Power Plant FAC Inspection Protocol

Power Plant FAC Inspection Protocol — Niton XL5 Plus XRF Analyzer: Expert Summary

Significance of the topic

Flow accelerated corrosion (FAC) is a critical degradation mechanism in carbon and low-alloy steel piping in fossil and nuclear power plants. FAC causes dissolution of protective oxide layers under flowing, low-oxygen water/steam conditions, leading to wall thinning, leaks and potentially catastrophic failures. Effective, timely detection of material susceptibility (notably low levels of alloying elements such as chromium, copper and molybdenum) is therefore essential for plant safety, reliability and inspection planning. Handheld X-ray fluorescence (XRF) offers a field-capable route to rapidly quantify trace alloying content and inform risk-based inspection strategies and predictive models (for example EPRI CHECWORKS).

Objectives and scope of the application note

The document demonstrates the use of the Thermo Scientific Niton XL5 Plus handheld XRF analyzer within a FAC inspection protocol. Primary objectives are to show that the analyzer can: provide accurate, repeatable low-level detection of Cr, Cu and Mo in carbon steel; match laboratory results closely; and offer sufficient performance to support FAC prevention decisions, inspection planning and input to modeling tools.

Key factors influencing FAC (overview)

• Steel composition: trace alloying elements (Cr, Cu, Mo) have the largest influence on FAC susceptibility.
• Water chemistry: temperature, pH at temperature, and dissolved oxygen levels are important variables.
• Hydraulics and geometry: flow velocity, pipe diameter, fittings and upstream influences affect local corrosion rates.

Methodology and sample preparation

Measurements were performed on certified reference standards and representative carbon steel samples following removal of surface contamination. Surface preparation is emphasized: oxidation, paint, oil/grease and other surface films must be removed prior to XRF measurement because these contaminants can bias trace-element results (paint may introduce Ti, Zn, Ca; grease can contain Mo). Data quality objectives determined minimum preparation and measurement time. Typical test conditions included a 15-second total analysis time for repeatability and accuracy assessments; sensitivity can be improved further by increasing measurement duration.

Used Instrumentation

The principal instrument evaluated is the Thermo Scientific Niton XL5 Plus handheld XRF analyzer. Relevant technical and practical features include:

• Compact handheld form factor, small spot analysis and integrated camera for accurate positioning and documentation.
• High-performance 5 W X-ray tube and silicon drift detector (SDD) for enhanced sensitivity to light/trace elements.
• Optimized geometry and software for low detection limits and fast analysis times.
• Rugged, splashproof and dustproof housing for field use in power plant environments.
• Customizable user interface and workflow to suit FAC inspection procedures and data export for modeling tools.

Main results and discussion

Accuracy and repeatability tests on carbon-steel standards focused on Cr, Cu and Mo at low concentrations. Key findings:

• Excellent agreement with laboratory reference values: chromium results showed a correlation coefficient (R2) > 0.99 versus certified lab data.
• Measured averages (15 s analysis) were close to reference values (example averages from the test set: Cr ~0.077% vs reference 0.079%; Cu ~0.051% vs 0.050%; Mo ~0.0044% vs 0.0047%).
• Standard deviations were small (Cr SD ~0.004% absolute; Cu SD ~0.004% absolute; Mo SD ~0.0005% absolute), indicating good repeatability at the tested levels and measurement time.
• The analyzer reliably detected chromium down to ~0.01% under appropriate preparation and measurement conditions; longer measurement time further lowers limits of detection and improves precision.

Benefits and practical application of the method

The handheld XRF workflow delivers practical advantages for FAC programs:

• Rapid in-field screening of piping and components for trace Cr, Cu, Mo content without destructive sampling or lab turnaround time.
• Ability to prioritize inspection resources: pipes with sufficiently high Cr (industry guidance suggests chromium above ~0.1% markedly reduces FAC susceptibility) may be inspected less frequently, while low-alloy sections can be monitored more closely.
• Data can be exported to FAC modeling tools (e.g., CHECWORKS) to improve predictive accuracy and inspection planning.
• Complementary capability to provide full alloy grade identification and broader chemistry data useful for maintenance and replacements.

Limitations and practical considerations

• Surface condition strongly affects XRF accuracy; rigorous cleaning to remove oxides, paint and grease is mandatory for trace-element analysis.
• Handheld XRF detects surface-near composition; results reflect surface and near-surface chemistry rather than bulk material if significant gradients or coatings exist.
• While handheld XRF reaches detection limits useful for FAC tasks, laboratory OES or ICP methods may still be required for regulatory or contractual requirements demanding different sampling or lower uncertainty.

Future trends and potential applications


Advances and likely directions for FAC inspection and handheld XRF use include:

• Lower limits of detection via improved detector electronics, optimized tube settings and longer acquisition times, enabling more confident identification of marginal alloying levels.
• Integration with plant asset-management and predictive-maintenance systems for automated risk scoring and inspection scheduling.
• Robotic or remotely deployed handheld XRF probes to access confined or high-radiation areas without personnel exposure.
• Automated mapping and imaging workflows combining XRF spot data with camera images and GPS/tagging for rapid documentation of large pipe networks.
• Improved combined-data analytics that fuse XRF composition data with process/water chemistry and flow models to refine FAC rate predictions.

Conclusion

The Niton XL5 Plus handheld XRF analyzer delivers accurate, repeatable, field-capable detection of trace chromium, copper and molybdenum in carbon steel relevant to FAC inspection programs. With appropriate surface preparation and suitable measurement times (15 s demonstrated; longer where needed), the device produces results consistent with laboratory references (R2 > 0.99 for chromium) and can reliably detect Cr at ≈0.01% levels. Handheld XRF provides a practical, rapid screening tool to improve inspection prioritization, supply composition data to FAC models, and reduce dependence on destructive sampling or slow laboratory workflows.

References

1. Chexal B., Goyette L.F., Horowitz J.S., Ruscak M. Predicting the Impact of Chromium on Flow Accelerated Corrosion. In: Pressure Vessels and Piping Conference (PVP), Vol. 338. ASME; 1996.
2. Bouchacourt M. (Electricité de France). Observations on chromium substitution, formation of FeCr2O4 oxide versus magnetite, and reduced FAC susceptibility (as cited in the application note).