Equipment in the petrochemical industry often needs to withstand a variety of complex stresses, such as alternating stress, high temperature and high pressure, which can lead to fatigue damage of materials, thus affecting the safety and service life of equipment. As an important part of equipment, the fatigue performance and life prediction of petrochemical forgings are of great significance to the safety and service life of the whole equipment. In this paper, the fatigue properties and life prediction methods of petrochemical forgings are discussed in order to provide reference for related research and application.
Fatigue properties of petrochemical forgings
Fatigue crack initiation: Under the action of alternating stress in petrochemical forgings, cracks often start from defects on the surface of the material. The rate and number of initiation cracks depend on the nature of the material, stress level, environment and other factors.
Crack propagation: Once a crack is initiated, it will gradually expand under the action of alternating stress. The rate of crack propagation depends on the stress intensity factor of the crack tip and the fracture toughness of the material.
Transient fracture: When the crack extends to a certain extent, the forging will not be able to withstand the alternating stress and transient fracture occurs. Transient fracture is the last stage of fatigue failure, which is sudden and catastrophic.
Factors affecting fatigue properties of petrochemical forgings
Material properties: The strength, toughness, hardness and other properties of the material will affect its fatigue performance. In general, the fatigue limit of high-strength materials is also relatively high.
Stress level: The amplitude and frequency of alternating stress will affect the fatigue performance of forgings. High stress levels and frequencies lead to faster fatigue damage.
Temperature and environment: High temperature and high humidity will accelerate the fatigue damage of the material. In addition, corrosive media can also adversely affect the fatigue properties of materials.
Forging and heat treatment processes: Forging and heat treatment processes affect the microstructure and mechanical properties of the material, thus affecting its fatigue properties.
Life prediction method of petrochemical forgings
Nominal stress method: According to the S-N curve of the material and Miner’s linear cumulative damage theory, the life of the forging is predicted by calculating the damage under alternating stress. This method is suitable for the case of constant amplitude alternating stress.
Local stress strain method: Considering the local stress and strain distribution of forgings under alternating stress, combined with the cyclic stress-strain curve of materials and damage accumulation theory to predict its life. This method is suitable for varying amplitude alternating stress and complex stress states.
Fracture mechanics method: Based on crack propagation theory and fracture toughness parameters, the life of forging is predicted by calculating the life of crack propagation. This method is suitable for cases where there are initial cracks or defects.
Probabilistic statistical method: The fatigue data of a large number of similar forgings are processed and analyzed by statistical method, and the statistical model of life distribution is established to predict the life of forgings. This method can take into account the influence of various uncertainties on the life span.
Fatigue performance and life prediction of petrochemical forgings is one of the key links to ensure the safety and longevity of equipment. The research on fatigue performance and influencing factors of petrochemical forgings and the effective prediction method can provide scientific basis for equipment maintenance and replacement, and reduce safety risks and economic losses. With the emergence of new materials and new technologies, the fatigue performance and life prediction of petrochemical forgings will face more challenges and opportunities in the future. Relevant enterprises and researchers need to constantly explore and innovate to adapt to changes in market demand and contribute to the sustainable development of the petrochemical industry.
