Safety Assessment of Pressure Pipelines
Posted: 01/06/2022 02:48:12 Hits: 21
Reducers
A reducer is an important part of the pressure pipeline, which is a common component for connecting pipelines in petroleum and petrochemical equipment. It is mainly used for connecting two pipes with different diameters. A reducer can change the pipe diameter, adjust the flow rate of the medium, change the direction of the pipeline or increase the flexibility of the pipeline to alleviate the stress of the pipeline. It is one of the indispensable pipeline components in the pipeline and is frequently used in pipeline systems. Compared with straight pipes and equal elbows, the geometry of reducers is more complicated. The size of the cross-sectional structure of the reducer along the axial direction is constantly changing, and the effect of external load F will produce stress concentration. At the same time, the stress distribution is complicated due to the force and bending moment generated by factors such as scouring of media, expansion caused by heat and contraction caused by cold. It becomes one of the weakest parts of the pipeline.
Reducers are more and more widely used in industrial pressure pipelines and equipment, and many accidents have occurred in the use. On January 1, 1984, a pipeline with a diameter of 300 mm between the de-propanizer and the bottom reboiler of a gas separation plant in a certain factory was found to be broken at the welded joint of a reducer, causing the leakage of propane, a fire and an explosion. A serious accident caused many casualties, and the direct economic loss was as high as 2.52 million RMB. The partial stress increases and becomes a potential source of hazard in the pipeline due to the change of the pipe's diameter. Assessing its safety in production and use is of great significance for safe production.
Welding technology is often used to connect straight pipes and reducers. There will be inevitable various defects with different types and shapes after the welding is completed due to the limitation of welding conditions and on-site environment, causing hidden dangers in production safety. In order to ensure the safe operation of the equipment, it is necessary to analyze and evaluate the safety of the pipe and pipe fitting. At present, the relevant domestic standard doesn't provide corresponding analysis and evaluation methods for reducers. Looking up the literature, there are few related reports. Most of them are related analysis and safety assessment for defects of the straight pipe section or the pipe fitting. Therefore, the research on the stress and ultimate load analysis of the connecting structure of the reducer and straight pipe has become an urgent issue to be solved.
The research situation of safety assessment of pressure pipelines abroad
From the 1970s, Western developed countries began to carry out relevant researches on the safety assessment of pressure pipelines. The United States has successively launched the The Research Project of Degraded Pipes and the Research Projects on Short Cracks in Pipelines and Welding Seams of Pipelines. The Research Projects of Degraded Pipes is used to establish and improve the ultimate load and fracture mechanics analysis methods for the leakage of nuclear pipelines before they are broken. The experiment mainly includes properties of materials, fracture of pipes and evaluation methods of fracture. The plan verified ASME XI IWB-3650 Research Projects on Short Cracks in Pipelines and Welding Seams of Pipelines and improved the evaluation method for large-diameter pipes with short circumferential cracks. The effect of pipeline ovalization on J Integration and limit loads of pipelines under various loads was proposed. Fracture test databases of the longitudinal cracked pipeline and the circumferential cracked pipeline were established. The German National Nuclear Industry Safety Committee first studied the strength and crack expansibility of elbows, straight pipes and tees or branch pipes under the effect of various loads. On the basis of this, two major criteria, that is, basic safety criteria and fracture prevention evaluation criteria were proposed. Japan began to study the safety evaluation of pressure pipelines in the 1970s, and the research included fatigue experiments, fracture experiments and destructive experiments of pressure pipelines, covering almost all fields related to pressure pipelines.
The situation of the safety assessment research on domestic pressure pipelines
The research on pressure pipelines started late in China, so in the process of compiling and researching the safety assessment standards for defective pressure pipelines, it is often based on the relevant standards of the Western countries and the United States.
The research on the defect assessment technology of pressure vessels began in the 1970s. A large number of practical researches have been completed in about 10 years, and a rich engineering practical experience has been accumulated, providing a solid foundation for safety assessment standards for defects of pressure vessels. Finally, at the end of 1984, the Evaluation Specifications of Defects of Pressure Vessels CVDA-84 was published. It represented the highest level of relevant research in China at that time, and compared with the relevant international evaluation standards, it had a certain degree of advancement. It was a relatively conservative evaluation method. After years of research and exploration, GB/T 19624-2004 Safety Assessment of Pressure Vessels with Defects in Use was launched in 2004.
A reducer is an important part of the pressure pipeline, which is a common component for connecting pipelines in petroleum and petrochemical equipment. It is mainly used for connecting two pipes with different diameters. A reducer can change the pipe diameter, adjust the flow rate of the medium, change the direction of the pipeline or increase the flexibility of the pipeline to alleviate the stress of the pipeline. It is one of the indispensable pipeline components in the pipeline and is frequently used in pipeline systems. Compared with straight pipes and equal elbows, the geometry of reducers is more complicated. The size of the cross-sectional structure of the reducer along the axial direction is constantly changing, and the effect of external load F will produce stress concentration. At the same time, the stress distribution is complicated due to the force and bending moment generated by factors such as scouring of media, expansion caused by heat and contraction caused by cold. It becomes one of the weakest parts of the pipeline.
Reducers are more and more widely used in industrial pressure pipelines and equipment, and many accidents have occurred in the use. On January 1, 1984, a pipeline with a diameter of 300 mm between the de-propanizer and the bottom reboiler of a gas separation plant in a certain factory was found to be broken at the welded joint of a reducer, causing the leakage of propane, a fire and an explosion. A serious accident caused many casualties, and the direct economic loss was as high as 2.52 million RMB. The partial stress increases and becomes a potential source of hazard in the pipeline due to the change of the pipe's diameter. Assessing its safety in production and use is of great significance for safe production.
Welding technology is often used to connect straight pipes and reducers. There will be inevitable various defects with different types and shapes after the welding is completed due to the limitation of welding conditions and on-site environment, causing hidden dangers in production safety. In order to ensure the safe operation of the equipment, it is necessary to analyze and evaluate the safety of the pipe and pipe fitting. At present, the relevant domestic standard doesn't provide corresponding analysis and evaluation methods for reducers. Looking up the literature, there are few related reports. Most of them are related analysis and safety assessment for defects of the straight pipe section or the pipe fitting. Therefore, the research on the stress and ultimate load analysis of the connecting structure of the reducer and straight pipe has become an urgent issue to be solved.
The research situation of safety assessment of pressure pipelines abroad
From the 1970s, Western developed countries began to carry out relevant researches on the safety assessment of pressure pipelines. The United States has successively launched the The Research Project of Degraded Pipes and the Research Projects on Short Cracks in Pipelines and Welding Seams of Pipelines. The Research Projects of Degraded Pipes is used to establish and improve the ultimate load and fracture mechanics analysis methods for the leakage of nuclear pipelines before they are broken. The experiment mainly includes properties of materials, fracture of pipes and evaluation methods of fracture. The plan verified ASME XI IWB-3650 Research Projects on Short Cracks in Pipelines and Welding Seams of Pipelines and improved the evaluation method for large-diameter pipes with short circumferential cracks. The effect of pipeline ovalization on J Integration and limit loads of pipelines under various loads was proposed. Fracture test databases of the longitudinal cracked pipeline and the circumferential cracked pipeline were established. The German National Nuclear Industry Safety Committee first studied the strength and crack expansibility of elbows, straight pipes and tees or branch pipes under the effect of various loads. On the basis of this, two major criteria, that is, basic safety criteria and fracture prevention evaluation criteria were proposed. Japan began to study the safety evaluation of pressure pipelines in the 1970s, and the research included fatigue experiments, fracture experiments and destructive experiments of pressure pipelines, covering almost all fields related to pressure pipelines.
The situation of the safety assessment research on domestic pressure pipelines
The research on pressure pipelines started late in China, so in the process of compiling and researching the safety assessment standards for defective pressure pipelines, it is often based on the relevant standards of the Western countries and the United States.
The research on the defect assessment technology of pressure vessels began in the 1970s. A large number of practical researches have been completed in about 10 years, and a rich engineering practical experience has been accumulated, providing a solid foundation for safety assessment standards for defects of pressure vessels. Finally, at the end of 1984, the Evaluation Specifications of Defects of Pressure Vessels CVDA-84 was published. It represented the highest level of relevant research in China at that time, and compared with the relevant international evaluation standards, it had a certain degree of advancement. It was a relatively conservative evaluation method. After years of research and exploration, GB/T 19624-2004 Safety Assessment of Pressure Vessels with Defects in Use was launched in 2004.
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