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Question raised

The calculation of opening reinforcement in pvelite can be input in the tower model, or a separate cylinder can be built, and then the opening reinforcement can be calculated (i.e. opening reinforcement of tower and opening reinforcement of container). What is the difference between the two?

The difference between the two is generally not considered in GB, but a very strange phenomenon occurs when pvelite calculates a model.

- 1. The positive pressure is input for the integral tower model and the positive pressure is input for the component model. The calculation results of opening reinforcement are the same for both.
- 2. The negative pressure is input into the integral tower model and the negative pressure is input into the component model. The calculation results of opening reinforcement are the same.
- 3. The integral tower model inputs positive / negative pressure, and the component model inputs positive / negative pressure. The calculation results of opening reinforcement are different.

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Causes of problems

Why is such a wonderful result? I carefully checked the calculations of the two:

When the positive / negative pressure is input as the component model, the calculation results are as follows:

When the positive / negative pressure is input as the integral tower model, the calculation results are as follows:

Why are AR and A1 different? The following formula can be found by querying the cylinder calculation of the overall model:

Therefore, the causes of the problems are as follows:

The cylinder thickness required for internal pressure in the part model is 5.18mm and the required area is 2548.167; In the overall model, due to the tower bending moment, the minimum thickness of the tower needs to be 19.5 * 0.43333 = 8.45mm. Therefore, the required area increases proportionally: 2548.167 * (8.45 / 5.18) = 4156.7mm2

The remaining thickness of part model shell is 19.5-5.18 = 14.32, and the area provided by the shell is 7044.06; The remaining thickness of the overall model shell is 19.5-8.45 = 11.05, and the remaining area provided by the shell = 7044.06 / 14.32 * 11.05 = 5435.53mm2

This is consistent with the data in the previous calculation sheet.

In other words, pvelite considers the influence of wind and seismic bending moment on opening reinforcement when positive and negative pressure act at the same time.

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Problem solving

However, why should the influence of wind and seismic bending moment on opening reinforcement be considered only when positive and negative pressures act at the same time? If it needs to be considered, it should also be considered when the internal and external pressure acts alone.

**Note**: negative pressure is input separately in the overall model: the axial stress ratio is 0.433. However, Na is not calculated for positive pressure reinforcement.

The positive pressure is input separately in the overall model: the axial stress ratio is 0.4215, but the positive pressure reinforcement does not calculate the bending moment of the tower.

With the help of engineer Zhao, the reason was found:

When considering external loads for nozzletr is checked or unchecked, the calculation results will be different when the positive and negative pressures act at the same time.

Consider External Loads for Nozzle Tr

Select to calculate the nozzle area of replacement requirements using the required thickness of the shell. This value, tr, is critical in the ASME code. The software determines the maximum thickness based on the highest stress ratio and uses that value if it governs over the required thickness based on internal or external pressure. There are cases where pressure requirements do not govern the value of Tr. This can occur when a nozzle is located near the bottom of a tall vertical vessel. If there is a high wind load or seismic load on the structure, bending stress can govern the required thickness of the shell section. If this is the case, then the value of tr (per UG-22 Div. 1) should be based on the controlling factor.

It is a conservative algorithm. If the influence of axial force on opening reinforcement is not considered, it can not be checked here.

However, when only internal pressure or external pressure is considered, whether this item is selected or not has no impact on the results. The software here still needs to be corrected.

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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