Tube steel operation properties changes in oil production

Bending tests, metallographical tests and fractographic analysis were performed. The steel 20 degradation factor was set in operatingconditions; it can cause accidents together with the local corrosion.
Results
Combined impact of steel embrittlement and local corrosion may cause serious accidents, occurred in the pipelines steel.
Сonclusions
1. The microstructure of the tube steel 20 without having been in operation, and the tube after eight-year maintenance is a two-phase mixture of ferrite grains and pearlite stock. There is a diff ence in ferrite and pearlite grains size. The average size of grains is 10,0±1,0 um, and for steel after service life it is - 5,0±0,5 um.
2. The coefficient of the fractional change of the impact number during the temperature falling was selected as the quality factor of the metal embrittlement during the sour gas service.
3. The comparison of steel impact viscosity of the tube, not being in operation, and the tube after the sour gas service, showed traces of steelembrittlement during the operation. It resulted in the coefficient X increased by 25,3% (embrittlement rating).
4. The tube steel embrittlement during the operation was proved out by the results of the samples fracture surface fractographic analysis after the impact bending test.
5. Combined impact of steel embrittlement and local corrosion may cause serious accidents, occurred in the pipelines, pumping sour crude products of wells.