The quality assurance of metallic expansion joints in bellows systems involves a series of rigorous testing and inspection processes.
I. Visual Inspection
· Purpose: To initially assess the overall quality and integrity of the expansion joint.
· Steps: Inspectors visually examine the surface of the expansion joint for any obvious scratches, dents, or rust. They also confirm the regularity of the corrugation shape and check for any deformation or damage.
II. Dimensional Measurement
· Purpose: To ensure the expansion joint can be correctly installed in the piping system.
· Tools: Precision measurement tools such as calipers or micrometers are used.
· Measurements: Include corrugation height, pitch, and overall length of the expansion joint, which should match the design drawings or product specifications.
III. Material Analysis
· Purpose: To check the material composition, mechanical properties, and other requirements of the bellows.
· Equipment: Metallurgical microscope, tensile testing machine, etc.
IV. Non-Destructive Testing (NDT)
· Purpose: To detect any internal defects in the bellows.
· Methods: According to international or industry standards such as EJMA or ASME, NDT methods such as liquid penetrant testing (LPT) or radiographic testing (RT) are employed.
V. Performance Testing
1. Pressure Testing
· Purpose: To verify the performance of the expansion joint under a certain pressure.
· Steps: Conduct hydrostatic or pneumatic testing at a specified multiple of the design pressure (e.g., 1.5x or 1.3x) and observe for any leaks or deformations.
2. Leak Testing
· Purpose: To check for leaks in the expansion joint.
· Steps: Under a specific pressure, use detection devices to observe for any gas leaks.
3. Fatigue Testing
· Purpose: To assess the service life of the expansion joint.
· Steps: Simulate long-term deformation conditions and subject the expansion joint to fatigue testing, recording its deformation and lifetime.
VI. Durability Assessment
· Purpose: To predict the lifespan and performance of the expansion joint in actual use.
· Methods: Conduct accelerated aging tests or simulate harsh environmental conditions to evaluate the corrosion resistance, wear resistance, and fatigue resistance of the expansion joint.
VII. Sampling Rules and Coverage
· Sampling Rules: Randomly select samples for type testing from products with the same design method, raw material grade, manufacturing process, and specifications.
· Coverage: Ensure comprehensive and accurate testing by covering aspects such as bellows type, size, pressure rating, and displacement capacity.
