Formerly first in the world calculated the correction to be applied to the large diameter pipes test pressure due to the back counter-pressure of the hydraulic test machines. I used equations provided by Von Mises (criterion of relative streng in ductile materials based on the maximum energy of distortion). My algorithm was the first in the world, used to calculate the test pressure pipe API X60 grade OD 30" pipeline intended to Michigan in 1974. This criterion was accepted by all testers for over 10 years, but in 1989 it was replaced in trhe API stds by a formula derived from the 'tau max' theory (that is maximum shear stress). This last method - good for lower diameter/thickness ratio - provides ​​discontinuous values with the diameter, and generally values much more favorable to manufacturers for greater diameters.. In case of large diameter pipes, when the shear stress is negligible because higher ratio diameter/thickness. instead my formula is much better and realistic.

My method, best for large diameter pipes, it is with high ratio between diameter and thickness, gives instead continuous results - obviously..
In this occasion (and also in other similar situations) I was struck by the low mind elasticity and insulting attitude of sufficiency shown by the API Technician who in 1988 couldn't understand why I had reduced my 1974 formula to a step by step algorithm.
Note:the management called me to explain formulas and algorithm to this fellow, when I was then working from years in the hot strip mills. In fact, because in '74 we did not have PCs, I made a simple step table - different for the oldest and newer pipe mill to facilitate other employees who had to calculate the testing pressure manually .