Wear resistant thermal spray coatings protect ball valves, extend service life

25 July 2018 | Web Article Number: ME201810946

Chemical & Allied Industries
Mining & Quarrying
Motors, Drives & Transmissions
Pumps, Valves, Pipes & Fittings

HIGH Velocity Oxy-Fuel (HVOF) thermal spray process can help to extend the service lifecycle and enhance the performance of metal seated ball valves, improving uptime and productivity for end-users.

That’s according to engineering and coating technology specialist, Thermaspray, which adds that this is particularly relevant for valves used by the chemical, petrochemical and mining sectors.

In such applications, valves are often exposed to corrosive fluids containing wear particles which, when trapped between rotating and stationary surfaces, cause abrasion wear damage.

In addition, the impact of particles with high velocities on exposed surfaces lead to erosion wear damage. This corrosion and wear of critical surfaces degrade the valve’s performance forcing frequent replacement or repair of damaged valve components.

“The subsequent cost implications are further exacerbated by downtime and losses in production,” said Paul Young, Spray Shop Manager at Thermaspray.

Metal seated ball valves are ideal for handling hot, abrasive and corrosive applications and owe their superior performance not only to their unique design but also to quality wear resistant thermal spray coatings.

In the thermal spray process, a coating, most often metal alloy, carbide or ceramic that may vary in thickness, is applied onto a substrate through the projection of a molten stream of the necessary material.

Wear resistant thermal spray coatings protect ball valves, extend service life

According to Young, one of the many advantages of thermal spray technology is the ability to produce carbide-based coatings. These carbides, also known as tungsten carbides (WC) or tungsten combine the hardness of a ceramic with the toughness of a metal.

“Thermal spray coating process applied to the contact surfaces of ball valves and seats has found wide acceptance with end-users. We apply the state-of-the-art HVOF coating process to protect all components of metal seated ball valves.”

Thermaspray supplies coated ball valves which include all components - end caps, ball valve, valve seats and valve shafts - to a longstanding key customer and leading valve manufacturer, stockist and distributor in Kwazulu-Natal, who in turn supplies the end-user with the finished product. According to Young, HVOF coated ball valves can compete and even exceed international products.

HVOF is a flexible dry-coating technology which constitutes two main carbide materials used in thermal spray processes in order to improve wear resistance and decrease coefficient of friction between various sliding components. HVOF exhibits higher densities and superior bond strength (typically greater than 80 MPa) and less decarburisation than many other thermal spray processes - making it possible to produce very dense and hard coatings with excellent coating adhesion.

This, according to Young, is due to the higher particle impact velocities and relatively low peak particle temperatures associated with the HVOF process. “In this process particles actually travel faster than the speed of sound, generating the best bond strengths, density and hardness compared to other thermal spray processes.”

Because spraying parameters like standoff distances and spray angles are fundamental to controlling coating quality and uniformity, robotic manipulation is used for spraying complex components like ball valves. Thermaspray coating processes are applied at Thermaspray’s facility in Olifantsfontein, Johannesburg, using 6-axis robotic gun manipulation. In addition to ball valves, Thermaspray’s capabilities also extend to the coating of new and worn rotary, butterfly and gate valve components.

The local valve sector has been given a much needed boost thanks to the local designation of South Africa’s valves by the Department of Trade and Industry (DTI) as a priority product.

The encouragement of local valve manufacture stimulates industries such as foundries and steel manufacturers as well as the wear coating, hardening, stelliting, chrome carbiding, rubber and allied sectors, bringing numerous benefits such as job creation and skills development.

Thermaspray expects to see good growth in the local valves industry which already makes up a substantial share of the company’s thermal spray coating business.

Thermaspray, in a joint venture with Cape Town-based Surcotec.

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