Pressure vessel opening nozzle structures, inserted and non-inserted types

1. Insertion type nozzles are generally constructed using fillet welds or corner butt combination welds; they experience relatively high stress concentration, but are easy to manufacture, convenient to install, and allow for thorough welding； It is commonly used in medium and low-pressure equipment. 2. Fixed-type fittings have better stress resistance compared to inserted-type ones; they also offer higher machining precision, smaller openings. The reduction factor is 1.0, resulting in a smaller area that needs to be reinforced. However, ultrasonic testing is required at the opening site, and drilling may be necessary. Fittings are often made from forged materials, which makes processing more difficult and increases costs, but the quality is guaranteed. It is generally used in high-voltage equipment. 3. Embedded takeover is commonly used in fatigue vessels and spherical tanks, where high requirements are placed on the quality of weld joints. Since the weld joint is a Class A joint, the inspection requirements are high, which increases the manufacturing cost. 4. The purpose of boring after welding is to ensure the alignment of the holes in the pipe joint. For example, regarding the selection of the structure below: 5. Challenges in achieving the embedded structure in actual production: a. It is very difficult to remove defects such as incomplete welding and undercut on the inner surface through mechanical cutting; the operation is complicated, and it is not easy to inspect tubes with small diameters. b. For areas with large curvature changes, socketed fittings are used; it is difficult to achieve a perfect (three-dimensional) fit between the end face of the fitting (especially when the pipe diameter is large) and the surface it is fitted to, that is, to have no gaps. 6. The comparison between fixed and insert-type connectors should be based on a fully weld-through structure. For structures that do not require full penetration (usually a type of container), an insert-type method is more convenient. I think the plug-in structure is more suitable in the following situations: 1) there are reinforcement plates; 2) root cleaning and double-sided welding are possible; 3) the shell thickness is not too great. The embedded structure is more suitable for nozzles with small diameters on thick-walled vessels, as well as for structures that cannot be welded on both sides and for which the use of welding gussets is not permitted. For small-diameter security structures, the connection surface of the pipe fittings can also be made flat; a shallow flat counterbore is created in the housing to facilitate positioning and assembly as well as the machining of the pipe fitting connection surface. The saddle-shaped welding groove at the takeover end face is difficult to machine. Not all fixed-type structures require internal boring; single-sided welding with double-sided formation usually ensures full penetration, and after welding, it is sufficient to properly grind the inside of the pipe fitting. If it is considered unreliable and a suitable boring machine is available, post-weld internal boring can also be used; of course, the efficiency in this case is relatively low. 7. For the fixed-type housing, there should be no delamination in the steel plate section at the opening. To achieve this, ultrasonic testing (UT) is required within a range of twice the diameter of the opening. Because the fixed-type fitting is welded to the surface of the steel plate, any fitting is subjected to an axial force under internal pressure. If there is a layering structure below, the steel plate will tear under the action of axial forces. After tearing, the thickness of the steel plate is no longer the original thickness; once the thickness decreases, the strength will no longer meet the requirements.

It has been explained in detail upstairs; generally, the fixed-type installation is suitable for small-diameter connections, those on high-pressure vessels with thick vessel walls. Small connections on flat covers together with threaded fittings are often used in such cases

Refer to Appendix D of GB150.3, which describes plug-in nozzles, embedded nozzles, and fixed nozzles; it provides information on their specific structural forms and areas of application

I still don’t quite understand it; I’ll just keep learning slowly*

Medium and low-pressure vessels often use plug-in nozzles...