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High Temperature Hydrogen Attack (HTHA) Detection in Welded Pressure Equipment

Industrial Context Description

HTHA affects carbon steel and low-alloy steel equipment that operates under high temperature (>200°C) and hydrogen partial pressure, such as pressure vessels, piping, nozzles, and welds. These components are commonly found in refineries and petrochemical plants, particularly in hydrotreating and hydrocracking units.

At-risk areas include welds and heat-affected zones, where residual stress and microstructural vulnerability favor the formation of methane-induced microcracks. API 941’s Nelson Curves guide operators in identifying conditions favorable to HTHA and planning mitigation strategies such as routine inspections and materials upgrade.

Industrial Pain-Point

HTHA is difficult to detect, progresses internally, and can cause sudden rupture of critical components. The economic and safety risks are immense:

  • Catastrophic failures (explosions, toxic leaks)
  • Extensive shutdowns
  • Regulatory liabilities

Traditional UT techniques (velocity ratio, backscatter) have major limitations:

  • Poor sensitivity to early-stage damage
  • High false positive rates
  • Inability to quantify depth
  • Operator-dependent interpretation
  • Challenges with dirty steel/inclusions

The industry lacks standardized, high-resolution tools capable of reliably detecting and characterizing HTHA across all stages.

Description of EIG Solution

EKOSCAN INTEGRITY provides a robust inspection suite conforming to the latest API RP 941 (2020) update, integrating:

TOFD (Time-of-Flight Diffraction):

  • Sensitive to early HTHA microcracks
  • Ideal for welds and thinner components
  • Detects diffracted signals from internal defects

PAUT (Phased Array Ultrasonic Testing):

  • Multidirectional imaging in a single scan
  • Supports 64–128 element probes
  • Enables accurate detection and high repeatability
  • Validated by MTI using realistic mockups

TFM (Total Focusing Method):

  • Uses FMC/PWI acquisition for full-depth coverage
  • Enhanced resolution and defect characterization
  • Now standardized in ASME V and ISO 23864/23865

PCI (Phase Coherence Imaging):

  • Ideal for diffuse, omnidirectional microcrack detection
  • Complements TFM with better noise rejection
  • Not yet codified, but highly effective in early-stage HTHA

Equipment & Tools by EKOSCAN:

  • Mockups: CALHTHA-25/50, PATYPE19675A
  • Probes: MTI-validated, optimized PAUT (64/128 element)
  • Scanners: Handscan (1-line), Weldscan (circumferential), Accutrak (automated, modular, steerable)
  • Training: offered by EKOSCAN experts on advanced commercially-available flaw detectors.

Industrial Gains

Early warning capability before catastrophic failures
Reduced false calls and more confident go/no-go decisions
Improved productivity via high-speed full-coverage scanning
Lower training threshold thanks to high-resolution visuals
Data traceability for lifecycle monitoring

Return on investment via

70% reduction in downtime-related losses
Up to 80% improvement in detection reliability
Minimized inspection time and technician hours

Sources

  1. Lozev, M.G., Neau, G.A., Reverdy, F., Lonné, S., Cence, H., et al. Assessment of High-Temperature Hydrogen Attack Using Advanced Ultrasonic Array Techniques. Materials Evaluation, Vol. 78, No. 11, Nov 2020, pp. 1223–1238. DOI: 10.32548/2020.me-04183
  2. Krynicki, J.W. (ExxonMobil). Probabilistic Risk-Based Approach for Performing an Onstream HTHA Inspection. NACE/AMPP Conference Paper, 2006.
  3. Reverdy, F., Wassink, C., Fromentin, O. HTHA Inspection Using Ultrasonic Techniques. Ultrasonic Testing Conference 2021, NDT.net
  4. Bleuze, A., Cence, M., Schwartz, D., Chelminiak, G. On-Stream Inspection for HTHA. ECNDT 2006, NDT.net
  5. Dupont-Marillia, F., Krynicki, J., Belanger, P. Early Detection of HTHA Using FMC and Post-Processing. ResearchGate
  6. Trimborn, N. (Mistras). Detecting and Quantifying HTHA. WCNDT 2016, NDT.net
  7. Nugent, M., Benac, D., Berg, S. (BakerRisk). API RP 586 Inspections for HTHA and API 941 Remaining Life Prediction. BakerRisk White Paper
  8. Inspectioneering Journal. Into the Grain – Advancements in HTHA Detection Methods. Inspectioneering.com
  9. American Petroleum Institute (API). API RP 941 and API RP 586.

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