Valve World Magazine August 2025 | Page 23

Severe service

Table 1: Field performance benchmarking of legacy coating technologies.

QtyX, Appl.( NPS, Cl.)

Time in service( months)

Number of cycles

Common failure mode

3X heater feed pump( 10, 150)

12X feed pump suction( 10, 300)

12X feed pump discharge( 10, 300)

30-36 > 500

30-36 > 500

12-24 > 500

Some components exhibited coating delamination, while others were cleaned and returned to service

6X autoclave discharge( 14, 600)

≤ 6 ~ 50

Coating delamination and erosion on the ball and seat surfaces confirming the strength of the platform and underscoring the need for continued coating innovation.

In-service coating limitations

Over the last two decades, improvements in valve design and metallurgy have advanced equipment performance in hydrometallurgy. However, coating durability remains a key limitation, particularly in the most aggressive service zones. While some valves last up to 36 months, those in discharge lines often fail in 6 months or less due to:

• Cracking and spallation, especially in high impact, thermally cycled zones

• Delamination, exposing base materials to direct slurry attack

• Erosion and thinning, leading to leakage and eventual valve failure

These degradation modes highlight the need for a more advanced coating solution that delivers not only corrosion and wear resistance, but also mechanical toughness.

Evolution of coating technology in hydrometallurgy

Coating development has evolved to meet the increasing demands of HPAL and POx operations( see Table 2). Initial efforts in the 1990s relied on chromium oxide( Cr2O3) coatings. While effective in POx, they lacked corrosion resistance for HPAL and degraded prematurely. By 1998, titanium dioxide( TiO2) coatings emerged as a more corrosion-resistant alternative. However, they fell short in abrasive slurry environments due to limited wear resistance. In 2006, Velan introduced a Cr2O3 – TiO2 composite, designed to balance wear and corrosion protection. While more robust, the system still faced issues with crack propagation and long-term durability. Recognising this gap, Velan launched a dedicated R & D programme to develop a next-generation coating— VEL-8.

Conclusion

Despite notable advancements over the past two decades, legacy coatings continue to fall short when exposed to the most aggressive service zones in hydrometallurgical operations. Challenges such as delamination, erosion and cracking persist, particularly in highimpact, high-temperature, and corrosive environments like autoclave discharge lines. These recurring limitations have highlighted the need for a more robust and reliable surface protection solution that can withstand the combined demands of corrosion, wear and mechanical stress. Recognising this critical gap, Velan launched a focused research and development initiative aimed at redefining coating performance under extreme process conditions. This effort led to the creation of VEL-8, a next-generation coating engineered to deliver enhanced durability, crack resistance, and long-term reliability. The development journey and performance highlights of VEL-8 will be detailed in Part 2 of this article.

What will follow in part two

In part two, Fadila Khelfaoui and Luc Vernhes will introduce VEL-8, a next-generation ceramic coating engineered for the harshest hydrometallurgical environments. They will explore its unique formulation, advanced application process and superior lab and field performance. From extended wear life to enhanced crack resistance, VEL-8 sets a new benchmark for reliability in HPAL and POx operations.

Table 2: Historical progression of coating solutions in hydrometallurgy. 1995 1998 2006 2018 2019-2020 2021

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