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                  tannin concentration of 1.0 g/dm . It has been found that the inhibitor blocks freshly
                  formed surfaces, inhibiting their anodic dissolution, at the stage of crack initiation

                  and inhibits hydrogenation at the stage of crack growth.

                         A method for predicting the effectiveness of inhibitory protection of ferritic-

                  pearlite steels of sucker rods against corrosion-fatigue failure in formation water has

                  been  developed.  The  method  is  based  on  the  established  correlation  between

                  electrochemical (amount of electricity spent for metal oxidation of freshly formed

                  surface  at  corrosion  potential)  and  corrosion-mechanical  (corrosion-fatigue  crack

                  initiation period) indicators.

                         The influence of operation conditions and hydrogenation on the anisotropy of

                  characteristics  of  strength,  plasticity,  impact  toughness,  resistance  to  hydrogen

                  embrittlement  and  fracture  toughness  of  rolled  pipeline  steels  depending  on  the

                  orientation  of  the  plane  of  fracture  propagation  in  axial,  tangential  and  radial

                  directions have been assessed. It has been demonstrated that hydrogenation of long-

                  term  operated  rolled  ferritic-pearlitic  pipeline  steels  significantly  enhances  the

                  anisotropy  of  their  mechanical  properties,  especially  plasticity,  impact  toughness,

                  resistance  to  hydrogen  embrittlement  and  fracture  toughness,  due  to

                  microdelaminating  between  fibres  and  in  the  vicinity  of  non-metallic  inclusions

                  along rolling direction and fracture of membranes between them by transgranular

                  chipping.  It  has  been  established  that  the  tensile  deformation  energy  of  the

                  hydrogenated  specimen  with  a  crack  before  its  start  in  the  direction  between  the

                  fibres is 60 times less than across the fibres.

                         Scientific novelty of the obtained results.

                         It has been established that structural-free ferrite mostly dissolves at the initial

                  stage of corrosion of the ferritic-pearlitic 50Г and 32Г2 steels in 1% NaCl solution

                  with  pH  =  3.1  and  CO 2  bubbling  into  the  solution,  which  simulates  formation

                  waters;  the  fraction  of  structural-free  ferrite  in  the  steel  microstructure  is  the


                  dominant factor of corrosion intensification.
                         The influence of microstructure of ferritic-pearlitic steels of casing pipes with


                  different strength on resistance to hydrogen embrittlement has been defined: the 32Г2
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