During the operation of a thermal power unit’s high-pressure bypass （HPB） system， excessive vibration caused the breakage of the attached pressure-tapping tube. After the vibration reduction modification， it is required to analyze the vibration alternating stress level of the pressure-tapping tube and assess its safety. To this end， the vibration alternating stress level at the cracked location of the pressure-tapping tube is measured by the strain test method under the change of differential pressure and opening degree before and after the high-pressure bypass valve. The relationship between the vibration alternating stress magnitude of the pressure-tapping tube and the differential pressure before and after the high-pressure bypass valve and its opening degree is analyzed. The critical operating parameters for the potential fatigue fracture of the pressure-tapping pipelines are given： when the opening degree of the high-pressure bypass valve is 35%， and its differential pressure exceeds 3.70 MPa， the fatigue fracture of the pressure-tapping tube may occur. Finally， it is concluded through analysis that the high-pressure bypass vibration mainly comprises high-frequency vibration due to the high-frequency acoustic energy， which excites and amplifies the high-frequency vibration on the pipeline wall.
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