Fatigue or corrosion fatigue is a common form of failure in industrial production equipment, and this phenomenon is more prominent in the petrochemical industry. So, how to avoid corrosion fatigue failure of centrifugal compressor impeller? Recently, Hefei General Machinery Research Institute relied on the degradation mechanism of key compressor components and key life extension technologies under the conditions of the "973" project to conduct an in-depth study on the corrosion fatigue problem of the impeller, a key component of centrifugal compressors in the petrochemical industry, and clarified the corrosion fatigue failure mechanism. , occurrence and development rules.
Fatigue is a phenomenon in which materials or components suddenly break under cyclic loading. Examples of fatigue damage are common in daily life, such as the front fork of a bicycle suddenly breaking while driving, a pickaxe splitting into two when digging the ground, and a steel wire breaking when folded in half, etc. People have this experience in daily life. If you choose to fold the steel wire in half where it is rusty (corroded), the steel wire will be easier to break. It can be seen that corrosion damage will promote fatigue damage.
The same situation will happen in the petrochemical industry. Hefei General Machinery Research Institute found through investigation that many failure accidents of centrifugal compressors in the petrochemical industry are closely related to corrosion fatigue, such as the breakage of air compressor impellers in petrochemical enterprises and the cracking of the impellers of rich gas compressors in catalytic devices. In the current production of petrochemical enterprises, the corrosion fatigue problem of impellers has become one of the main failure modes restricting the long-term safe operation of centrifugal compressor units.
Why is the impeller of centrifugal compressor prone to corrosion fatigue? The research group on the deterioration mechanism of key components of compressors and key life extension technologies under the conditions of Hefei General Machinery Research Institute explained that during high-speed rotation, the impeller not only bears cyclic loads such as variable speed centrifugal force and air flow disturbance force, but also has corrosion effects. Direct contact with the permanent process medium, the combined effects of cyclic loading and corrosion contribute to the corrosion fatigue failure of the impeller.
The subject studied the fatigue behavior of the impeller in medium environments such as air, water mist, salt mist and hydrogen sulfide at different temperatures. Taking the fatigue of impeller material FV520B steel in a salt spray environment as an example, the damage process consists of pitting pits forming and growing, cracks starting from pitting pits and expanding until they break. In the early stages of the corrosion fatigue process, pitting pits are easily generated and gradually grow at the locations of microscopic defects on the material surface or uneven electrochemical properties caused by fatigue damage. When the pitting pit grows to the critical size for crack initiation, a crack will appear at this location, and then the crack will gradually expand until it breaks. The time required for the formation and growth of pitting pits, initiation and expansion of cracks, etc. is the corrosion fatigue life, which depends on the joint action of service temperature, stress level, chemical corrosion and other factors.
On the basis of clarifying the fatigue failure mechanism, occurrence and development rules, through a large number of theoretical analysis and experimental tests, and comprehensively considering the joint effects of the stress field, temperature field and chemical field, the research team established the corrosion fatigue life prediction of the compressor impeller. method. At present, this method has been applied in the traceability of failure accidents of rich gas compressors, circulating hydrogen compressors, and air compressor impellers. For example, for the air compressor of the olefin division of a petrochemical enterprise, the corrosion fatigue research results were used to analyze the impeller/blade The causes of failure and fracture were found, the key influencing factors of failure were found, and in-service maintenance suggestions were put forward to prevent the formation of pitting corrosion and extend fatigue life, which provided a scientific basis to avoid the recurrence of similar accidents.
It is reported that the research results have also been applied in the design of new compressor products. For example, for the mechanical vapor recompression system for salty sewage treatment, in the early stages of compressor design and manufacturing, full consideration was given to the possible presence of high concentrations of salt, In the water vapor environment, through impeller corrosion fatigue life analysis and structural design improvement, the life reliability of the compressor has been improved, laying a good foundation for long-term safe service in the future. In the future, this achievement will also be promoted in in-service remanufacturing of compressors. Through impeller damage assessment and remaining life analysis, the service life of the compressor can be reasonably extended while ensuring safety, thereby achieving the purpose of life extension.
