Calculation of the shell thickness at openings within 80% of the diameter at the center of the elliptical head of an internal pressure vessel
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The last edit to this post was made by Dongfang1979 on 2020-5-13 at 18:49. For clause 6.3.3.2(c) of GB/T 150.3-2011, the thickness δ of the shell at a location where an opening is situated within 80% of the diameter from the center of the elliptical head of a vessel under internal pressure is calculated using equation (6-2). The value of K1 in this equation is taken from Table 5-2 in section 5.3.3 “Elliptical heads under external pressure”. There are currently two questions: 1. In equation (6-2), the coefficient K1 is used, and it is determined by the ratio of the major to minor axes of the ellipse, as can be found in Table 5-2. Coefficient K1 is the coefficient used for calculating the thickness of an elliptical head under external pressure, whereas what is calculated in 6.3.3.2 c) is the thickness required for reinforcing openings in an elliptical head of a vessel under internal pressure – is there any contradiction between the two? What is the basis for this calculation? 2. As can be seen in Table 5-2, K1 is determined using the formula 【Outer diameter of the head / 2 × (Depth of the head’s curved surface + Thickness of the head)】. Note 2 states that for standard elliptical heads, a value of 0.9 should be used; in this case, the value calculated using the formula in the table is 2.0. However, for standard elliptical heads, the value of 【Inner diameter of the head / 2 × Depth of the head’s curved surface】 is also 2.0. Therefore, it’s clear that 【Outer diameter of the head / 2 × (Depth of the head’s curved surface + Thickness of the head)】 cannot equal 2.0. Is there any problem with this? Additionally, the K1 value in SW6 is determined based on 【inner diameter of the head / 2 × depth of the head’s curved surface】, rather than based on 【outer diameter of the head / 2 × (depth of the head’s curved surface + thickness of the head)].
This post was last edited by zjq1962 on 2020-5-13 at 20:50. The original poster does indeed pay close attention to the standards. In ASME Section VIII-1, there are two tables (although the spherical coefficient values in both tables are exactly the same); Table UG-33.1 is used for calculations related to external pressure, while Table UG-37 is used for reinforcement calculations. The first table provides the spherical radius coefficient K0 for elliptical heads under external pressure, based on the ratio Do/2ho, whereas the second table gives the spherical radius coefficient K1 based on the ratio Di/2hi.
Thank you for your reply; it will be clear once I look at ASME. It seems that there is an issue with the calculation in GB/T 150-2011; if it is not a standard elliptical head, selecting the K1 value based on Do/2ho results in an overly thin shell thickness at the opening. Note 2 in Table 5-2 and Do/2ho=2 in the table are also contradictory.