Cracks and preventive measures during pressure vessel and pressure piping inspection

1. Inspection Content and Methods
When inspecting pressure vessels and pressure piping, common methods include hydrostatic testing and external and internal inspections. When inspecting pressure vessels, inspectors must carefully check the equipment supports, manufacturer, protective devices, and appearance. Furthermore, spot checks should be conducted on weld flaw detection and safety. When inspecting the exterior, inspectors should pay close attention to the routing and insulation of the pipelines and platforms. When inspecting pressure piping, they should also promptly check the expansion conditions, technical documentation, and the quality of the installed piping, while also conducting hydrostatic testing. Furthermore, inspectors should closely monitor the drainage and drainage of pipes. When conducting external inspections, pressure vessels must be kept in working condition and inspected at least annually. It is important to note that inspectors should inspect the exterior of the vessel upon initial use and upon restarting after one year of inactivity. Any major modifications to the pressure vessel require a prompt exterior inspection. Internal inspections should be conducted when the vessel is out of service and at least every two years. Internal inspections are typically conducted after a special situation occurs during the operation of a pressure vessel. During the inspection, the vessel's internal tightness and safety must be thoroughly verified. Generally, a hydrostatic test is required every six years, but it should not be conducted simultaneously with the internal inspection. Any problems encountered during the hydrostatic test will render the pressure vessel inoperable after the inspection is completed.

2. Cracks Generated During Pressure Vessel Operation

Based on industry experience, fatigue cracks are a common cracking problem during later operation. These can be further categorized into mechanical fatigue cracks and corrosion fatigue cracks based on their causes. Mechanical fatigue cracks are mostly caused by uneven stress. Initial cracks are relatively small, but they gradually enlarge over time, requiring technicians to focus on stress points. Corrosion cracks arise from damage caused by corrosive materials in the pipeline, combined with uneven pressure distribution in the pipeline. These two factors contribute to the development of mechanical cracks into corrosion cracks. Unlike mechanical cracks, which tend to gradually widen, these cracks tend to lengthen over time and with long-term use. Once a crack occurs in a pipeline, it's extremely difficult to address, requiring significant investment in both capital and personnel, as well as significant time and effort. Therefore, rather than resorting to remedial measures after a crack has formed, it's better to prevent it before it occurs.