The torispherical head processed in China are generally 10% of the standard torispherical head, and its curved surface is much smoother than that of the 2: 1 elliptical head.

　　It has the following advantages when used:

　　It is easier to process than elliptical head, with small processing volume, good forming quality and cheaper.

　　The blank material used is less than the elliptical head, which saves more raw material.

　　The disadvantage is that the force is not as good as the elliptical head. The same diameter, pressure, and material are about 1.54 times thicker than the elliptical head.

　　If the internal pressure of the device is relatively small, it is very economical to choose torispherical head head.

　　In GB150, in order to avoid the instability of internal pressure, the inner diameter of the head with a minimum thickness of 0.15% for a standard elliptical head is specified, and the minimum thickness for a 10% disc head is not less than 0.3%.

　　In ASME, in order to avoid the instability of internal pressure, the disc heads are classified.

　　ts is the thickness, and L means the equivalent inner radius of the spherical shell.

　　For the ratio of ts / L less than 0.002, it shall comply with the mandatory appendix 1-4 (f).

　　Appendix 1-4 (f) is not only to calculate the thickness of general elliptical head, torispherical head head and conical head. Moreover, it is also considered to avoid the occurrence of internal pressure instability or yield failure in the corner transition area of the elliptical head and the dish head, and calculate the maximum allowable internal pressure of the head.

　　First calculate the internal pressure Pe that may cause elastic instability and the internal pressure Py that may lead to yield. Then calculate the Pe / Py value to determine the internal pressure Pek value that is expected to cause the corner transition zone to fail. Maximum allowable internal pressure.

　　Therefore, in ASME, detailed calculation is used to ensure that the head will not be unstable.

　　The total stress near the corner transition area of the dish / ellipse head is very large, and the stress direction is reversed.

　　On the one hand, to avoid brittle failure due to high-strength materials, on the one hand, in manufacturing, shape deviation or local thinning defects, the instability load for high-strength materials may be greater than the internal pressure limit load, and the instability precedes the strength failure.

　　Therefore, ASME stipulates that for all torispherical head and elliptical heads with K> 1 (that is, relatively flat elliptical heads), the allowable stress needs to be reduced.

　　The national standard uses the minimum thickness to control the internal pressure instability of the convex head. ASME uses a more detailed calculation to control the internal pressure instability. If in the national standard, the large-diameter head needs to be particularly thick due to the minimum thickness, you can refer to ASME Or HG / T20582 algorithm, detailed calculation can save costs.

　　If disc heads of high-strength steel such as dual-phase steel and chromium-molybdenum steel are used in the national standard, it is necessary to pay attention to whether there may be internal pressure instability. It is best to reduce the allowable stress for calculation or replace it with an elliptical head.