The formula of the American Society for Testing and Materials F 1216-93 [ASTMF121693] for calculating the critical buckling pressure is the result of investigations of hose liners in steel pipes in which the diameters, the wall thicknesses and the modulus of elasticity were varied. The liners were loaded to failure and the experimental buckling pressures were compared with the critical buckling pressure of the free pipe according to Timoshenko (Formel 220.127.116.11.1.2.1) with an increase factor K (support factor). The calculating formula of the critical buckling pressure pcrit to [ASTMF121693] is:
For K the minimum value of K = 7 is recommended. The deformation factor fa corresponds to the value determined by Gaube according to (Formel 18.104.22.168.1.2.2).