There are sufficiently long periods during the operation of steel structures, for which the structures do not experience the effects of external static and / or dynamic loads, except for their own gravity. A decrease in the level of the structure stress-strain state will promote relaxation processes in the substructure of the structural material. Сhanges in the substructure of 09G2S pipe steel were studied using laboratory samples. The samples were subjected to cyclic deformation in 2009 and then laid out for long-term storage. Multiple X-ray photographs of long time placed samples indicate a significant relaxation of stresses with a prolonged absence of a force field affecting the structural steel substructure. It was revealed that the experimentally determined values by the method of full width at half-maximum broadening of the diffraction lines profiles, measured in 2009 immediately after cyclic deformation of three groups of laboratory samples of low-alloy pipe steel at three different cycle stresses amplitude close to yielding, significantly decrease after holding for a long storage time in an unstressed state. It has been shown that the long-term storage of samples subjected to cyclic loading with the cycle stresses amplitude not exceeding the yield strength of structural pipe steel promotes the stress-strain state relaxation.