As a key component in pipeline systems for absorbing displacement and mitigating vibration, the performance of expansion joints directly affects the safety and operational stability of the pipeline network. To ensure their reliable operation during service, a systematic assessment of their structural integrity, compensation capacity, and connection reliability must be conducted according to a scientific and standardized inspection process. Inspection work includes both routine appearance and dimensional checks, as well as specialized performance tests and non-destructive testing, and must be continuously carried out at different stages and throughout the production, installation, and operation cycles.
The inspection process typically begins with preliminary preparation. The purpose of the inspection and the applicable standards and specifications should be clearly defined. Product technical data, design parameters, and previous inspection records should be collected, and technical indicators such as the working medium, design pressure and temperature, and compensation amount should be confirmed. Based on the type of expansion joint and the operating environment, a plan should be developed that includes inspection items, methods, instruments, and judgment criteria. Safety protection and work permits should be implemented, especially for pipelines transporting flammable, explosive, or toxic media, where isolation and replacement measures must be taken in advance to ensure the safety and controllability of the inspection process.
Appearance and dimensional inspection are fundamental steps. The outer surface of the bellows must be inspected for cracks, pits, folds, corrosion spots, or mechanical damage. Welds and connections to end pipes should be free of defects such as porosity, incomplete fusion, or undercut. Use measuring tools to verify critical dimensions, including effective length, corrugation pitch, corrugation height, and the outer diameter and thickness of the flange or end pipe, ensuring they are within allowable tolerances. For expansion joints with flange connections, check the flatness and roughness of the sealing surface, and confirm that the gasket type and installation condition meet requirements.
A sealing test is used to verify the reliability of the connection. This is typically done using hydrostatic or pneumatic methods, maintaining pressure at a specified time and observing pressure drop and leakage. The test medium should be similar to or more permeable to the operating conditions to improve detection sensitivity. For high-pressure or large-diameter expansion joints, pressure can be increased in stages, and pressure changes recorded at each stage to detect potential micro-leakage.
Non-destructive testing is used for parts that cannot be directly observed. Common methods include radiographic testing (RT), ultrasonic testing (UT), and magnetic particle testing (MT) to detect defects such as cracks, inclusions, and incomplete penetration within bellows and welds. The testing area should cover the longitudinal and circumferential seams of the bellows, as well as the mating area with the end pipes. The evaluation results must meet the corresponding standard's acceptable level.
Compensation performance testing is conducted on a qualified testing bench. By applying axial, lateral, or angular displacement, the actual compensation and residual deformation of the expansion joint are measured and compared with the design values to verify its flexibility and recovery capability under set operating conditions. For expansion joints equipped with guiding and limiting devices, the guiding accuracy and the effectiveness of the limiting function should be tested simultaneously.
After testing, a report must be prepared, detailing the testing conditions, instruments and equipment, process data, and judgment conclusions. Suggestions for rectification or scrapping should be made for non-conforming items, and the results of re-inspections should be tracked. During operation, retesting should also be conducted periodically based on online monitoring data to form a periodic evaluation mechanism.
In summary, the expansion joint inspection process is mainly based on preparation, appearance and size inspection, sealing test, non-destructive testing and performance verification. Each step is closely linked and the standards are clear. Only by strictly implementing the process can potential problems be identified in a timely manner and the long-term stable operation under complex working conditions be guaranteed.