#1 High temperature hydrogen attack new NDE advanced capabilities development and feed back
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.
#2 Fitness-For-Service Techniques for High Temperature Hydrogen Attack Damage
High-temperature hydrogen attack (HTHA) is a damage mechanism that can adversely affect the service life of carbon steel and low-chrome steel pressure equipment in the petroleum refining, ammonia production, and related industries. Long-term exposure to high-temperature hydrogen environments can lead to volumetric HTHA damage, due to the formation and coalescence of material micro voids, that can diminish the load carrying capacity of pressure equipment and can accelerate the propagation of crack-like flaws, especially near welds. This paper summarizes some evolving developments in HTHA technology and discusses methods for modeling HTHA damage progression. Additionally, recent enhancements in non-destructive examination (NDE) are explored. Furthermore, an outline of how these new engineering and inspection technologies will impact industry Codes and Standards and recommended practices is provided. An overview of fitness-for-service (FFS) techniques to provide protection against plastic collapse, crack growth, and brittle fracture due to HTHA damage are presented. Furthermore, based on advanced engineering analysis and inspection, integrity operating windows (IOWs) can be established to maintain safe operating limits for affected equipment. Lastly, this paper offers insight into identifying HTHA risks, predicting damage progression over time, and employing risk mitigation strategies.