High Temperature Hydrogen Attack (HTHA)

High Temperature Hydrogen Attack (HTHA): Detection, Assessment, Evaluation

High temperature hydrogen attack (HTHA) is a phenomenon which occurs within some industrial processes when the presence of hydrogen, subjected to high temperature and pressure, makes plants and systems susceptible to damage. This reaction can cause an industrial plant to suffer serious failure, which may lead to both expensive repairs and loss of production.

HTHA can be detected in a number of ways, but it is considered that with the complexity of HHTA a more structured approach is necessary. A series of procedures have been developed featuring the latest advances in ultrasonic imaging and data processing techniques in order to achieve a greater level of confidence in both HTHA inspection results and inspection repeatability.

With a full understanding of both the phenomena and the methods to assess it, we feel our HTHA service will help minimize your risk. Our experienced technicians are able to efficiently evaluate the presence of hydrogen damage and so prevent failure of critical plant equipment. The information recorded can be later on analyzed allowing fitness for service calculations.

TÜV Rheinland Sonovation is part of the TÜV Rheinland Group specialized in providing a complete range of advanced non-destructive testing (NDT) services. In addition to operating a competence center for advanced NDT based in the Netherlands, it maintains branches in the United Kingdom, Belgium, Germany and Saudi Arabia. Acknowledged as leaders in the field, TÜV Rheinland Sonovation invests heavily in R&D and operates an accredited training school for advanced NDT as well as offering its expert services globally.

Benefits of Our High Temperature Hydrogen Attack Services at a Glance

Using our HTHA services you get:

  • Latest digital techniques available for the detection of high temperature hydrogen attack.
  • High reliability and reproducibility.
  • Up to date data processing techniques.
  • Clear presentation of results.
  • Examinations of numerous different geometries such as vessels and piping.
  • Accurate monitoring of damage progress by means of repeated inspections.
  • A lead against the competition using our neutral audit seal.
  • TÜV Rheinland´s exclusive one-stop-shop services.

Available HTHA Inspection Techniques in Accordance with the American Petroleum Institute (API) 1941 Guideline

Backscatter
The backscatter technique is used to detect suspicious areas affected by hydrogen attack. The front of the attack in the material can be measured and imaged. The remaining wall thickness (un-attacked) is assigned a color. Using this technique the operator is able to create backscatter patterns and evaluate directional and frequency dependence.

Velocity ratio measurement
Velocity ratio measurement, on the other hand, is used as a cross-check to confirm the findings of the backscatter measurement. It is based on the principle that the longitudinal and transverse sound velocities are affected by HTHA. This way the percentage of attack can be measured and even a differentiation between small inclusions and HTHA is possible.

Time of flight diffraction (Tofd)
With time of flight diffraction (Tofd) testing it is possible to inspect structures for defects caused by HTHA. It can be used for the detection of both macro and micro cracks

Areas for Application of HTHA

Backscatter and velocity ratio measurement are used for the inspection of the parent material. Time of flight diffraction is used for the inspection of the weld material.

Inspection Strategy

  • High susceptibility paired with operating conditions at or above Nelson Curves: high inspection coverage: backscatter mapping, velocity ratio measurement, Tofd, 45° shear wave inspection
  • Medium susceptibility paired with operating conditions up to 25°F below Nelson Curve: medium inspection coverage, backscatter mapping, manual testing, velocity ratio measurement, ToFD, 45°
  • Low susceptibility paired with operating conditions 50°F below Nelson Curve: low inspection coverage: manual backscatter, ToFD

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