It is shown that the method of small stresses sigma similar to 0.1 sigma(y) action on the metal created by the authors allows studying plasticity changes caused by the hydrogen action with high accuracy. The effects of elastic hysteresis amplitude omega(h) reduction under the action of several (n) hydrogenation cycles on non-strained samples and a significant (2.5 times) increase of omega(h) value after several hydrogenation cycles on strained samples have been detected. The effect of omega(h)(n) -> const was also detected and on the basis of which it was concluded that the hydrogen harmful action was best observed during the first cycles of hydrogen action. It is shown that a giant increase of omega(h) over several months is a sign of unpredictable destruction of low carbon steel after hydrogen action. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.