The nozzle of pvelite will cause great disaster after combined calculation

A long time ago, the company received a Japanese project. The equipment was designed according to ASME. Because the company had only one point, I was responsible for the calculation of all equipment for efficiency.
After the calculation, the equipment thickness shall be calculated, and the dimensions shall be marked and written to the designer.
The equipment in the project are some horizontal stainless steel tanks, the internal pressure is not high, and the negative pressure is full vacuum, which is basically 6mm – 8mm. By selecting the appropriate stiffening ring, the wall thickness and reinforcement are controlled to be the most economical.

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 shall be sent to the owner for approval after verification.
Many friends can understand that for the sake of project progress, many projects of manufacturing units are synchronized with design, procurement and construction. They will not purchase materials until the design is completely completed, especially the main materials – cylinder and head. The cycle is relatively long, so we should go first.
Therefore, while sending to the owner, the manufacturing process makes the main materials of the drawing as the first parts and orders first. Although there are appropriate risks, generally speaking, there will be no problem in the calculation of the main materials. Generally speaking, the problem is not big.

Here comes the problem

Two weeks later, the owner’s approval comments on the drawing calculation returned. There is one article in the calculation sheet:
Nozzles shall 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, it is found that two identical manholes, one can pass the calculation and the other is unqualified.
I was so scared that I was in a cold sweat. The plate has been ordered. The thickness of 304 materials of this equipment is 7.9MM. The actually purchased 8mm has been used to the maximum. If the cylinder is to be thickened, it will cause great losses.

Reason

After checking the calculation sheet, it turned out that due to structural reasons, the reinforcing ring was placed in the equipment center at first, and then there was a connecting pipe in the center, so for the 3M long cylinder, the reinforcing ring was placed 1400mm away from the left end weld.

When connecting pipes are combined, the manholes are 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 cylinder can provide less additional reinforcement, so the calculation is unqualified.

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For example:
The cylinder of DN3000, with one section of 1400 and one section of 1600, is made of 304 material at normal temperature. The 1400 section needs to be 7.58 thick and the 1600 section needs to be 7.92 thick.

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Remedial measures

There are many equipment with this problem. After changing to the actual position, if it is unqualified, it is generally solved through some remedial measures:

  1. The reinforcing ring is thickened and widened.
  2. Whether the position of the stiffening ring can be adjusted appropriately, or whether a stiffening ring can be added.

Try not to thicken the whole because the reinforcement is unqualified.

Summary

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

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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