Help needed! How is the minimum thickness for head forming indicated on the design drawings calculated?
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Inner diameter Di=1800mm, calculated pressure is 0.3Mpa, design temperature is 165°C, corrosion allowance C2=3mm, specified negative deviation for the head is C1=0. The material selected is Q345R low-alloy steel. According to the SW6 calculation results, the calculated thickness of the head is δh = 1.7 mm. The nominal thickness δnh = 10 mm. And the minimum forming thickness indicated for the head in the drawings is exactly 10 mm. The question now is: 1. How is the minimum forming thickness indicated for the head in the drawings calculated? Is it the nominal thickness δnh=10mm mentioned in the SW6 calculation sheet? Is it related to calculating the thickness δh=1.7mm? I saw a statement saying that rounding should be done based on “calculated thickness δh + corrosion allowance C2”. In other words, 1.7 + 3 + the rounded value = 4.7 + the rounded value = the minimum formability thickness. But if the minimum forming thickness is 10 mm, isn’t this rounding amount a bit large? Will it cause waste of materials? Is this method correct? 2. What is the relationship between the actual forming thickness = (blank thickness δS – machining thinning amount C3) and the minimum forming thickness of 10 mm specified in the drawings? 3. What is the relationship between the 12 mm indicated on the drawing and the nominal thickness δnh=10 mm stated in the calculation sheet?
With a calculated thickness of 1.7 and corrosion loss of 3, a minimum thickness of 4.7 is sufficient to ensure compliance; the minimum thickness specified in the drawings is 10, which clearly meets the requirements. 12 represents the initial thickness of the material, and this thickness decreases during the head forming process – for specific details, refer to GBT25198-2010
Additionally, when considering this head, one cannot rely solely on calculations of its strength; the reinforcement required for the access holes also needs to be taken into account
A common approach seen nowadays is to use the value of “{calculated thickness δ, minimum thickness specified by standards} + corrosion allowance C2” as a basis, rounding it up; if this value meets the requirements, it is then used to determine the minimum forming thickness δmin. So shouldn’t the standard specify a minimum thickness of 3 mm plus a corrosion allowance of 3 mm, resulting in 6 mm as the minimum thickness to ensure safety, rather than 4.7 mm?
The typical minimum thickness after molding = nominal thickness – reduction due to head processing; C3 = 12 – 12*0.13 = 10.44. The amount of reduction resulting from head processing depends on the equipment available at the head processing factory, with 13% being only a recommended value.
This post was last edited by WallaceLee on 2020-12-7 at 10:23. According to the provisions of GB/T 25198-2011, the value of 10mm indicated on this drawing represents the minimum thickness required for design purposes, δmin, while 10.44 is the actual minimum thickness achieved during the forming of the head, δ’min. Does it mean that the actual forming thickness δ’min≧the designed required forming thickness δmin?
Calculate and compare the reinforcement at the openings in the end caps for nominal thicknesses of 6 mm and 12 mm respectively, to determine whether reinforcement rings are necessary at the openings when the thickness is less than 12 mm. Moreover, the cylinder thickness should be considered; it is of course good to keep it consistent.
Ah, why worry about this? Theoretically, what you said about 6mm is correct
Your cylinder is also 12 inches thick, right? When considering the thickness of a component, it’s not sufficient to focus only on the strength of that component alone; sometimes it’s necessary to take into account the entire equipment as a whole. Therefore, in most cases, there is a considerable margin for the effective thickness of the end cap
The minimum thickness of a sealed head after molding can be calculated using the wall thickness reduction rate recommended in the appendix of GB/T25198-2010. However, the degree of wall thickness reduction for sealed heads is related to the manufacturing process, and it varies from one company to another; therefore, the best approach is to have the sealed head supplier provide this information.