The present invention provides a method of testing a cryogenic metal tank before it is put into service, in which said method said tank (1) is filled with water and appropriate measurements are performed where necessary, the method being characterized in that the following steps are performed: filling said metal cryogenic tank (1) with sea water; and providing the bottom and side metal walls (2, 3) of said tank (1) that are constituted essentially by bare steel, with temporary cathodic protection by injecting an electric current into anodes disposed within said tank (1) once said anodes become immersed. Advantageously, a first anode array (5.sub.1) is placed in the immediate vicinity of the bottom of the tank using support means (5.sub.2), said support means (5.sub.2) and said first anode(s) (5.sub.1) preferably being removable. Said first anodes (5.sub.1) are preferably disposed around a circle (C.sub.1) concentric about the center of the surface of the bottom of the tank, and preferably the diameter of said circle (C.sub.1) is 40% to 75% the diameter of the bottom surface (2) of the tank.