Correction: Enhanced Hydrogen Embrittlement Resistance in a Vanadium-Alloyed 42CrNiMoV Steel for High-Strength Wind Turbine Bolts

In this paper, the frequent breakage of high-strength torsional shear bolts used in steel structure of a 2×350MW thermoelectric unit in northwest China is taken as an example. By means of macro and micro fracture analysis, physical and chemical inspection, the causes of frequent breakage of high-strength bolts are analyzed and the improvement measures are put forward. The results show that the failure of the 20MnTiB steel high-strength bolt after assembly is hydrogen embrittlement fracture, and the main cause of the failure is the presence of zinc layer on the bolt surface and a large number of zinc microholes on the shallow surface.

As the world increasingly gravitates towards green, environmentally friendly and low-carbon lifestyles, wind power has become one of the most technologically established renewable energy sources. However, with the continuous increase in their output power and height, wind turbine towers are subjected to higher-intensity alternating wind loads. This makes critical components more prone to fatigue failure, potentially leading to major accidents such as tower buckling or turbine collapse. High-strength bolts play a vital role in supporting towers but are susceptible to fatigue crack initiation under long-term cyclic loading, necessitating regular inspection. Types of wind turbine bolts mainly include high-strength bolts, stainless steel bolts, anchor bolts, titanium alloy bolts, and adjustable bolts. These bolts are distributed across different parts of the turbine and perform distinct functions. Among them, high-strength bolts in the tower are particularly critical for structural support, demanding prioritized periodic inspection. Compared to destructive offline inspection methods requiring bolt disassembly, non-destructive testing (NDT) has emerged as a trend in defect detection technologies. Therefore, this review comprehensively examines various types of NDT techniques for wind turbine towers’ high-strength bolts, including disassembly inspection techniques (magnetic particle inspection, penetration inspection, intelligent torque inspection, etc.) and non-disassembly inspection techniques (ultrasonic inspection, radiographic inspection, infrared thermographic inspection, etc.). For each technique, we analyze the fundamental principles, technical characteristics, and limitations, while emphasizing the interconnections between the methodologies. Finally, we discuss potential future research directions for bolt defect NDT technologies.

Evaluation method of sensitivity of hydrogen embrittlement for high strength bolts

Design and characterizations of novel Nb-ZrCo hydrogen permeation alloys for hydrogen separation applications

The hydrogen embrittlement of metals is caused by the penetration and accumulation of hydrogen atoms inside the metal. The failure of the product due to hydrogen embrittlement is delayed in time and does not occur immediately after its manufacture, but several hours, days, or even weeks later. Therefore, the chances of detecting hydrogen embrittlement when checking the quality of the finished product are very slim. The use of high-strength bolts in industry is associated with the risk of hydrogen embrittlement. This phenomenon poses a threat to the safe use of devices by limiting or completely losing the functionality of the bolt joint. Even a low influence of moisture can trigger failure mechanisms. The article proposes a method for assessing the risk of hydrogen embrittlement for high-strength bolts in class12.9. For this purpose, bolts made of material grade 32CrB4 were prepared and in a controlled manner the grain flow inconsistency was made, leading in extreme cases to the production of the forging lap. To perform the study, the device proposed by the European Assessment Document (EAD) was adapted to the testing of hydrogen embrittlement of threaded fasteners in concrete. The concrete substrate was replaced with metal spacers that were preloaded with a bolt. The use of the wedge distance under the bolt head led to the generation of two stress states – tensile and compressive, which translated into an increased risk of hydrogen embrittlement. After being tested, the bolts were visually and microscopically inspected to assess potential locations for cracks and hydrogen propagation. As a result of the conducted tests, it was found that the prepared test method allows to assess the resistance or susceptibility of the bolt to threats related to hydrogen embrittlement.

Synergistic enhancement mechanism of mechanical properties and hydrogen embrittlement resistance in medium Mn steels by coupling warm/cold rolling and delta ferrite

Influence of cold deformation and annealing on hydrogen embrittlement of cold hardening bainitic steel for high strength bolts

Effect of dislocation cell walls on hydrogen adsorption, hydrogen trapping and hydrogen embrittlement resistance

Wind energy as an inexhaustible green energy is the development trend of the future. Wind turbine bolts play an important role for the service safety of wind turbine, and have become the new promising product of the fastener industry in the world. But because of the high strength bolt connection failure caused by a tower pour accident, caused the attention of the scientific research workers, and put forward to improve reliability, high strength bolt connection to ensure that the wind turbine operation research problems. The rigid strength, toughness and hardenability requirements of the wind turbine bolt steels are really challenging work. Based on the fatigue life model,the calculation method of the fatigue reliability index of high strength bolt in the grid structure with bolt-sphere joints is discussed and some important parameters are gained.

Susceptibility to hydrogen embrittlement (HE) is an ongoing concern for high-strength structural bolts. We evaluated the HE susceptibility of three high-strength alloys including a martensitic stainless steel, a high-strength carbon steel, and a duplex stainless steel. We conducted HE testing according to the Incremental Step Loading Technique of ASTM F1624. In order to charge the specimens with hydrogen, we used an electrochemical charging method and compared charging the specimens prior to testing to in situ charging during testing. We determined that in situ charging results in improved penetration of hydrogen into the test specimen compared to precharging, and thus provides a more accurate evaluation of the HE susceptibility of structural bolts.

A high-strength bolt of a steel structure of a nuclear power plant failed and fell off. In order to determine the cause of the bolt’s fracture, a series of tests such as macro inspection, physical and chemical performance test, and microscopic analysis of the fracture were carried out on the failed bolt. The results show that the cause of bolt fracture is hydrogen embrittlement. Hydrogen infiltrated into the bolt during the phosphating process and the corrosion process during use, and then hydrogen continued to accumulate eventually causing hydrogen embrittlement fracture. Dehydrogenation treatment should be performed immediately after the phosphorylation treatment, and the anti-corrosion method of the bolt should be optimized, which is an effective measure to prevent the hydrogen embrittlement of high strength bolts.

Earlier studies have shown that interlath austenite in martensitic steels can enhance hydrogen embrittlement (HE) resistance. However, the improvements were limited due to microcrack nucleation and growth. A novel microstructural design approach is investigated, based on enhancing austenite stability to reduce crack nucleation and growth. Our findings from mechanical tests, X-ray diffraction, and scanning electron microscopy reveal that this strategy is successful. However, the improvements are limited due to intrinsic microstructural heterogeneity effects.

In the wind turbine system, high strength bolt is always used in important joint. For example, whether the bolt between wind turbine tower is safe is one important side of wind turbine protecting. However, the gearbox always loses oil even if wind turbine runs well, even the oil would leak on the bolt joint of each layer. So it is important to analysis the influence of oil-leak to bolt joint. Through analyzing the property of gear oil and the stress situation of bolt in wind turbine tower, the paper obtains the equilibrium formula of bolt joint in different stress situation and the influence of oil to frictionfactor and torque coefficient. At last, making a conclusion about the reson of causing bolt joint loosing when gearbox oil leaks on the bolt joint of wind turbine tower.

Looseness of high-strength wind turbine bolts is one of the main types of mechanical failure that threaten the quality and safety of wind turbines, and how to non-destructively detect bolt loosening is essential to accurate assessment of operational reliability of wind turbine structures. Therefore, to address the issue of looseness detection of high-strength wind turbine bolts, this paper proposes a non-destructive detection method based on digital image correlation (DIC). Firstly, the mathematical relationships between the inplane displacement component of the bolt’s nut surface, the bolt’s preload force loss and the bolt loosening angle are both deduced theoretically. Then, experimental measurements are respectively conducted with DIC with different small bolt loosening angles. The results show that the bolt loosening angle detection method based on DIC has a detection accuracy of over 95%, and the bolt’s preload force loss evaluated by the deduced relationship has a good agreement with the empirical value. Therefore, the proposed DIC-based bolt loosening angle detection method can meet the requirements of engineering inspection, and can achieve quantitative assessment of preload forces loss of wind turbine bolt.

Fragilização por hidrogénio no aço ABNT 10B22 modificado carbonitretado temperado e revenido a 400 °C