Taking the design of surge shaft as an example, the whole process of vessel design is explained.

First of all, within the scope of pressure vessel specifications, according to the legally binding design technical agreement put forward by users and signed by both parties, the agreement can also be modified and improved with the consent of both parties, so as to achieve the optimization of product use.

According to the design technical agreement of surge shaft, we know that the maximum working pressure of the vessel is 1.4MPa, the working temperature is 200℃, the working medium is compressed air, the volume is 2m3, and the required service life is 10 year. These parameters are the design basis provided by users.

With these parameters, we can start designing.

First, the first step of design

Is to complete the technical characteristics table of the container. In addition to heat exchangers and tower vessels, the technical features of general vessels include

Container category

Design pressure

design temperature

D medium

Geometric volume

F corrosion margin

J welding coefficient

Materials of main pressure components, etc. Generally, it is not mandatory to write the material of the main pressure components on the drawings of our hospital.

I. Determining the category of containers

Chapter 1, Article 6 (p7) of the Regulation on Safety and Technical Supervision of Pressure Vessels (hereinafter referred to as "Capacity Regulation") issued by the State Bureau of Quality and Technical Supervision stipulates the classification of vessels, mainly based on the magnitude of working pressure (p75), the harmfulness of medium and the harmfulness of vessel damage (p75). In this case, the surge tank is at low pressure (

In addition, the specific classification of pressure vessels can be found in the training textbook P41-1.

What is a flammable medium? See p2 1-6.

See p3 1-7 for the classification of toxicity degree of medium.

See p3 1-9 for the classification of pressure vessels.

2. Determine the design pressure

We know that the maximum working pressure of a container is 1.4MPa, and the design pressure is generally 1.05 ~ 1. 10 times of the maximum working pressure.

Whether to take 1.05 or 1. 10 depends on the harmfulness of the medium and the safety device attached to the container.

If the medium is harmless or equipped with a safety valve, the lower limit can be 1.05, otherwise the upper limit can be 1. 10.

In this case, the medium is harmless compressed air, and there is a pressure relief device in the system pipeline, which meets the condition of taking the lower limit, so the design pressure is

Pc= 1.05x 1.4

= 1.47 MPa.

What is design pressure? Calculate the pressure? How to determine? See p 1 1 3- 1.

How to determine the design pressure in the design of liquefied petroleum gas storage tanks.

3. Determine the design temperature

Generally, it is obtained by considering the ambient temperature of the container on the basis of the working temperature provided by the user.

For example, if the working temperature of a container designed for North China Oilfield is 30℃, and the lowest ambient temperature can reach -20℃ without heat preservation in winter, the design temperature should be -20℃ according to the worst possible temperature of the container. Annex II (p77) of the capacity regulation provides some meteorological data for reference. In this case, the design temperature is 200℃.

Four. Determination of geometric volume

According to the actual volume after the structural design is completed.

Determination of corrosion allowance of verb (abbreviation of verb)

It is determined by the selected materials of pressure components, the corrosion rate of working medium on pressure components, the use environment of containers and the expected service life of users. In fact, the material of pressure parts should be selected first, and then the corrosion allowance should be determined.

Table 3-3(p23) in Chapter 3 of the Capacity Gauge and 3.5.5.2 Chapter (p5) of GB150 have made some provisions on the corrosion allowance of some common media. The corrosion rate of working medium on pressure components is mainly determined by measured data and experience, which is greatly influenced by the use environment and has many variables, so there is no ready-made data at present.

Generally, the corrosion allowance of containers without corrosive medium is 1 ~ 2mm, which can meet the requirements of service life. In this example, the corrosion allowance is 2mm.

In addition: What are the calculated thickness, design thickness, nominal thickness and effective thickness? What is the minimum thickness? How to determine? See p 12 3-5 3-6.

Determination of welding coefficient of intransitive verbs

The standard name of weld coefficient is weld coefficient, and its value and weld detection percentage are specified in 3.7 (p6) of GB 150.

The specific value can be selected according to 10 specified in Article 85 (p43) of the capacity gauge:

The weld coefficient is 1, that is, the welded joint shall be subjected to 100% nondestructive testing; Otherwise, the welding coefficient is generally 0.85.

In this example, the welding coefficient is 0.85.

Seven. Determination of materials of main compression components

On the premise of meeting the safety and use conditions, the determination of materials should also consider the manufacturability and economy.

There are strict regulations on the use of materials on page 8 of GB 150, so it is very necessary to master these regulations. Commonly used materials are Q235-B(Q235-C) 16MnR and 0Cr 18Ni9.

1.0Cr 18Ni9 is generally used in low-temperature containers below -20℃ and

Containers requiring clean media, such as cryogenic separators and Freon evaporators;

2. 16MnR is generally used for Q235-B containers with high safety requirements and large wall thickness, such as oil and natural gas.

3.Q235-B is the most widely used and economical, and its use conditions are specified in detail on page 9 of GB 150:

● Specified design pressure ≤1.6 MPa;

● The service temperature of the steel plate is 0℃ ~ 350℃;

● The shell thickness shall not be greater than 20mm, and it shall not be used in highly dangerous media.

As far as this example is concerned, its pressure, temperature and medium all meet the requirements of Q235-B, only the thickness is unknown. If it exceeds 20mm, only 16MnR can be used, so Q235-B is tentatively used in this example.

Of course, if we follow the following methods:

● The specified design pressure is ≤ 2.5 MPa;

● The service temperature of steel plate shall not exceed 0℃ ~ 400℃;

Low shell thickness shall not be greater than 30 mm, and shall not be used in highly dangerous media.

The main difference between Q235-B and Q235-C lies in the different impact test temperatures. The former is a V-shaped impact test at 20℃. The latter is a V-shaped impact test at 0℃

After completing the technical characteristics table, the next step is container calculation.

◆ Determine the container diameter.

When calculating, the diameter of the container must be determined first. Unless required by users, the aspect ratio is generally 2 ~ 5, and in many cases 2 ~ 3 is enough.

This example requires the geometric volume of the container to be 2m3.

We should set the diameter first, then calculate the height of the cylinder according to this diameter and volume, and check its length-diameter ratio. The set diameter shall conform to the specifications of the head.

We set it to 800mm, and check Appendix B of JB/T4746 "Steel Pressure Vessel Head", and know that the head volume of this specification is 0.0796 m3.

Then:

The height of the cylinder is 3664 mm,

The aspect ratio is 3664/800=4.58.

If you add the height of the head, you can see that the length-diameter ratio is too large and the diameter we set before is too small.

Setting the diameter as 1000mm, it is found that the head volume is 0. 1505 m3.

Get:

The cylinder height is 2 164 mm.

The aspect ratio is 2164/1000 = 2.16.

If it is ideal, we determine that the inner diameter of the surge shaft in this example is 1000mm and the cylinder height is 2200 mm.

According to formula 5- 1(p26) of GB 150, the thickness of the container can be calculated to be 8.30mm.. This thickness is the calculated thickness, and its nominal thickness is the sum of the calculated thickness and corrosion allowance, and then rounded to the commercial thickness of the steel plate. In this case, the corrosion allowance is 2mm, the sum of corrosion allowance and calculated thickness is 10.30mm, and the recent commercial thickness of steel plate is 12mm, so the container thickness is determined to be 12mm, which meets the requirement of Q235-B that the thickness should not exceed 20mm.

In addition, in this case, the economy will be much better if the corrosion allowance is1mm. You can think about why.

So far, we have got the shape of the container.

◆ The next step is to configure the flange and nozzle of each nozzle according to the user's requirements and the provisions of the capacity gauge.

The opening on the container shall comply with the provisions of Section 8.2 (p75) of GB 150, and reinforcement calculation is generally required. Unless the conditions in section 8.3 (p75) of GB 150 are met, reinforcement calculation is not required.

When selecting the connecting pipe, the conditions in section 8.3 of GB 150 should be met as far as possible, and its safety and economy are the best, so as to avoid adding reinforcing rings.

In this case, the required nozzle diameter is within the range of Section 8.3 of GB 150, so the seamless steel pipe with φ57x5 is selected for the nozzle of the air inlet and outlet, and the seamless steel pipe with φ25x3.5 is selected for the sewage outlet. The flange shall be 1.6MPa convex (RF) flat welded flange (PL) according to HG20592.

◆ Flange and its sealing surface type

The type of flange and its sealing surface are required in the design agreement.

1. The pressure level must be higher than the design pressure;

2. Its material is generally the same as that of a cylinder;

3. When determining the position of the nozzle on the shell, in the case of narrow space, the weld spacing should generally not be less than 50mm to avoid the overlap of the welding heat affected zone.

In this case, the air inlet and air outlet are selected at a distance of 300mm from the girth weld of the upper and lower heads. Because the working temperature of the surge tank in this example is 200℃, there must be an insulation layer in its working state. Considering the thickness of insulation layer and the need of bolt installation, the distance between flange sealing surface and cylinder surface is 150.

◆ Inspection hole

In addition to the nozzle required by users, article 45 (p26) of the capacity gauge also stipulates the setting of inspection holes.

The diameter of this example is 1000mm, and a manhole must be opened according to the regulations. Check the standard JB580-79 "Practical Manual for Pressure Vessels and Chemical Equipment" p6 14 ",and select a manhole with a pressure of 1.6MPa and a nominal diameter of 450. The sealing type is type A, and its nozzle is φ480x 10. Because the manhole opening is large, it must be reinforced with reinforcing rings. According to the standard JB/T4736 of the stiffening ring, the outer diameter of the stiffening ring is 760, and the thickness is generally equal to the thickness of the cylinder. Manholes should be based on the principle of convenient access and as close as possible to the lower head. In this example, the center of manhole is apart from the girth weld 500 of the lower head.

The support of general vertical vessels is JB/T4724 (page 599 of Practical Manual for Pressure Vessels and Chemical Equipment).

In addition: how to determine the grade of forgings? What brand should be used for carbon steel and low alloy steel forgings with nominal thickness greater than 300mm?

◆ Fill in the nozzle table.

◆ Compilation of technical requirements

1 This equipment shall be manufactured, tested and accepted according to GB 150- 1998 Steel Pressure Vessels, and shall be supervised by the Safety Technical Supervision Regulations for Pressure Vessels issued by the State Bureau of Quality and Technical Supervision.

2 Arc welding is adopted for welding, and the brand of covered electrode is J422.

3. Unless otherwise specified in the drawing, the welding shall be carried out in accordance with the provisions of HG20583: the type of Class A and Class B welded joints is DU3；; See the nozzle table for the types of welded joints between nozzle and cylinder and head; The fillet size of fillet weld is the thickness of thinner part; Flange welding shall conform to relevant flange standards.

4 X-ray flaw detection shall be carried out for Class A and Class B welded joints on containers, and the flaw detection length shall not be less than 20% of the length of each weld, and the result shall be regarded as meeting Class III specified in JB4730.

5 After the equipment is manufactured, a water pressure test shall be conducted with the test pressure of MPa.

6 Nozzle, bracket and nameplate frame shall be oriented according to this drawing.

7 After the equipment passes the inspection, two layers of iron red alkyd primer C06- 1 and one layer of gray alkyd enamel C04-42 shall be painted on the external surface.

8 After the equipment is inspected as qualified, clean the interior, and each nozzle is sealed with a blind plate.

The calculated thickness of 10 equipment cylinder is mm, and the calculated thickness of head is mm. ..

The recommended service life is 10 year.

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