The durability of materials exposed to corrosive conditions is a major stake as it affects process and plant safety and implies large costs. In real applications and in future “zero emission technologies”, metallic alloys are and will be subjected to oxidizing and water-rich environments at high temperature. Under such conditions, the volatilization of the chromia scale takes place, speeding up the material end of life. While the chromium loss due to volatilization has been estimated many times to assess the material lifetime in past and recent studies, the gas phase evolution and its influence on the volatilization rate are rarely considered although they affect the alloy end of life. To respond to such problem, the DYNAMIC project, which associate 3 academic labs with 2 industries, proposes to evaluate the high temperature oxidation of refractory metallic alloys and the volatilization of their protective oxide layer by an original approach combining high temperature oxidation tests and simulations of the gas phase. Oxidation tests will be carried out between 600 and 1100 °C, under intermediate to high gas velocities (from few tens of cm.s-1 to few m.s-1) and over the complete water vapour content range, i.e. from few ppm to nearly 100 %. Also, characterizations of the samples, before and after oxidation, will be performed. In parallel, the gas phase within the oxidation rigs and the volatilization reaction will be simulated by computational fluid dynamics (CFD). This methodology will be conducted to better understand the influence of dynamic flows on oxidation and volatilization kinetics, and therefore the degradation mechanisms at work in such environments. It shall make it possible the determination of laws capable of predicting lifetime and the evaluation of the effects of geometry to propose solutions to delay the end of life of alloys.

The development of hydrogen as a reliable energy vector is strongly connected to the performance and level of safety of the components of the supply chain. In this respect, achieving an efficient storage is crucial to address transition markets and automotive markets. For near term, compressed hydrogen storage is currently the most promising technology. Compressed hydrogen for industrial applications is stored at 200 bar in metallic cylinders which have poor mass storage efficiency but present high impact resistance. To achieve required performance in terms of autonomy and weight efficiency, hydrogen must be stored at pressure up to 700 bar in carbon fibers composites cylinders. However the damage resulting from a shock, its evolution during service and thus the cylinder tolerance to damage are not well described. As a consequence, the design of the composites cylinders is conservative and even minor shock on cylinder results in the cylinder withdrawal from the supply chain, which affects the cost without an enhanced guaranty of safety. In the scope of hydrogen energy markets, the cylinders can be subjected to a broad range of impacts either usual or accidental (car accident, during handling and transportation of transportable cylinders) and can be in the hand of people with no experience of compressed gas handling. It is thus critical to assess impact resistance of the storage and to determine which impact causes a cylinder burst immediately or after some time in service. In addition, taking into account that some 2015 DOE performance targets are almost reached by composites cylinders and that there are on-going projects to improve manufacturing & materials, a study on damage tolerance of these structures (i.e. thick composites made by filament winding) is justified and would be complementary to current approach. The development of scientific knowledge on the behavior of carbon fiber composites cylinder subjected to impacts and of numeric tools to predict residual performance of a cylinder in service presenting damage from a shock are the main objective of the project TOLEDO, submitted to the French call “AAP ANR HPAC 2010. The project gathers an industrial partner Air Liquide as an end-user of composites cylinders with experience on cylinder supply chain and safety, CEA who has cylinder testing facilities and cylinder design experience and two academic partners with complementary competences in impact generation, damage characterization and composites structure durability that are acknowledged by the academic world (LAMEFIP from ENSAM Bordeaux and Institut P’ – ENSMA, Poitiers). In the framework of TOLEDO program, a significant number of high pressure composites cylinders will thus be subjected to drop and shock tests representative of normal and accidental situations in the Hydrogen Energy supply chain and during handling by the customer. Different techniques will be used to characterize the resulting damage on the composite structure. The criticality of the damage for the cylinder will be assessed by the study of residual performance of the cylinder after the impact and more importantly after further use (static and cyclic pressure load, effect of temperature). This part of the study will involve tests on specimens, a numeric study and a validation on cylinders and will provide knowledge on lifetime predictions. This approach will lead to recommendations for the industry and normative committees on the design of cylinders taking into account a quantitative analysis of damage tolerance and possible protections and for the control of cylinders in service by providing knowledge to define a withdrawal threshold.