Regarding the K1 value of elliptical heads under external pressure
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There is a discrepancy between GB150 and the corresponding explanations; for standard elliptical heads based on the inner diameter, the value of Do/2ho is not equal to 2. Which standard should be followed?
Based on GB150, the definitions in the standards do not have legal validity; they are provided only for reference
In GB/T150, the definitions of standard end caps for internal and external pressures are indeed different: the K value is determined based on the inner diameter for internal pressure, while it is determined based on the outer diameter for external pressure. In the manufacturing process of elliptical heads, two different standards are not used based on external or internal pressure. Instead, the small tube end cap is based on the outer diameter, while the large cylinder end cap is based on the inner diameter. When considering elastic instability, the standards are based on the inner diameter. In other words, the K value is determined using the outer diameter when calculating the external pressure; the standard head is merely a conceptual notion. It’s really hard to understand why redefining the standard head for applications under external pressure is necessary, as indicated in Table 5-2 of GB150.3. However, whether it is standard or not is a matter of definition; it’s more convenient to use standard end caps in accordance with GB/T25198