Industrial sensors are very sensitive components. They are deployed to precisely and reliably monitor temperatures, flow rates, and pressure over long periods of time, and are subjected to extreme stresses while doing so. Each day, about a million barrels of crude oil, or 160,000m3, pass through a pipeline with a diameter of 1m. That is equivalent to 1,850l/s. Onshore gas pipelines have an internal pressure of 100 bar, offshore pipelines can often reach 200bar. Sensor elements used to monitor the flow suffer considerable wear as a result of corrosion and abrasion. This shortens their lifetimes and necessitates costly repairs.
OR LASER’s compact EVO Mobile laser welding system is suited for applying wear-resistant coatings and carrying out repairs or modifications. The system uses relatively low laser output levels starting at 200W, but has a deposition rate of up to 5000mm³/h making it ideal for a range of applications.
The way to lastingly protect a sensor from wear is to coat it with Stellite, a cobalt-chromium-based alloy that is said to be 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 mingling of the sensor’s material with the Stellite cladding.
Unlike with conventional methods, the laser minimally melts the surface of the sensor, and only at scattered points. Metallic powder, with grain sizes between 45 and 90µm, is fed coaxially to the laser beam and permanently fuses with the object’s surface. The advantages of this approach include precise deposition of the material, low heat penetration, and an undistorted, crack-free coating.
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, ‘grow’ in three dimensions. Moreover, the laser parameters can be dynamically adjusted to changing conditions on the fly.
In order to prevent oxidation and the formation of bubbles, the work is done in a shielding atmosphere of argon. The resulting surface quality is claimed to be free of pores and cracks and close to the required final contours. The sensor itself is said to be hardly affected by this ‘minimally invasive’ technique, while its resistance to wear is greatly improved.
“We’re proud of having 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,” said Markus Wolf, head of the R&D department at OR LASER.
OR LASER not only develops laser welding and cladding systems, but also the means of controlling them. For example, the CAD/CAM software solution, ORLAS SUITE, is said to be able to program the cladding strategy for complex geometries and align the required laser tracks with micron accuracy.