The ASME code mainly specifies requirements for head shape deviation, including roundness, convex and concave shape deviation, but does not include specific requirements for head height.
The ASME specifications (such as ASME Section 1 and Section VII) provide detailed provisions for the shape deviation of the inner surface of formed heads. Specifically, there are clear control requirements for both external and internal deviations on the inner surface of the head. External deviation refers to the outward protrusion of the inner surface of the head relative to the ideal shape, while internal deviation refers to the inward depression of the inner surface of the head relative to the ideal shape.
In terms of measurement, the ASME code does not specify how to measure these deviations, but in the GB150-89 standard, it is recommended to use an inner template with a chord length of not less than 3D/4 to check the shape deviation of the inner surface of the head. However, this method has some limitations as it cannot fully contact the actual inner surface of the head, especially when the head has defects such as thinning, thickening, bubbling, and indentation
To address these issues, a gap template can be used to measure the internal and external deviations of the inner wall of the head.
In addition, the ASME code also includes provisions for the allowable roundness of the shell and head shape, head shape error, and alignment error of the welded joint section
These regulations aim to ensure that the size and shape of pressure vessels during manufacturing and installation meet design requirements, thereby ensuring their safety and reliability.