The Evolution of High-Velocity Thermal Spray

High-velocity thermal spray was initially used in specialized shop applications but is now widely deployed in the energy sector for critical equipment protection.
By Marina Silva | January 05, 2020

In 1995, high-velocity thermal spray (HVTS) was an established technology in a highly controlled shop application environment. It was used for specialized 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 or thermal spray aluminum are both low-velocity thermal spray technologies that are not able to produce reliable coatings to serve in critical erosion and corrosion environments in fixed assets such as process vessels, towers, columns or power boilers. The existing HVTS equipment and technology couldn’t be taken into the field effectively or economically.

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

HVTS, also known as the high-velocity alloy cladding, has continued to evolve. Atomizing 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 pulp and paper and coal power sectors of the time.

New Hurdles
At that stage, IGS was exploring the wider utilization of the technology into other industry sectors such as the upstream oil and gas industry. It was soon discovered that spraying off-the-shelf alloy feedstock materials using a high-velocity process produced particles that oxidized in flight, creating an applied microstructure with permeability pathways for corrosion. While this wasn’t 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
IGS undertook significant research and development work in the early 2000s, developing new HVTS feedstock materials that would control alloy integrity during the application process. This way, the applied microstructure would be fit for the service environment of the asset. The R&D project focused on the permeability of the applied HVTS microstructures, assessing the resistance of the applied materials to permeation by aggressive and 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 essential. 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.

Lab vs. Field
Another important piece of the puzzle 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 minimize turnaround time and extend asset life, upstream and downstream operators adopted the HVTS technology, successfully deployed across the globe.

Success Where Others Have Failed
As the adaptation of this technology continued to grow, oil and gas—both upstream and downstream—petrochemical, biomass and waste-to-energy plant operators began to recognize it as an optimum erosion and corrosion barrier to protect their fixed assets’ parent metal. An example at a Swedish biomass power plant illustrates the performance of this solution: The IGS Europe s.r.o. operations team performed a HVTS application in the No. 5 steam boiler at Eon Värme Sverige AB Åbyverket in Örebro, Sweden, during a fall 2017 maintenance period. AP5 is a 170-MW, biomass-fired circulating fluidized bed boiler built in 1988 by Götaverken-Generator, currently Valmet Technologies Inc. In preparation for a future change in fuel composition, Åbyverket wanted to upgrade the existing surface protection system that was previously installed.

The first annual inspection of the IGS HVTS application was conducted in August 2018. The result was as expected; there was no degradation or thickness loss of the applied thermal spray cladding.

Future of High-Velocity Alloy Cladding
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 utilizing waste as a fuel source is an important next step in the global sustainability movement. New materials and technologies, however, present a unique challenge for designers and operators in terms of unexpected and accelerated erosion and 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.

Author: Marina Silva
International Marketing Manager, IGS Inc.