The combination of pvelite’s nozzles will bring disaster

A long time ago, the company received a Japanese project, the equipment is designed according to ASME, because the company has only one point, for the sake of efficiency, I am responsible for the calculation of all equipment.
After the calculation, the thickness of the equipment is calculated and the dimensions are marked to the designer.
The equipments in the project are horizontal stainless steel tanks with low internal pressure and full vacuum negative pressure, which are basically 6 mm ~ 8 mm. By choosing the right reinforcing ring, the wall thickness and reinforcement can be controlled to the minimum.

There are a lot of equipment. For convenience, many of the same nozzles are combined.

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After the calculation is completed, the drawing calculation sheet will be sent to the owner for approval.
Many friends can understand that for the sake of project progress, many projects of manufacturing units are synchronized with design and procurement construction, and they will not wait until the design is completely completed before purchasing materials, especially the main materials – cylinder and head. The cycle is relatively long, so we should go ahead.
Therefore, at the same time of issuing the drawings to the owner, the manufacturing process makes the main materials of the drawings as antecedents and orders them first. Although there are appropriate risks, generally speaking, the calculation of the main materials will not have any problems. Generally speaking, it is not a big problem.
Here’s the problem
After two weeks, the owner’s comments on the drawings and calculations returned. There is one item in the calculation sheet:
The nozzle should be built separately according to the location and orientation of the owner.
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After the nozzle is established according to the actual position, two identical manholes are found, one of which can pass the calculation and the other is unqualified.
Scared to sweat, the plate has been ordered, this equipment 304 materials, the calculation of the required thickness of 7.9MM, the actual purchase of 8mm, the reinforcement ring has been used to the largest, if you want to thicken the cylinder, it will cause a very big loss.

Reason

After checking the calculation sheet, it turns out that due to structural reasons, the stiffening ring was placed in the center of the equipment at first, and then there was a connecting pipe in the center, so the stiffening ring was placed 1400mm away from the left end weld of 3M long cylinder.
When the connecting pipe is combined, the manhole is placed in the 1400mm section. The calculated thickness of the cylinder in this section is small, and the cylinder can provide more additional reinforcement, so the calculation is qualified.
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In the 1600 long section, the calculated thickness of the cylinder is large and the additional reinforcement provided by the cylinder is small, so the calculation is unqualified.

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For example:
The dn3000 cylinder is made of 304 material at room temperature. The 1400 section is 7.58 thick and the 1600 section is 7.92 thick.
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Remedial measures

There are many devices with this problem. After changing to the actual location, if they are not qualified, they are usually solved by some remedial measures.
The reinforcing ring is thickened and widened.
Whether the position of the reinforcing ring can be adjusted appropriately, or whether a reinforcing ring can be added.
Try not to thicken as a whole due to unqualified reinforcement.

Summary

In the calculation of SW6, we often combine the nozzles, such as the inlet and outlet of tower equipment or heat exchanger. Because the external pressure calculation of SW6 uses the maximum length, as long as we ensure that the spacing between reinforcing rings is less than the calculation length of the maximum external pressure, this problem will not occur.
Pvelite is based on the actual position, and each tube section is calculated separately. Therefore, after the nozzle is combined, various problems may occur, especially after the reinforcing ring moves, it may be found that the calculation passing by the edge is not qualified.
So if we have to merge, we should merge to a conservative position.

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