Crack Initiation and Propagation Under Hydrogen-Enhanced Fatigue of a Cr-Mo Steel for Gaseous Hydrogen Storage

2014 ◽  
Author(s):  
Laurent Briottet ◽  
Marielle Escot ◽  
Isabelle Moro ◽  
Gian Marco Tamponi ◽  
Jader Furtado ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Hydrogen Storage ◽  
Crack Growth ◽  
Hydrogen Pressure ◽  
Pressure Vessels ◽  
Gaseous Hydrogen ◽  
Crack Initiation And Propagation ◽  
High Hydrogen ◽  
Initiation And Propagation

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of such vessel used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. Yet, hydrogen can reduce the fatigue life in two ways: by decreasing the crack initiation period and by increasing the fatigue crack growth rate. The European project MATHRYCE aims are to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue. The study is focused on a low alloy Cr-Mo steel, exhibiting a tempered bainitic and martensitic microstructure, and classically used to store hydrogen gas up to 45 MPa. Due to hydrogen diffusion at room temperature in such steel, tests have to be performed under hydrogen pressure to avoid outgassing. In the present work, experimental procedures have been developed to study both crack initiation and crack growth. The specimens and tests instrumentation have been specifically designed to quantitatively measure in-situ these two stages under high hydrogen pressure. We developed and tested crack gages located close to a small drilled notch. This notch simulates the presence of steel nonmetallic inclusions and other microstructural features that can affect fatigue crack initiation and propagation. The experimental results addressing the effects of the testing conditions, such as stress ratio, frequency and hydrogen pressure will be compared to the local strain and stress fields obtained by Finite Element Method and correlated to the possible hydrogen enhanced fatigue mechanisms involved.

Hydrogen-Enhanced Fatigue of a Cr-Mo Steel Pressure Vessel

2015 ◽  
Author(s):  
L. Briottet ◽  
I. Moro ◽  
J. Furtado ◽  
J. Solin ◽  
P. Bortot ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Pressure Vessel ◽  
Hydrogen Pressure ◽  
Fatigue Crack Initiation ◽  
Pressure Vessels ◽  
Full Scale ◽  
International Standards ◽  
High Hydrogen ◽  
Initiation And Propagation

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of vessels used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. In this context, the European project MATHRYCE intends to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue. In the present document the lab-scale experimental developments and results are presented. The material considered was a commercially available Q&T low alloy Cr-Mo steel from a seamless pressure vessel. Due to the high hydrogen diffusion at room temperature in such steel, all the tests were performed under hydrogen pressure to avoid outgassing. Different types of lab-scale tests were developed and used in order to identify the most promising one for a design code. The effect of mechanical parameters, such as H2 pressure, frequency and ΔK, on fatigue crack initiation and propagation was analyzed. In particular, special attention was paid on the influence of H2 on the relative parts of initiation and propagation in the fatigue life of a component. The second part of the work was dedicated to cyclic hydraulic and hydrogen pressure tests on full scale vessels. Three artificial defects with different geometries per cylinder were machined in the inner wall of each tested cylinder. They were specifically designed in order to detect fatigue crack initiation and fatigue crack propagation with a single test. The final goal of this work is to propose a methodology to derive a “hydrogen safety factor” from lab-scale tests. The proposed method is compared to the full-scale results obtained, leading to recommendations on the design of pressure components operating under cyclic hydrogen pressure.

Fatigue Crack Initiation and Propagation in Cr-Mo Steel Hydrogen Storage Vessels: Research on Design for Safe Life

2016 ◽  
Author(s):  
Jussi Solin ◽  
Laurent Briottet ◽  
Beatriz Acosta ◽  
Paolo Bortot ◽  
Jader Furtado ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Design Procedure ◽  
Pressure Vessels ◽  
International Standards ◽  
Crack Initiation And Propagation ◽  
Joint Research ◽  
Initiation And Propagation

International standards and codes dedicated to design of pressure vessels are still unable to competitively ensure safe design and fitness for service of steel vessels for high pressure gaseous hydrogen. Emptying and shallow pressure cycles subject the material to hydrogen enhanced fatigue. A pre-normative project, MATHRYCE under the EU joint research program focused in this subject through material and component testing, analytical work, review of design methodologies and international collaboration. An easy to implement, safe and economically competitive vessel design methodology is targeted. Steps towards this goal were taken by deepening our understanding on hydrogen enhanced fatigue in different kinds of laboratory specimens and real vessels designed for hydrogen service at maximum 45 MPa pressure. This included cyclic pressure testing of artificially notched vessels both in hydrogen and inert environment. The effect of hydrogen pressure, frequency and mechanical loading parameters (ΔK, Sa) on fatigue crack initiation and propagation was analyzed. Attention was paid on the definition of “initiation” and influence of hydrogen on the relative parts of initiation and propagation on the fatigue life of a component. A good correlation between results with various test types was found. Particularly promising was the match between the measured — and estimated — crack growth rates in laboratory specimens and vessels. This supports our proposal for a safe design procedure based on crack growth and defect tolerant approach. Recommendations for implementation in a new international standard, on how to properly address hydrogen enhanced fatigue based on laboratory tests, were given and will be summarized in this presentation. Our results indicate that crack initiation from inclusions or other small microstructural features is not necessarily affected by hydrogen to a similar extent as crack growth, but when initiated, the remaining life may be short due to fast growth. This is challenging for design and inspection rules to allow economically competitive construction of hydrogen equipment without compromising safety.

Fatigue Crack Growth Behavior of Threaded Pipe Couplings

2011 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Patrick De Baets ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Fracture Surface ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Crack Opening ◽  
Bending Test ◽  
Crack Initiation And Propagation ◽  
Accurate Knowledge ◽  
Initiation And Propagation

Threaded couplings are used in various applications to connect steel pipes. To maintain a secure connection, such couplings are preloaded and during service additional dynamic loads can act on the connections. The coupling’s threads act as stress raisers, initiating fatigue cracks, which can cause the connection to fail in time. Accurate knowledge of the fatigue behavior, taking into account crack initiation and propagation is necessary to understand the fatigue mechanisms involved. In this study, the fatigue behavior of tapered couplings with NPT threads is studied. This is done by analyzing the results of an experimental four-point bending test. The fatigue crack propagation is monitored using an optical dynamic 3D displacement measurement device and LVDTs to measure the crack opening. At certain times during the test, the load ratio is changed to apply a number of beach marking cycles. This way a fine line is marked in the fracture surface. These marked crack shapes are used as input for a finite element model. The measured deflection and crack opening are compared to the results of the numerical simulations. Using this methodology a distinction is made between fatigue crack initiation and propagation. By analyzing the fracture surface it was observed that once the crack is initiated, it propagates over a wide segment of the pipe’s circumference and subsequently rapidly penetrates the wall of the pipe. The observed crack growth rates are confirmed by a fracture mechanics analysis. Since the appearing long shallow crack is difficult to detect at an early stage the importance is demonstrated of accurate knowledge of the fatigue behavior of threaded connections in order to define acceptable flaw sizes and inspection intervals.

Fatigue crack paths and properties in A356-T6 aluminum alloy microstructurally modified by friction stir processing under different conditions

2015 ◽  
Author(s):  
A. Tajiri ◽  
Y. Uematsu ◽  
T. Kakiuchi ◽  
Y. Suzuki
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Friction Stir Processing ◽  
Casting Defects ◽  
Processing Conditions ◽  
Tool Rotational Speed ◽  
Crack Initiation And Propagation ◽  
Friction Stir ◽  
Initiation And Propagation

A356-T6 cast aluminum alloy is a light weight structural material, but fatigue crack initiates and propagates from a casting defect leading to final fracture. Thus it is important to eliminate casting defects. In this study, friction stir processing (FSP) was applied to A356-T6, in which rotating tool with probe and shoulder was plunged into the material and travels along the longitudinal direction to induce severe plastic deformation, resulting in the modification of microstructure. Two different processing conditions with low and high tool rotational speeds were tried and subsequently fully reversed fatigue tests were performed to investigate the effect of processing conditions on the crack initiation and propagation behavior. The fatigue strengths were successfully improved by both conditions due to the elimination of casting defects. But the lower tool rotational speed could further improve fatigue strength than the higher speed. EBSD analyses revealed that the higher tool rotational speed resulted in the severer texture having detrimental effects on fatigue crack initiation and propagation resistances.

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