Discussion on Notification and Inspection Issues for Pressure Vessel Nozzle Replacement
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TSG21-2016 “Safety Technical Inspection Regulations for Fixed Pressure Vessels”, which came into effect on October 1, 2016, clearly defines the conceptual scope and basic requirements regarding major repairs of pressure vessels. Inspection personnel should thoroughly understand and master the key aspects and items to be inspected during on-site supervision of major repairs of pressure vessels, so as to ensure the quality of such inspections. Major repairs of pressure vessels generally refer to the replacement, reshaping, or patching of pressure-bearing components, as well as the weld repair of Type A and Type B butt joints in pressure vessels manufactured by welding (the classification of Type A and Type B butt joints in pressure vessels is usually based on the relevant provisions of national standard 150), or the repair of bonded parts in non-metallic pressure vessels. Question 1: The equipment belongs to the category of pressure vessels with a jacket, and the medium used in the jacket is hot water or circulating water. Currently, the pipes at the connection point between the jacket and the inner cylinder have diameters of DN150 and DN250, and these need to be replaced. Is it necessary to inform the relevant authorities about this repair work? Is supervision and inspection by a specialized inspection agency required? Question 2: The standard requires written notification only when major repairs are carried out on the main pressure-bearing components, and these components are those with a diameter of DN250 or larger. Can it be understood that no notification is required, nor is any inspection necessary, for components with a diameter smaller than DN250? The jacket can be said to be outside the scope of pressure vessels, with only the inner cylinder being under pressure. Discussion 1: The standards are rather general. In my opinion, although the nominal size of the replacement fittings may not meet the requirements of the main pressure-bearing components, construction will still have an impact on the main shell (head, cylinder), so it is necessary to provide information and carry out supervision and inspection. Question 3: Is it necessary to provide notification and conduct inspection for the repair of the surfacing layers on the primarily stressed components as well as those on the main weld joints? Discussion 2: Due to differing interpretations of the standards, it is necessary to provide prior notification and seek the opinions of the quality supervision bureau and the special inspection agencies. If they deem it unnecessary, no further monitoring inspections will be carried out to avoid omissions.
Question 1: According to the provisions of the TSG21-2016 standard, for major repairs of pressure vessels, whether it involves replacing, reshaping, or patching stressed components, or welding or repairing non-metallic vessels, notification of the repair work is required, as well as supervision and inspection by a specialized inspection agency. Therefore, if the sleeve at the junction between the jacket and the inner cylinder needs to be replaced, modification, repair notification, and supervisory inspection are also required. Question 2: According to the standards, major repairs to primary pressure components require written notification, and a primary pressure component is defined as one with a diameter of DN250 or greater. The jacket can be considered an attachment and is not part of the pressure vessel; only the inner cylinder is under pressure. Therefore, in theory, the replacement of jackets below DN250 does not require notification or inspection. However, since the construction affects the main housing, to ensure safety, it is recommended to carry out notifications for renovation and maintenance as well as supervision and inspection. Question 3: Notification and supervision are also required for the repair of the surfacing layers on the primarily stressed components as well as those on the main welded joints. This is because repairing the surfacing layer or weld joint may affect its strength and sealing performance, factors that are crucial for the safety of pressure vessels. Discussion 2: Due to differing views on the standards, it is recommended to first submit a notification for renovation and repair, and then decide whether further inspection is necessary based on the opinions of the quality supervision agency and the special inspection authorities. This helps to avoid omissions and ensures the completeness and security of the work. .
According to the standard procedures, the outer cylinder does not require such notification, while the inner cylinder does. However, in the case of replacing the pipe connections, there is no need for such notification – the cost involved is too high. It’s sufficient to find a skilled welder to carry out the welding work oneself; no notification is required, as it would lead to too many problems later on.