Method of estimating the diameter of a weld

An estimation method of a diameter (D) of a weld zone (9) having a center (C), said method comprising: - a positioning step (100) of an ultrasonic sensor facing said link, said sensor having at least one web (1) positioned at a distance (H1) of said center (C); - an identification step (200) of a first intersection (la) between said bar (1) and said welding zone (9) and a second intersection (Ib) between said bar (1) and said area of welding (9) respectively; - a step of calculating (300) a first value (D1) calculated from said diameter (D).