Careers Nuclear Asset Life Extension
Protect turbine and steam-system components during planned outages
As nuclear plants plan for longer operating lives, asset reliability and maintenance costs have become a growing concern. Corrosion-related damage – particularly flow accelerated corrosion (FAC), wet steam erosion and localized surface damage – can threaten the reliability of turbine and steam-system equipment. Cross-under and extraction piping, turbine casings, split joints and auxiliary vessels may need protection even when the underlying component remains serviceable.
IGS offers High Velocity Thermal Spray (HVTS®) cladding engineered to protect exposed metal on suitable components. Applied in the field without a fusion heat-affected zone, HVTS® can help operators address vulnerable areas within a planned outage. By reducing time in the work area and the scope of replacement work where appropriate, it aligns with ALARA principles.
Understanding degradation risks in nuclear steam systems
Pressurized Water Reactors (PWRs) operate under high pressure (around 2248 psi/ 155 bar ) to prevent water from boiling at high temperatures, allowing the coolant to enter the reactor core at roughly 527°F/ 275°C and exit at 599°F/ 315°C. In this system, water serves a dual role as both coolant, absorbing heat from the nuclear reaction, and moderator, slowing neutrons to maintain the chain reaction. This heated water then transfers its energy to a secondary circuit, producing steam to drive turbines and generate electricity.
While the systems differ, turbine and steam-system components in nuclear plants can face flow accelerated corrosion, wet steam erosion and localized surface damage.
Cross-under and extraction piping, turbine casings, diaphragms and auxiliary vessels can experience different forms of degradation depending on flow conditions, moisture, materials and component geometry. Understanding the mechanism and measuring the remaining metal are essential to deciding whether a component needs replacement, repair or surface protection.
Common degradation mechanisms in nuclear steam systems
1. Flow Accelerated Corrosion (FAC)
This is where the protective oxide layer on carbon steel piping is dissolved and removed by flowing water or wet steam. FAC can occur under both single-phase and two-phase flow conditions. Its rate depends on factors including water chemistry, temperature, material and local flow conditions.
FAC can reduce wall thickness in cross-under and extraction piping, moisture separator reheaters and other susceptible steam-system equipment. Inspection findings and remaining wall thickness help determine whether a component needs repair, replacement or protection of serviceable metal.
2. Wet-steam erosion and impingement
Moisture carried in high-velocity steam can strike exposed surfaces and cause localized metal loss. Turbine casings, diaphragms, bends and turning-vane areas may be affected. This damage can occur alongside FAC, but the erosion mechanism and the condition of each component need to be assessed separately when selecting a protective alloy or repair method.
3. Localized corrosion and pitting
Water boxes, tanks, heat exchangers and other auxiliary equipment can develop localized corrosion where the material and service environment are susceptible. Inspection should establish the extent of damage and confirm that the remaining component meets structural requirements before a surface protection method is considered.
HVTS®: High-Performance Cladding
HVTS® is an advanced thermal spray technology that atomizes alloy wire and accelerates particles in a supersonic gas stream. Purpose-designed alloy chemistry and controlled application parameters help produce a dense barrier with low oxide content and high mechanical bond strength. The alloy and application specification are selected for the component’s service environment.
HVTS® is a non-fusion cladding process, so it creates no fusion heat-affected zone (HAZ). The substrate remains comparatively cool during application, reducing the risk of distortion on large castings and other heat-sensitive components. Where structural build-up is required, IGS can evaluate RapidClad™ automated field welding as part of the repair strategy.
Supporting ALARA Through Targeted Maintenance
By focusing work on accessible areas of degradation and reducing the scope of replacement where appropriate, HVTS® can shorten time spent in the work area and support ALARA (As Low As Reasonably Achievable) principles. The benefit depends on the approved scope and site conditions.
Reduce Outage Time and Improve Radiation Safety
HVTS® cladding offers practical advantages where the remaining component meets structural requirements:
- No preheat or post-weld heat treatment (PWHT) required for the HVTS® application
- No fusion heat-affected zone (HAZ), with reduced distortion risk
- Surface protection can be staged across planned outages
- Cladding can be inspected and locally renewed where required
- No weld dilution into the base metal
The plant’s engineering team must confirm substrate condition, access, service environment and qualification requirements before selecting HVTS®. Structural build-up or a component that does not meet acceptance criteria requires a different repair or replacement decision.
Comparison Table of Corrosion Barrier Technologies (HVTS & WOL)
| Feature | High-Velocity Thermal Spray (HVTS) | Weld Overlay (WOL) |
|---|---|---|
| Corrosion Resistance | Yes | Yes |
| Erosion Resistance | Yes | Medium (depending on alloy) |
| Typical Alloys Utilized | Modified 625, C-276, Monel | 316, 625, 622, 52, Monel, Hastelloy |
| Bond Type | Micro-mechanical interlocking (MMI) | Metallurgical/chemical |
| Typical Thickness | ~20 mils | 5–7 mm (≈200–275 mils) |
| PWHT Requirement | No | Sometimes required |
| Dilution into Base Metal | No | Yes |
| Heat-Affected Zone (HAZ) | None | Yes |
| Stress/Distortion | None | Possible on thin components |
| Application Speed | Medium-Fast | Slow |
| Repairability | Localized, simple | Complex (grind and reweld) |
| Thermal Resistance | >932°F / >500°C | >932°F / >500°C |
| Curing Requirements | None | None |
Proven Nuclear Applications and Long-Term Performance
IGS HVTS cladding has been proven under harsh nuclear conditions, including:
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Operating pressures up to 2,500 psi (17.2 MPa)
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Temperatures exceeding 572°F (300°C)
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Chemically aggressive service environments with chloride excursions and oxygen ingress
Key test results include:
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No pitting or crevice formation after 10,000-hour immersion
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Minimal mass loss in ASTM G48 and G28 corrosion tests
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Proven protection for 15+ years in multi-industry deployments
“We’re delivering proven, field-qualified cladding solutions that align with ALARA principles while significantly reducing outage durations and lifecycle maintenance costs.”
Keith Reeser, Senior Director of Business Development at IGS
I’m here to help
Keith Reeser
IGS Subject Matter Expert
HVTS® for Planned Outages and Long-Term Asset Protection
HVTS® provides low heat, non-fusion surface protection for selected nuclear turbine and steam-system components. With no fusion heat-affected zone (HAZ) and a reduced risk of distortion, it can help teams protect serviceable metal within a planned outage. The cladding can then be inspected and locally renewed as part of the component’s life-extension program.
Suitability depends on the remaining substrate, degradation mechanism, service environment, access and plant-specific qualification requirements. Where structural build-up is needed, welding or replacement may be the appropriate option.
HVTS Benefits Summary:
- Outage Efficiency: typically 2-3X faster than weld overlay for similar coverage
- Radiation Safety: reduced cumulative worker exposure due to faster application
- Metallurgical Merit: no HAZ, strong bond, minimal dilution, high porosity control
- Durable Protection: proven 15+ years of corrosion/erosion resistance
- Cost Savings: Lower labor and equipment costs, predictable maintenance budgets
Free consultation with an IGS Subject Matter Expert
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