FCTM Esope


Oct 7, 2021 | 3:00 PM - 3:30 PM

Le Montage


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 400ºF (204ºC). HTHA caused major accidents in Petroleum Industry. API RP 9411 currently provides guidance for steel selection (and so susceptibility to attack) in relation to temperature and ppH2 via Nelson curves. It also describe 4 stages of degradation for both base metal and weld metal. In the past, only stage III was detectable by the combination of different Ultrasonic method which were known as AUBT – Advanced Ultrasonic Backscatter Technique. But, capability of detection was limited to defects above 500 – 1000μm, as size of 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 has increased rapidly and new advanced ultrasonic technologies are available such as: - Phased Arrays 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 on sites, and discuss the efficiency of the methods, over real HTHA degradation blocks. The best effectiveness to detect HTHA by UT methods is achieved: - By using multiple UT techniques, (TOFD, PAUT beam forming and TFM/FMC), which aim at imaging small defects with optimal resolution, with versatile application thanks to phased array probes. - With skilled technicians having a good understanding of the HTHA damage and its ultrasonic responses, - With a good surface preparation to allow high frequency probes for increased spatial resolution - With specific HTHA reference blocks to set up the UT instruments thanks to metallurgical expertise To assure the identification of the indications detected by ultrasonic examination, field metallographic examination methods (replicas and boat samples) are the most relevant, since detailed expertise can be carried out in laboratory. It is then possible to identify the ability of advanced NDE methods to detect HTHA degradations at the early stages. Total and his partners French Welding Institute and CEA continue to invest in mastering of the best non-destructive examination techniques through a survey of advanced NDE techniques and their potential applications to the oil and gas industry, as well as experimental tests, to detect and identify HTHA degradations at early stage and to guarantee the integrity of its industrial assets.

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