 200W, but its high deposition rate of up to 5000mm³/h makes it attractive for a vast range of applications.

One way to protect a sensor from wear is to coat it with Stellite. These cobalt-chromium alloys are very difficult to machine. The conventional approach is to apply composite clad layers with a total thickness of several millimetres. However, the intense heat applied during the process results in considerable mixing of the sensor material with the Stellite cladding. Use of the conventional method therefore considerably shortens its lifetime.

Unlike conventional methods, a laser only minimally melts the surface of the sensor, and only at selected points. Metallic powder, with grain sizes between 45 and 90µm, is fed coaxially to the laser beam and permanently fuses with the substrate surface. The advantages of this approach include precise deposition of the material, low heat penetration and an undistorted, crack-free coating. Track widths of between 200µm and 2mm are possible.

The coaxial arrangement also permits deposition of material independently of the direction of cladding, so that the workpiece can be freely rotated in all directions and, if required, even “grow” in three dimensions. Moreover, the laser parameters can be dynamically adjusted on the fly to accommodate changing conditions.

In order to prevent oxidation and the formation of tiny bubbles, the work is done in a shielding atmosphere of argon, a noble gas. The resulting surface quality is like new, free of pores and cracks, very close to the required final contours, and neat. The sensor itself is hardly affected by this “minimally invasive” technique, while its resistance to wear is greatly improved.

The OR LASER R&D team spent a year collaborating with the Fraunhofer Institute to develop a highly efficient, easy-to-install powder nozzle that works with high repeatability and is suitable for automated processes. “We have found a way to increase the durability of these sensors with our additive laser technique and thus improve the reliability of gas and oil pipelines,” says head of department Markus Wolf.

The system is manufactured in Germany and the nozzle is the first of its kind to enable a combination of wire- and powder-based laser cladding.

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About Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.

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