I am concerned about the difference between European Code (EN13445) and ASME VIII, when calculating Spherical heads. My results shows a difference from 2 mm (diameter = 4000 mm) to almost 5mm (diameter = 10000 mm) in the required thickness of the spherical head. My question is if anybody has experience designing with european code and what this difference implies? Is the European code safe comparing with ASME? Is ASME too conservative? In other parts of the vessels (cylinder, conical,etc) the differences are much lower.
I’m assuming that you are sing Div 1 of the ASME code and not Div 2.
For most materials, EN 13445 has a lower design margin on material physical properties than ASME Section VIII, Division 1. But there are also additional requirements (testing, fabrication tolerances (see Part IV of EN), and perhaps more engineering calcultions that need to be performed depending upon the application.
If all the rules of both Codes are followed, I would not consider one to be “safer” than another. Even though EN is relatively new as a code, older European national codes had similar thicknesses as EN.
The new Div 2 is closer to EN in terms of thickness and has more engineering, fabrication, etc requirements than Div. 1. I recently spoke with a member of the ASME Section VIII design committe and he told me that a Div 1 vessel and a Div 2 vessel are supposed to be “equally safe”. Thinner sections with the trade-offs listed above.
I don’t know why the differences between EN 13445 and Div 1 would be much lower in other parts of the vessel. The basic formulas (cylinder, cone) are essentially the same (hoop stress is hoop stress) with the major difference being the allowable stress value. Cone to cyliner junctions are also treated differently in EN (no stiffening rings for internal pressure).
It is really impossible for someone here to give you a definitive answer to your question without all information. I suggest that you contact someone who is has knowledge with the codes to review your work if you are not familar with one or the other of them to make sure you are covering not only the design but also the fabrication/testing requirements.
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