High Temperature Hydrogen Attack (HTHA)

🔹 Overview

High Temperature Hydrogen Attack (HTHA) is a critical damage mechanism observed in carbon and low-alloy steels operating in hydrogen-rich environments at elevated temperatures, typically 200°C and above.
At TCR Engineering & Services, advanced HTHA inspection and assessment techniques are used to detect, characterize, and evaluate hydrogen-related damage in pressure equipment.

🔹 What Is High Temperature Hydrogen Attack (HTHA)

At high temperatures, atomic hydrogen diffuses into steel and reacts with carbon present in the material, forming methane (CH₄) as per the reaction:

MC + 4H → M + CH₄

The methane molecules cannot diffuse out of the steel and therefore accumulate at grain boundaries, creating voids, bubbles, and fissures. Over time, these defects:

• Weaken the metal

• Reduce toughness

• Cause micro-cracks and fissures

• Can eventually lead to major cracking or catastrophic failure

HTHA damage does not always cause wall thickness loss, making it difficult to detect using conventional inspection methods.

🔹 Why HTHA Inspection Is Critical

HTHA is considered a high-risk degradation mechanism because:

• Damage occurs internally

• Progression can be rapid and unpredictable

• Failure can be sudden and without warning

Early detection is essential to avoid unplanned shutdowns, equipment rupture, safety incidents, and plant losses.

🔹 Advantages of HTHA Inspection at TCR

• Inspection of large and wide areas

• Only external access required
  (No need for equipment opening or catalyst removal)

• Depth of hydrogen attack can be estimated

• Minimizes downtime and operational disruption

🔹 Limitations of HTHA Inspection

• High level of expertise required for data interpretation

• Very early-stage micro-level degradation (decarburization) may not be detectable by external methods alone

To overcome these limitations, TCR combines multiple inspection techniques for reliable assessment.

🔹 Technical Capabilities for HTHA Detection

HTHA inspection relies on advanced ultrasonic techniques that detect scattering and attenuation of ultrasound energy caused by internal fissures and voids.

Inspection Techniques Used by TCR

• Attenuation Measurement

• Velocity Measurement

• Spectral Analysis

• Scattered Signal Analysis

• High-Frequency Shear Wave UT for Welds & HAZ

• Advanced UT Methods:

  • Phased Array Ultrasonic Testing (PAUT)

  • Time of Flight Diffraction (TOFD)

All testing procedures are performed in line with API 941 guidelines.

🔹 Complementary Assessment Techniques

To improve accuracy and reliability, HTHA evaluation may also include:

• WFMPI (Wet Fluorescent Magnetic Particle Inspection)

• In-situ Metallography

• Hardness Testing

• Internal and External Inspection Combination

Testing from both sides, where feasible, helps overcome limitations of single-side inspection.

🔹 Applications

HTHA inspection services by TCR are applicable to:

• Pressure vessels

• Reactors

• Heat exchangers

• Hydrogen service piping

• High-temperature refinery and petrochemical equipment

🔹 Conclusion

At TCR Engineering & Services, High Temperature Hydrogen Attack (HTHA) inspection is performed using advanced ultrasonic techniques, industry standards, and expert interpretation to ensure early detection, risk reduction, and safe continued operation of critical assets.