Causes of cracks in boiler and pressure vessels and corresponding measures

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Causes of cracks: 1. Stress corrosion cracks. During the operation of a boiler, when the boiler’s steel plates are exposed to alkali water at high concentrations, a potential difference is generated between the metal crystals. The high potential of the grains themselves forms the cathode, while the low potential between the grain boundaries forms the anode; this causes corrosion to progress deeper along the grain boundaries, leading to the formation of cracks. If the cracks are caused by caustic embrittlement, they will propagate from the inside outward, and the cracks will mainly concentrate in areas under high stress. 2. Fatigue cracks: Fatigue cracks can be further divided into mechanical fatigue and corrosion fatigue; the formation of such cracks is a common phenomenon during the regular inspections of boilers. The part related to corrosion fatigue arises from the interaction of alternating stress and corrosive agents, on the basis of the formation of fatigue cracks. The macroscopic characteristics of mechanical fatigue cracks are mainly linear in shape; at the initial stage the cracks are short, expanding inward in a tunnel-like manner, and as the fatigue level increases, the crack propagation accelerates, with two-way cracking occurring in severe cases ； In terms of microscopic characteristics, the main influences come from the stress conditions and the environmental medium, making the situation complex. The formation of corrosion fatigue cracks is similar to that of fatigue cracks, with a slow rate of progression, making them difficult to detect during actual inspections. 3. Overheating and overburning cracks: This type of boiler crack occurs primarily in the manufacturing and forging industries, and it involves both macroscopic and microscopic characteristics. At the macroscopic level, the cracked surface caused by over-sintering features numerous cracks of varying sizes; traces of melting or severe oxidation at the grain boundaries could be observed, along with a large number of cracks and fragments on the surface ； At the microscopic level, the microstructures of overheating or overburning are both related and distinct; their common feature is coarse grains. The essence of overburning lies in the fact that, due to the relatively high heating humidity, oxidizing gases diffuse outward from the grain boundaries, causing molten compounds to appear on the surface of the grains; under microscopic observation, voids as well as an oxidized grain boundary network can be easily identified. Measures to prevent cracks: 1. Operational control. Boilers are widely used in industrial production as well as in daily social activities, where they facilitate the conversion of energy. The crack problem in boiler pressure vessels is closely related to the level of human operation. To prevent the formation of cracks, it is crucial to control the operating procedures of the staff. However, at present, the personnel responsible for boiler operation have not received training on professional skills, which results in their limited familiarity with the operating procedures; as a consequence, operational errors occur, severely affecting the safety of the boilers. Therefore, in this regard, it is necessary to strengthen the training of boiler operators, clarify specific operating procedures, conduct necessary assessments, and pay greater attention to these procedures in order to fundamentally prevent crack formation caused by improper human operation. 2. Raw material control: The occurrence of crack problems in boiler and pressure vessels is closely related to the production quality of the raw materials. Therefore, before starting the production of boiler vessels, it is necessary to carefully examine the drawings to clarify the specific requirements, ensuring that the vessel production is carried out in accordance with relevant standards and that all processing steps and production phases are effectively controlled. Furthermore, the production of boiler pressure vessels requires clear production management regulations to ensure that operations take place within the framework of procedural documents and quality control measures, thus guaranteeing the proper progress of the manufacturing process. 3. Quality control: As high-risk equipment, boilers require strict quality control during production to ensure that errors remain within acceptable limits. Therefore, strict self-inspection as well as mutual inspection are essential; by strictly controlling the production processes, it is possible to improve the quality of boilers and minimize the occurrence of cracks.