Revamps 2026 Issue

low application rates and introduces thermal input to the substrate, which may require additional process controls depending on equipment geometry and material condition. Thermal spray technologies have been used for several decades as a method of applying CRA materials without significant heat input to the substrate. However, earlier- generation systems were often associated with coat - ing porosity, oxide formation, and variability in adhesion strength, which could affect long-term corrosion perfor- mance in high-temperature environments. Advancements in process control and material design have led to the devel - opment of improved technologies, which address many of these limitations (see Table 1 ). Alloy cladding technology HVTS alloy cladding is an advanced thermal spray process designed to produce dense, low-permeability claddings suita- ble for corrosion and erosion environments (see Figure 1 ). The resulting cladding exhibits a dense lamellar microstructure with limited interconnected porosity, which is a key factor in reducing permeability pathways. Key characteristics include: • Supersonic particle velocity (≥ Mach 1), enabling dense particle compaction. • Engineered alloy feedstock optimised for thermal spray application.

Typical characteristics of coating technologies

Property

HVTS

Conventional thermal spray

Bond strength

>50 MPa

15-35 MPa

Porosity

<0.5%

2-8%

Particle velocity Microstructure

~1200 m/s

200-250 m/s More porous

Dense

Table 1

Unlike welding-based methods, alloy cladding technol- ogy introduces minimal heat to the substrate and does not require PWHT. As a result, it is particularly suited to appli- cations where: • Shutdown duration is limited. • Thermal distortion must be avoided. • Complex geometries or confined spaces are present. Alloy cladding is typically applied as a corrosion-resistant barrier rather than a structural repair method. It is therefore most effective when used prior to significant wall loss or where structural integrity remains within acceptable limits. The selection of an appropriate repair or mitigation method depends on multiple factors, including: • Extent of wall thickness loss and structural requirements. • Operating environment (temperature, chemistry, erosion conditions). • Available shutdown duration.

• Reduced oxide formation during deposition. • High adhesion strength (typically 30-60 MPa).

Figure 1 Evolution of thermal spray coating microstructure (top to bottom photos), illustrating the transition from conven - tional, porous coatings to dense, low-permeability structures achieved with advanced processes such as HVTS

Revamps 2026