After piping is prefabricated, quality inspection is an important step to ensure that the piping assembly complies with design and construction specifications. Comprehensive quality inspection includes visual inspection, dimensional inspection, weld inspection, pressure test and non-destructive testing, etc. The following describes in detail the various quality inspection steps after pipeline prefabrication.
1. Appearance inspection
1.1 Check content
Surface condition: Check the surface of the pipe for scratches, pits, cracks and other defects.
Anti-corrosion coating: Check the uniformity and integrity of the anti-corrosion coating to ensure there are no problems such as shedding or blistering.
Cleanliness: Check whether the internal and external surfaces of the pipe are clean and free of oil, dust and other impurities.
1.2 Inspection method
Visual inspection: Visually observe the pipe surface to detect obvious defects and problems.
Touch inspection: Through hand inspection, problems such as insufficient smoothness and unevenness of the surface are found.
Appearance inspection is the first level of quality control. Obvious defects on the pipe surface can be quickly discovered through visual and touch inspection. These defects may affect the subsequent use of the pipeline, so problems need to be dealt with promptly when discovered.
2. Dimensional inspection
2.1 Check content
Length and diameter: Measure the actual length and diameter of the pipe to ensure it meets design requirements.
Angle and curvature: Check the bending angle and curvature of the elbow to ensure it complies with the design drawings.
Flange parallelism and perpendicularity: Check the flange parallelism and perpendicularity to ensure sealing performance after installation.
2.2 Inspection methods
Steel tape measure: Used to measure the length and outer diameter of pipes.
Protractor and Template: Used to measure the angle and curvature of bent pipes.
Ruler and level: used to measure the parallelism and perpendicularity of flanges.
Dimensional inspection ensures that prefabricated duct assemblies are dimensionally consistent with design specifications. Using precision measuring tools, you can ensure that the dimensions of every pipe component are within tolerances, which is critical to the installation and use of pipes.
3. Weld inspection
3.1 Check content
Weld appearance: Check whether the weld is flat and uniform, and whether there are any defects such as pores, cracks, and slag inclusions.
Weld size: Measure the width and height of the weld to ensure it meets design requirements.
3.2 Inspection method
Visual inspection: Obvious welding defects are found by visually observing the weld surface.
Weld gauge: used to measure the size of welds to ensure compliance with design requirements.
Dye Penetrant Inspection: Use dye penetrant to detect tiny cracks and defects on the surface of the weld.
Weld inspection is a critical step to ensure welding quality. Various defects are prone to occur during the welding process. Through methods such as visual inspection and dye penetrant testing, these defects can be effectively discovered and repaired to ensure the reliability of the weld.
4. Stress testing
4.1 Hydrostatic test
Purpose: To verify the pressure-bearing capacity and sealing performance of the pipeline.
Step:
Mount the piping assembly on the test bench and seal all openings.
Inject water into the pipeline through a pressure pump and gradually increase the pressure to the design pressure.
Maintain the design pressure for a period of time and observe whether there are leaks or deformations in the pipes and welds.
Qualification standards: No leakage or obvious deformation within the specified time, and the pressure drop is within the allowable range.
4.2 Air pressure test
Purpose: To check the air tightness of pipelines, suitable for specific medium transportation pipelines.
Step:
Seal the piping assembly and fill with dry air or nitrogen.
Gradually increase the pressure to the design pressure and maintain it for a period of time.
Use soapy water or a leak detector to check for air bubbles at joints and welds.
Qualification standard: no bubbles appear within the specified time, and the pressure drop is within the allowable range.
Pressure testing is an important step to verify the pressure-bearing capacity and sealing performance of pipelines. Through hydraulic pressure testing and air pressure testing, the safety and reliability of pipelines in actual use can be ensured.
5. Non-destructive testing
5.1 Ultrasonic testing
Purpose: To detect internal defects of welds, such as cracks, pores, slag inclusions, etc.
Step:
An ultrasonic probe is used to scan along the surface of the weld, and the ultrasonic waves emitted by the probe produce reflected signals when encountering defects.
Observe the reflected signal through the instrument display screen to determine the location and size of defects inside the weld.
Qualification standard: There are no major defects inside the weld, and the size and number of defects are within the allowable range.
5.2 Ray detection
Purpose: to detect internal defects by penetrating welds with X-rays or gamma rays.
Step:
Place the ray source and detector on both sides of the weld.
By rays penetrating the weld, the detector records the intensity change after the rays penetrate.
Analysis of internal defects in welds from radiographic film or digital images.
Qualification standard: There are no major internal defects in the weld, and it meets the design and specification requirements.
Non-destructive testing is a high-tech means to ensure the quality of welds. Through ultrasonic testing and radiographic testing, defects within the weld can be detected non-destructively, providing reliable quality assurance.