Help! Should stress concentration be considered in the design of static pressure vessels?
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Hello, seniors! Recently, while designing a pressure vessel (DN2500X14X1000, Q345R, with upper and lower elliptical heads plus a straight cylinder, 100% RT, PWHT), it was necessary to create square holes in the cylinder and then add square patches (1800X1800X32). Some supervisors suggested that attention should be paid to the stress concentration at the four right angles where the square plates meet the cylinder welds. I’m completely confused. I understand that the square patch has become integrated with the cylinder after welding, so there are no more geometric discontinuities (I’m not sure whether the exposed part of the patch needs to be taken into consideration). Additionally, the equipment undergoes 100% RT + PWHT; it’s not a fatigue-prone device, so stress concentration should not be a concern. Question 1: When designing static pressure vessels (mainly for reinforcement), is it necessary to consider stress concentration? If considered, how should stress concentration be calculated? Question 2: Can square-hole patches be reinforced using the equal-area method? Thank you!
Question 1: In the design of static pressure vessels, stress concentration needs to be taken into account, as it can affect the safety performance of the equipment. Stress concentration is more pronounced in the presence of welds and joints. Regarding the stress concentration at the four right angles of the welds between the square plate and the cylinder, as you mentioned, finite element analysis can be used to carry out calculations in order to determine whether reinforcement or additional structural improvements are necessary. The stress concentration factor can be determined through finite element analysis; generally, when this factor is less than 3, it can be considered to have no impact on safety. Question 2: Square-hole patches can be designed for reinforcement using the equal-area method. The equal area method is a simple and practical reinforcement design technique. Its principle involves finding an area of equal size on the structure to be reinforced, removing all the material from that area, creating a new hole in its place, and then using the same material to reinforce that hole. This method ensures that the strength and stiffness of the reinforced structure are not reduced, while also avoiding an excessive increase in material and weight. .
Here’s a suggestion: change the reinforcement members used in the calculations to ordinary circular tubes, and add unpressured square tubes inside the cylinder.
It’s my fault for not explaining clearly; the reason for using square patches is that the diameter of the pipe is too large, and it’s not possible to add reinforcing rings. To reduce the wall thickness of the cylinder, square patches with local thickening (1800X1800X32) were used, and holes were then drilled in these square patches.
You yourself said it’s chaotic; upload the drawings
Is it confirmed to be a rectangular opening? Rectangular openings definitely have the problem of stress concentration
The second question: can square openings be reinforced with an equal area of reinforcement? No. Take a look at the scope of application for equal-area reinforcement
Does the poster mean using rectangular reinforcement plates? The square corners generally need to be rounded
It’s not a rectangular hole, but rather a rectangular plate patch, with a circular hole cut into that rectangular plate patch.