Structural improvement and strength check of plug valves

The plug valve uses a plug body with a through hole as an opening and closing element, and a valve that opens and closes through the rotation of the plug body and the valve stem. The plug valve has a simple structure, rapid opening and closing, and low fluid resistance. In this paper, some improvements and strength calculations have been made on the problems that occur with the plug valves used in drilling.

The opening and closing member of the plug valve is a perforated cylindrical body that rotates about an axis perpendicular to the passage to achieve the purpose of opening and closing the passage. Plug valves are primarily used to open and close pipes and equipment media. The main advantages of the plug valve are: it is suitable for frequent operation, rapid opening and closing, and light weight. Fluid resistance is small. Simple structure, relatively small size, light weight, and easy maintenance. The sealing performance is not limited by the mounting direction, and the flow of the medium can be arbitrary. No vibration, low noise. However, the plug valve used in drilling is often not easy to open after closing. This article has carried out a series of discussions and improvements on this issue.

Plug valve structure improvements:

The method of opening the channel in the lower part of the valve body basically balances the pressure on both sides, so that the valve is easily opened and closed, and the problem of the original plug valve is solved.

The improved plug pressure is calculated as follows:

1 Shell reference stress calculation A, ball valve hole center section 3-3

a. Analysis of tensile stress concentration A. Ball valve section 3-3

a. Stretching 2. Designed by the pressure vessel design in Chapter 5 of the Chemical Equipment Design Manual, it was found that the maximum stress of the opening of the cylindrical shell occurs at the point where the radial hole edge is parallel to the tangential direction and the circumferential direction, and the stress concentration factor = 2.5, that is, the stress concentration factor when taken alone is 2.5.

Yielding occurs near the stress concentration point. But less than 2, it is stable.

b. Torsion From the stress analysis near the opening in the pressure vessel design in Chapter 5 of the Chemical Equipment Design Manual, it can be seen that the thin-walled cylindrical shell with small holes undergoes torsion, and the maximum tensile stress occurs at the edge of the hole and the axis Above, the stress concentration factor of the torsion-reduced cylindrical shell of the small hole is taken as 4.

No yield will occur.

c. Internal pressure p=105MPa The effect of the stress concentration factor A=3.03 is obtained from the “Stress Concentration Factor Manual” when a thick-walled cylinder with a small hole in the cylinder wall is subjected to internal pressure.

In the stress concentration point to yield, but stable.

B, 2-2 at the section of the snap ring a, tensile from the "stress concentration" in the book to find A = 2.8

The yield occurs near the point of stress concentration (where the fillet meets the inner wall). But stable.

b, reversed from the "stress concentration" in the book to find A = 1.8

No yield will occur.

c. Internal pressure p=105M Pa. According to "Chemical Vessel", the local stress calculation method for different wall thickness cylindrical butt joints, the maximum stress on the thin-walled side (for warp stress)

C. Taper valve hole cross-section 4-4 a. Stretching It is designed by the pressure vessel of Chapter 5 of “Chemical Equipment Design Manual”. It is found that the maximum stress of the opening of the cylindrical shell occurs in the radial section, and the stress concentration coefficient A=2. (5) The stress concentration factor when drawing alone is 2.5.

Yielding occurs near the stress concentration point. But stable?

b. Torsion According to the stress analysis near the opening in the pressure vessel design in Chapter 5 of the Chemical Equipment Design Manual, it can be seen that the stress concentration of the thin-walled cylindrical shell with a small hole and the torsion effect, the maximum tensile stress appears in the axis On the 45° section, the stress concentration factor of the cylindrical shell subjected to the torsion of the small hole is taken as 4.

No yield will occur.

Section 1-1

a、Stretching is designed by the pressure vessel of Chapter 5 of “Chemical Equipment Design Manual”. It is found that the maximum stress of the opening of the cylindrical shell occurs at the point where the radial hole edge is parallel to the tangential direction and the circumferential direction. The stress concentration coefficient is A=2.5. , that is, the stress concentration factor when taken alone is 2.5.

Yielding occurs near the stress concentration point. stable.

b. Torsion From the stress analysis near the opening in the pressure vessel design in Chapter 5 of the Chemical Equipment Design Manual, it can be seen that the thin-walled cylindrical shell with small holes undergoes torsion, and the maximum tensile stress occurs at the edge of the hole and the axis Above, the stress concentration factor of the torsion-reduced cylindrical shell of the small hole is taken as 4.

No yield will occur.

3,1 Internal pressure 105MPa The "Stress Concentration Factor Manual" finds that the thick-walled cylinder with small holes in the cylinder wall is subjected to internal pressure and the stress concentration factor A = 3.03 can be obtained.

4 Conclusions No yielding will occur.

From the above stress analysis, the following conclusions can be drawn:

4.1 Under the action of three kinds of given loads, the stress under the action of tensile load is the highest, and the safety factor is the minimum. Therefore, the strength condition under tensile load is the main contradiction.

4.2 Tension is calculated using a common plug valve material 40CrMnMo. The safety factor is 1.71>1.5, which can meet the strength requirements.

4.3 Under tension load, the stress concentration at the opening of the knob is larger, and the material yield limit is reached at the stress concentration point. According to the new strength criterion, the maximum stress concentration point is 935.75MPa<2MPa, which satisfies the stability conditions.

4.4 The reference stress and stress of the inner groove during drawing are also large, but it can meet the strength requirements. Care should be taken when designing to reduce the stress concentration here.

4.5 Under given torsional and internal pressure loads, the safety factors for all dangerous sections are very large, and their strength problems may not be considered.