Tungsten carbide coatings for extreme abrasion resistance

Paul Boughton

Patrice Fournier outlines the benefits of a new generation of tungsten carbide coatings

The oil and gas industry continuously faces dilemmas regarding its operation efficiency. Contractors are more demanding of extreme performance coating materials that offer exceptional performance, reduce plant downtime and increase service intervals - all with constant respect of the environmental constraints.

Deep drilling exploration and oil sand exploitation are two of the more challenging applications which require innovative coating solutions for longer operating times which are under more severe abrasive and corrosive environments and at higher pressures than regular drilling.[Page Break]

Problems of abrasion

Exploitation techniques often requires separation of the water from oil. During operation, huge problems of abrasion occur thus reducing the life of pipes, elbows, pumps, separators, casings, etc.

Downhole tools for drilling are subject to combined stresses such as abrasion, erosion, impact, corrosion and contact pressure. Because their non-sufficient fracture toughness, the traditional 'commodity' tungsten carbide coatings can't withstand all of these stresses simultaneously.

Constant research and development efforts conducted thermal sprayed coatings and hard-faced overlays to become more and more complex with feature enhancements allowing for more severe operating conditions as well as coating life improvement.

The improvement has been achieved with important innovations by alloying proprietary powders with tungsten carbide/metal powders, nano WC/Co, macro WC and/or superfine WC/Co materials. They are mixed with hard and tough metal matrixes which offer exceptional hardness, abrasion/erosion wear resistance and corrosion resistance - and consequently with improved fracture toughness. These grains can be used as powder or converted into electrodes, flexicords and tungsten carbide ropes. These new materials can be sprayed, PTA cladded or brazed with a flame welding torch.

The Hardkarb flexicord or high velocity thermal spray processes allow to produce high abrasion and erosion resistant WC coating with improved fracture toughness. The metal matrix can be chosen from Cobalt, Cobalt-Chrome, Nickel or Ni-Cr-Mo alloys if petrochemical corrosion is present. The usual thickness of these coatings ranges from 0.3mm to 1mm (0.01-in to 0.04-in).

In regards to hard-facing techniques, versus arc welding, the flame welding (brazing) technique is still the best suited technique to avoid decomposition of WC tungsten carbide and allows to produce tungsten carbides welded overlays that contain the lowest content of brittle W2C phases. The usual thickness of these hard-faced overlays ranges from 1.5mm to 1mm (0.06-in to 0.2-in).The brazed overlays combine abrasion resistance, contact pressure resistance as well as rupture toughness in the final coating.[Page Break]

Thermal spray equipment

Improving the coating materials would only be the halfway to the objective, if equipment improvements have not been made. Traditional coating equipment provides limited effectiveness because it is primarily intended for external surfaces and not internal ones. New thermal spray equipment is available for applying coatings to internal diameters. Thermal spray equipment is capable of applying internal coatings down to ~ 6 inches with expected lengths of up to 12 feet.

With a large emphasis on coating performance, the thermal spray industry accomplishes innovative solutions and contributes to create and bring new and highly differentiated products to the market in a cost-effective and efficient time frame.

Enter √ at www.engineerlive.com/iog

Patrice Fournier is with Saint-Gobain Coating Solutions, Avignon, France. www.coatingsolutions.saint-gobain.com/tufcote.aspx

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