Annual inspection issues for pressure pipelines in the inner tube of a jacketed tube

I. Issues regarding the annual inspection of the inner tube in a double-pipe jacket structure: In cases where there is a double-pipe jacket structure, if the inner tube is considered a pressure pipeline, it is also required to undergo regular inspections as per regulations. Since the outer tube is wrapped on the outside, conventional inspection methods (such as visual inspection and ultrasonic testing) are limited; it is neither necessary nor possible to cut through the entire outer tube for inspection. Standard practice: 1. Without damaging the outer tube, conduct a local inspection using methods such as an endoscope or radiographic testing (RT) at the port or interface that is easier to access ； 2. If no suitable access point is available, consider reserving an inspection port/detection hole during design to facilitate non-destructive testing ； 3. Regularly monitor the pressure, temperature of the media inside and outside the pipes, as well as any leaks, in order to assist in assessing the condition of the pipes, rather than conducting thorough weld inspections every time. In practice, it is generally not necessary to completely cut open the outer tube just for testing, as this is costly and impractical. Most use endoscopic inspection, local X-ray, ultrasonic testing (UT), or other alternatives. II. Whether the outer tube is a pressure pipeline: Whether the outer tube of a jacketed tube is a pressure pipeline depends on the medium being transported, the design pressure, temperature, and the hazardous properties of the medium. If the medium inside the outer tube meets the criteria for classification as a pressure pipeline (such as a medium pressure of ≥0.1 MPa, being toxic, harmful, flammable, explosive, corrosive, or operating under high temperature and pressure conditions), then the outer tube must be submitted for approval and registration as a pressure pipeline, and shall fall under the supervision framework for special equipment safety. In summary: - When the inner pipe is a pressure pipeline, specific testing methods must be employed to prevent overall failure. - When the medium and conditions inside the outer tube meet the requirements of pressure pipeline standards, the outer tube shall also be approved, registered, and inspected as a separate pressure pipeline, and subject to regular inspection and management. .