[en] Stability is dealt with, in accordance with the regulations and specifications, as the deformation of a cylinder under external hydrostatic pressure. The inner rings/tubes can, in fact, become instable. However, the load capacity depends on the size of the disturbance which in real components always exists between inner and outer walls. With real disturbances, the limit load is most always determined by yielding point and stress at failure; it is within the stable range of equilibrium. With loads in the plastic range of the material, the critical load can be determined taking into account a plastic joint, and subsequently compared with the load resulting from the stress computational method developed by Cozzone. In this calculation, a non-linear stress distribution accross the cross section is assumed. (orig./HP)