There are different definitions and testing methods of ring stiffness in the world, and the physical meaning represented by ring stiffness is also different.

International upper ring stiffness standards mainly include:

German standard (DIN), international standard (ISO) and American standard (ASTM). Different from the German standard DIN 1696 1, the national standard ring stiffness refers to the European standard prEN 13476, and the calculation and design methods of ring stiffness in these two standards are based on ISO standards. Therefore, when determining the ring stiffness in pipe selection, the design standard of ring stiffness must be clear.

The rigidity specifications of carat collar are as follows:

Hardness of carat collar: SN8, SN 10, SN 12.5, SN 16.

The maximum stiffness of the carat collar of Dudley pipeline industry can reach 20KN/m2, and the coverage depth can reach 20m.