When studying the crack resistance of elements of welded structures, the energy criterion of failure is often used. The energy criterion is successfully applied to cracks propagating without a break, but when a crack strains at an angle to its original direction, the application of this criterion is constrained by the absence of a sufficiently simple method for calculating the intensity of the released energy of elastic deformations. G.P. Cherepanov and other researchers propose to calculate it using the concept of the energy flux vector. The proposed assumption allows to correctly calculate the values of its projection, but in fact, after the «fracture» of the crack, the form of the stress field in the vicinity of the peak sharply changes, which is expressed in a change in the stress intensity factors. As a result, the conclusions obtained are in satisfactory agreement with experiment and other fracture criteria only at small values. The example in the article shows that the intensity of the released energy does not have a vector property. Therefore, in the general case, one cannot use the concept of the energy flux vector.