The groove issue of end caps
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If the head of the pressure vessel is purchased from an external supplier, and it is required that a notch be machined in the head during its fabrication, should this notch be made as an external groove or an internal groove?
During the procurement of end caps, whether to use external or internal bevels for processing is mainly determined by the diameter of the container; if it is possible for people to enter the container, it is better to use internal bevels, otherwise external bevels should be used. Welding procedure qualification is also required to support this decision.
The groove preparation for the end cap must be determined based on the welding process; the weld pattern between this end cap and the butt-welded cylinder must be consistent. Therefore, when ordering the end cap, its groove shape should be determined by referring to the groove shape of the corresponding cylinder.
The groove processing for the end cap must be consistent with the weld pattern used for joining it to the cylindrical shell; therefore, when ordering the end cap, its groove pattern should be determined based on the groove pattern of the shell
What the original poster means is to order the end cap first, and then fabricate the grooves on the cylinder body according to the shape of those grooves on the end cap. If it’s not possible to get inside, an external cut can be made and TIG welding can be used for the root pass while manual welding is used for the finish layer; if access is possible, double-sided grooves can be created
According to our regulations, when welding the head to the cylinder, if the nominal diameter DN is ≥ 600, an internal groove must be provided on the head； When the nominal diameter DN is < 600, an external groove is provided on the head
The groove of the head is determined by the welding process, which in turn is determined by the thickness, diameter, material of the head, as well as the structure of the container. Therefore, before purchasing the head, provide the part drawings for the head first; the head manufacturer can then make the grooves based on those drawings.
It seems that the internal groove format is the preferred choice, but why is the internal bevel preferred?
Volumes 20580-20585 in combined form; 333 is also available. For values less than 600, an external groove is used for welding, while for values greater than 600, an internal groove is used. Why is an internal groove used? It’s because during internal welding, under pressure, the weld seam tends to close. If the external groove weld is open, it is not subject to sufficient stress; any defects in such a weld can lead to problems... (personal understanding)
The owner’s specifications generally state that we simply need to carry out the processing as required by the owner. Our company usually creates external notches for this purpose; although internal notches offer advantages in terms of stress distribution and other factors, external notches are preferable due to the ease of welding work
When ordering a head, it is necessary to provide the groove type of the head to the manufacturer