Criteria of Material Failure in Relation to Hydrogen Saturation

A steadily rising interest which specialists in various fields show towards the problem of hydrogen affecting metallic materials and causing their failure is connected to all-increasing requirements set on the durability of machines and equipment in operation. Metallic structures are most often surrounded by such environment which contains hydrogenous components or hydrogen itself (in chemical industry, power engineering, etc). And it leads to various types of degradation in metals (hydrogen embrittlement, hydrogen corrosion, and so on), which, in its turn, could cause catastrophic results. Ultimate strength is considered to be a representative parameter of the process of hydrogen degradation in steels. The authors cite the results of testing conducted on hydrogen-saturated specimens made of A516-55 steel which register a significant decrease in the ultimate strength. It is proposed to use a diagram which describes a fall in metal strength and transition of structural materials into their brittle states following an increase in hydrogen concentration. Discussion is made on criteria for hydrogen-saturated materials of metallic structures failing when a momentary overload occurs under default working conditions.

Correlation between Microstructure and Hydrogen Degradation of 690 MPa Grade Marine Engineering Steel

Electrochemical H charging, hydrogen permeation, and hydrogen-induced cracking (HIC) behavior of 690 MPa grade steel substrate and different heat-treatment states (annealed, quenched, normalized, tempered) are investigated by cyclic voltammetry (CV), hydrogen permeation, electrochemical H charging, and slow strain rate tensile test (SSRT). The results show that hydrogen diffuses through the steel with the highest rate in base metal and the lowest rate in annealed steel. The hydrogen-induced cracks in base metal show obvious step shape with tiny cracks near the main crack. The cracks of annealed steel are mainly distributed along pearlite. The crack propagation of quenched steel is mainly transgranular, while the hydrogen-induced crack propagation of tempered steel is along the prior austenite grain boundary. HIC sensitivity of base metal is the lowest due to its fine homogeneous grain structure, small hydrogen diffusion coefficient, and small hydrogen diffusion rate. There are many hydrogen traps in annealed steel, such as the two-phase interface which provides accommodation sites for H atoms and increases the HIC susceptibility.

A critical appraisal of laser peening and its impact on hydrogen embrittlement of titanium alloys

Many efforts have been made to understand the effects of hydrogen on titanium alloys, resulting in an abundance of theoretical models and papers. Titanium alloys are crucial advanced materials that provide an excellent combination of a high strength-to-weight ratio and good corrosion behaviour even though they are reasonable to corrosion attack. Titanium alloys are susceptible to hydrogen embrittlement when comes into contact with hydrogen, and galvanic pair with an active metal current, or the pH is greater than 12 or less than 3 or an impressed current. In view of the fact that hydrogen behaves differently with α and β phases, hydrogen degradation may vary markedly in titanium alloys. Hydrogen diminishes the corrosion and erosion resistance and fatigue life of in-service titanium components. A laser peening or laser shock peening is a novel technique for making the metal surfaces and sub-layers densify. It evokes that laser shock peening adoption results in yielding and plastic deformation, thereby creating high compressive residual stresses extending below the surface of the material which is desirable for hydrogen embrittlement resistance and reduction of crack initiation and growth of the component. This article is a review of information relating hydrogen embrittlement of titanium alloys and surface modification technique which influence the strength potential of titanium alloys.

Comparison of resistance to damage of unalloyed carbon steels under the influence of hydrogen

One of the most commonly used construction material in industry is unalloyed steel S235 and S355. These types of steel are used for construction of ships, bridges, coastal construction, welded tanks, and in buildings. Due to the operating conditions, these types of steel may undergo hydrogen degradation in the process of manufacturing of welded structures or when operating the structures. This paper presents the results of study into resistance of selected types of non-alloy structural steels to hydrogen degradation. Tests were carried out to determine changes in mechanical properties in the static trials of stretching without hydrogen, and after saturation with hydrogen. Parallel fractographic and electrochemical studies were carried out. Hydrogen saturation was carried out at the time from 3. up to 24. hours in a solution of 0.1N H2SO4 with the addition of 2 mg/dm3 arsenic oxide (III) at an electric current density of 20 mA/cm2. The results of the tests have shown that the impact of hydrogen on the tested steels S235JR and S355J2 leads to a significant deterioration in their mechanical and electrochemical properties. At comparable concentrations of hydrogen, steel S235JR is less susceptible to hydrogen degradation and has greater corrosive resistance measured in 3% NaCl solution, in comparison with steel S355J2.

Hydrogen Influence on Microstructure and Properties of Novel Explosive Welded Corrosion Resistant Clad Materials

The aim of this work was to investigate whether the explosively welded metals are susceptible to hydrogen degradation. The materials described in this article are widely used nickel alloy Inconel C-276 and super duplex steel SAF 2507 as clad materials for their superior resistance to corrosive environment and low alloy steel P355NH as a base material. It was observed that at the explosive bonded interface between the base steel and the stainless steel some local melting zones are formed. It was found that the cathodic hydrogen charging causes changes in the microstructure of bonded materials and decreases the shear strength of bonds as well as the corrosion resistance of clads.

Hydrogen Influence on Microstructure, Corrosion Resistance and Mechanical Properties of Low Alloy Steel and Explosively Cladded Steel Used for Hydrogen Storage Salt Caverns

The aim of this work was to investigate whether the low alloy steel and the explosively welded metals used for salt caverns equipment's are susceptible to hydrogen degradation. The materials described in this article are cheap and widely used 09G2S low alloy steel and titanium grade1 as a clad material for its superior resistance to corrosive environment joined explosively with low alloy steel S355J2+N. It was observed that at the explosive bonded interface between the base steel and the stainless steel some local melting zones are formed. It was found that the cathodic hydrogen charging causes changes in the microstructure of low alloy steel and decreases the shear strength of bonds and tensile stress as well as the corrosion resistance of clads.