High Temperature Hydrogen Attack: New NDE Advanced Capabilities — Development and Feedback

In petroleum industry, hydrogen is used in many assets. With temperature and pressure, hydrogen can damage materials. This damage is called High Temperature Hydrogen Attack (HTHA) and is a time dependent degradation mechanism that can affect the integrity of steels used for pressure containment operating above about 400°F (204°C). HTHA has caused major accidents in Petroleum Industry. API RP 941 [1] currently provides guidance for steel selection (and so susceptibility to attack) in relation to temperature and ppH2 via Nelson curves. In the last edition, 4 stages of degradation for both base metal and weld metal are described. In the past, only stage III was detectable by the combination of different Ultrasonic methods which were known as AUBT – Advanced Ultrasonic Backscatter Technique. But, capability of detection was limited to defects above 500–1000μm, correspondent to small fissures. So, it was impossible to detect early stage of degradation as steel grain size (around 50μm). For several years, performances of non-destructive techniques have rapidly increased and new advanced ultrasonic technologies are available such as: - Phased Array Ultrasonic Techniques (PAUT) - Time Of Flight Diffraction (TOFD) - Total Focusing Method (TFM) This paper describes latest techniques and results obtained by Total and French Welding Institute in laboratory, and discuss the efficiency of the methods, over real HTHA degradation blocks. An overview of TFM is also proposed by CEA who work on innovating development to increase the performance of this technique.