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The evolution of high velocity thermal spray - IGS

Published by , Editorial Assistant
World Coal,

Back in 1995, high velocity thermal spray (HVTS) was an established technology in a highly controlled shop application environment. It was used for specialised applications in aircraft components, valves and other similar equipment. Users of the technology started to ask whether it could be effectively applied in the field to existing fixed assets in-situ.

Field technology was also present at the time. However, it was a different class of technology. Twin wire arc spray (TWAS) or thermal spray aluminium (TSA) are both low velocity thermal spray technologies that are not able to produce reliable coatings to serve in critical erosion/corrosion environments in fixed assets, such as process vessels, towers, columns or power boilers. The existing HVTS equipment and technology could not be taken into the field effectively or economically.

Solution identified

Around 1995, a handful of engineers addressed that problem and took HVTS technology into the field. It was deployed in the downstream oil and gas industry, originally in South Africa, and in the late 1990s this technology was adopted by multinational energy corporations.

HVTS, also known as the high velocity alloy cladding, has continued to evolve. Atomising the wire in a supersonic gas stream was the first piece of the puzzle. This technical development delivered a surface technology that worked well with commonly used welding materials in high temperature corrosion environments, such as in the coal power sector of the time.

New hurdles

At that stage, IGS was exploring the wider utilisation of the technology into other industry sectors, such as the upstream oil and gas industry. The company soon discovered that using a high velocity process to spray off-the-shelf alloy feedstock materials produced particles that oxidised in flight, creating an applied microstructure with permeability pathways for corrosion. While this was not an issue for high temperature erosion applications, it was a fundamental problem for environments with corrosive media e.g. chlorine or sulfur, among other corrosive substances.

Material development

Significant work was then undertaken by IGS in the early 2000s into researching and developing new HVTS feedstock materials, which would control the alloy integrity during the application process. This way the applied microstructure would be fit for the service environment of the asset. The project focused on the permeability of the applied HVTS microstructures, assessing the resistance of the applied materials to permeation by aggressive/corrosive fluids, the shape of the deposited particles being sprayed and controlling residual stresses.

Following development of bespoke feedstock alloys, HVTS would no longer be a shop-only solution when long-term reliability was needed. It has now become a surface technology that could be effectively deployed as a lasting corrosion barrier in the field, during shutdowns and turnarounds, reducing critical path and ensuring lasting reliability in the most arduous operating environments.

Technology Changes

As the adaptation of this technology continued to grow, oil and gas (both upstream and downstream), petrochemical, biomass and waste to energy plant operators started to recognise it as an optimum erosion/corrosion barrier to protect their fixed assets’ parent metal.

Lab vs field

Another important step was to design the application equipment in such a way that “an appropriate corrosion barrier” could be produced in a field environment. For assets such as process vessels, towers and columns, organic coatings started to gain acceptance, but the results were varied and, at times, inconsistent. Complex curing mechanisms, strict application procedures and propensity to mechanical damage made operators look for more reliable, robust, longer lasting solutions, while avoiding the costs and time typically associated with in-situ weld metal overlay. To minimise turnaround time and extend asset life, upstream and downstream operators adopted the HVTS technology, successfully deployed across the globe.

Still developing

The development of this technology is still ongoing, especially in new areas, such as the waste to energy and petrochemical markets. Developing new processes, experimenting with new sources of fuel and utilising waste as a fuel source are important next steps in our global sustainability movement. However, new materials and technologies present a unique challenge for designers and operators in terms of unexpected and accelerated erosion/corrosion. Proven and robust surface protection solutions, which can be deployed in the field within turnaround schedules, are therefore seen as a welcome alternative to repeated equipment replacement.

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