HTHA – High-Temperature Hydrogen Attack

When steel and steel alloys are exposed to high temperatures, a high-temperature hydrogen attack (HTHA) occurs.

HTHA is a common problem in refineries, manufacturing plants, and petrochemical plants. HTHA causes a number of defects in steel assets, including decarburization, reduced strength, and even asset failure. Extensive research has been conducted to investigate a reliable method of evaluating equipment that has a high risk of HTHA damage.

To further evaluate and characterize suspect damage, Advanced NDT Solutions has adopted a multi-ultrasonic technique approach that includes industry-accepted techniques as well as supplemental Phased Array & TOFD technology.

High Temperature Hydrogen Attack Inspection in UAE - Aqualis

Technique #1 – Ultrasonic Backscattering: This technique is based on the idea that changes in grain boundaries caused by hydrogen damage will scatter ultrasound. The extent of this damage is directly proportional to the through-wall depth value of the affected material thickness and its location in relation to the ID/OD surfaces. Using a 10 Mhz and a 5 MHz transducer combination.

Technique #2 – Velocity Ratio Calculations: Greater than 20% HTHA damage will change the relationship between the ultrasonic velocities of longitudinal and shear-wave transit times. Normal undamaged material should have a ratio between 0.54 and 0.55. Velocity L / Velocity S = Formula Ratio.

Technique #3 – Spectral Analysis (FFT): The first back-wall signal is converted from a time domain to a signal attenuation (dB) with respect to a frequency domain for ultrasonic spectrum analysis. A clean location will not exhibit an increase in ultrasonic attenuation as frequency is increased, whereas an HTHA damaged region will.

Technique #4 – High-Frequency Shearwave of Welds & HAZ According to recent research, using a high-frequency shear-wave examination of welds and the HAZ can also aid in the detection of HTHA damage. This method employs a pitch-catch ultrasonic technique with two 10MHz 45° shear-wave probes.

HTHA Inspection Services in UAE - Aqualis Inspection Services

Technique #5 – Phased Array Ultrasonic Testing using TFM/FMC: The total focusing method algorithm, which is approved by API 941, is an advanced and new technology, and it can provide greater clarity and precision than standard phased array ultrasonic testing.