NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

Industrial plants where Hydrogen occurs at high temperatures and pressures may be susceptible to Hydrogen damage. Hot Hydrogen Attack (HHA) is the formation of methane (CH₄)by reaction with carbides in the steel. HHA can occur in several types of alloys in both the parent and weld material. The probability of HHA depends on the partial hydrogen pressure and the operating temperature. The methane formed accumulates at internal voids on the grain boundaries, where at sufficient pressure, the build-up can produce microcracks. In the weld material there is normally leakage before rupture but in the parent material, rupture can be sudden.

The development of a novel inspection approach within AEA Sonomatic BV in the Netherlands using the various inspection software utilities in the Microplus ( µ⁺ ) System ensures early detection of this phenomenon with high reliability and reproducibility.The detection of HHA in the parent metal is possible combining the following two ultrasonic techniques.

1. Backscatter measurement.
2. Velocity ratio measurement.

The backscatter technique is based on the detection of ultrasonic backscatter received from the microcracks. The advantage of this is that 100% coverage of the surface is possible. Velocity ratio measurements are used to observe the changes in the velocity ratios between the longitudinal and transverse waves. With an advanced calculation program, it is possible to calculate the stage of attack. This is a very reliable result so long as the attacked wall thickness is over 10% of the total wallthickness.

HHA in the weld material is detected using the Ultrasonic Time-Of-Flight Diffraction (TOFD) technique. Both micro and macro cracks are detectable. Monitoring using the above approach is simple and effective as baseline data is stored.
This paper will also discuss the field-results obtained using this approach and highlight the practical advantages in such cases.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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