Takeover opening reinforcement
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I have a question: what is the difference between equal-area reinforcement and pressure-area reinforcement? I’ve read many papers on this topic but still find it confusing. For equal-area reinforcement, the forms of reinforcement include reinforcement rings and nozzle reinforcements; so what about pressure-area reinforcement – are the reinforcement forms the same? Is it just that the range of reinforcement is different? Is that the correct way to understand it? Seeking help from experts for a solution
It’s a document I prepared earlier; feel free to take a look, haha. 2.1 Equal-area method: The equal-area method suggests that for the load-bearing area of a shell that is reduced due to openings, reinforcement material should be used to compensate for that loss in area around the openings. This method is based on the stress concentration at the edges of holes in a biaxially stretched infinite plate with holes, takes into account only the tensile film stress present in the shell, and uses the primary stress strength of the reinforced shell as the design criterion, making it safe and reliable for small-diameter openings. However, this method does not take into account the effect of stress concentration at the openings, nor the effect of changes in the container diameter. Therefore, in order to reduce the discrepancy between the actual stress concentration factor and the results of theoretical analysis, there are certain restrictions on the size and shape of openings for the use of the equal area method. For example, GB150 stipulates that when the diameter of the cylinder Di is ≥ 1500 mm, the maximum diameter of the opening dop must be ≤ Di/3, with dop also being ≤ 1000 mm. 2.2 Pressure Area Method The pressure area method is a technique based on the force balance between the compressed area and the load-bearing cross-section; in other words, the total force generated by the pressure on the compressed area is balanced by the load-bearing capacity of the areas of the shell, fittings, and reinforcing materials within the effective reinforcement range. However, the pressure area method takes into account only the static requirements of the overall and local membrane stresses at the edge of the opening, without considering the effect of bending stress; essentially, it is the same as the equal area method. However, the reinforcement results achieved by the two methods differ, mainly because the two approaches consider different effective reinforcement ranges for the cylinder. For the equal-area method, the range of stress concentration reduction at the hole edge depends entirely on the hole diameter, and is independent of the cylinder diameter. In the pressure area method, the attenuation region based on the boundary effect of the cylindrical shell depends only on the inner diameter of the cylinder, and not on the diameter of the opening. This results in a relatively small reinforcement area according to the pressure area method when the opening diameter is large, giving it the characteristic of dense reinforcement; it can effectively reduce stress concentration at the opening connection areas, thereby making the intersecting shell sections safer. This is also the main reason why the pressure area method can be applied to large openings. HG/T 20582-2011 \"Specifications for Strength Calculation of Steel Chemical Vessels\" adopts this method for the reinforcement calculation of large openings. HG/T 20582 specifies that in cases where no reinforcement of the nozzles is provided or is not taken into account, and only thickening of the shell is used for reinforcement, the requirement for the opening diameter d relative to the inner diameter Di of the cylinder is that d/Di ≤ 0.5.
I agree with you; it’s explained in great detail.
If calculating standard national equipment, it is not recommended to use the pressure-area method. It is recommended to use the equal-area reinforcement method or analytical method for design calculations. Because the pressure area method has defects, accidents may occur even when the calculations show it is acceptable.
That’s why the pressure area method has never been included in GB.
Calculated using the pressure-area method, have any accidents actually occurred?
It is unclear whether any accidents have occurred; what is clear is that the calculation principle behind the pressure area method for determining reinforcement required for openings has inherent flaws. If there is really no other way to perform the calculation and the pressure-area method must be used, it is recommended to apply a larger margin of safety. Those who have used this method in the past certainly used a substantial margin of safety, which improved reliability.
Do all openings need reinforcement?
No, there is also a range for this; you can take a look at GB150.3