The mining sector has seen some turbulent times of late as the emphasis moves towards cleaner and more renewable power sources. One sector however, that is bucking this trend is Deep Sea Mining which has in fact seen a major boost of investment. The seafloor is rich in precious metals and minerals including Tellurium, which is an element used in solar panels and an estimated $150 trillion worth of Gold.
That is not to say that any deep sea mining projects is without serious challenges. Any mining activity that must operate at depths between 1,000 and 3,000 metres proposes a unique set of engineering and surface engineering challenges; pressure, corrosion, wear and abrasion. A number of protective coatings and metal finishing processes are employed to help extend part life in these extreme environments.
Any sort of cutting tool is always likely to encounter abrasive wear and in a subsea environment corrosion is also a crucial factor in component life. Due to the constant pressure of a harsh seawater environment, metals are affected by anodic action that causes surface pitting of the material and cathodic action which makes hydroxide ions through oxygen reduction to the air. Subsea corrosion is more rapid as the seawater itself turns into a voltaic cell which accelerates the process of corrosion.
Mining / Drilling Equipment
In order to provide enhanced wear and corrosion resistance, thermal sprayed coatings are often used. This technique which takes powdered materials, heats them up and sprays them at extreme velocity creates coatings that are characteristically hard and dense with an extremely low porosity, ensuring that the base metal is sealed off from the harsh subsea environment. Popular materials for subsea applications include Aluminium, Chromium and Tungsten Carbide. Often these components will be further protected through a layer containing either PTFE or Molybdenum Disulphide which will ease the effect of friction on moving parts. For housings and structures 2 part epoxy paint may be used to further protect the parts.
Long riser systems are used to transport precious materials from the seabed to the surface, and as deeper depths are reached, the exposure time is significantly longer. A drilling riser is largely comprised by steel line pipes which are painted for protection. There are however a number of steel and stainless components involved which require additional protection, for many of these lager components where tolerances are not an issue coded welding may be appropriate, but for components such as pins, connectors and guide plates thermal sprayed coatings may be a better option.
There are a great variety of valve designs and associated metal finishing process, but increasingly for metal seats, stems and gates valve manufacturers are using HVOF Coatings, in particular Tungsten Carbide and Stellite 6. These coatings are also suitable to the external surface of ball valves and will greatly enhance the wear and corrosion resistance of these parts. One of the other core reasons behind specifying the use of thermal spray coatings for these harsh subsea environments is that they are additive in nature and can be used to repair or re-spray worn areas. This prevents significant costs savings when compared to replacement and even where subsea valves are expected to have a 25 year lifespan, any enhancement can save literally millions.
Metal finishing processes are limited in extreme environments, and although they can certainly extend component life other factors such as maintenance schedules and material mined will have a big impact. B&B precision offer the full machining and coating of components used in subsea Oil and Gas applications. We can offer a completely outsourced solution including sourcing of material, machining of the part and thermal spray coating.