Corrosion Degradation of Steel of an Elbow of Gas Pipeline with Large-Scale Delamination after Long-Term Operation

The electrochemical corrosion behavior of the low-carbon steel of an elbow of gas pipeline after long term operation with extensive hydrogen-induced delamination was investigated in 0.3% (wt.) NaCl and 8.55 mM NaHCO3 aqueous solutions. The degradation of the corrosion resistance of steel from the pipe elbow in both investigated corrosive environments was revealed. The pipe steel of the elbow (both from the compressed and tensioned sections) was characterized by lower corrosion resistance than the metal of the straight section of the pipe. It was shown that the degradation of corrosion resistance of the pipe-elbow steel correlated with the degradation of its mechanical properties. It was established that the characteristics of corrosion resistance of the degraded material (corrosion current density and polarization resistance) could be informative about changes in its state caused by long-term operation and could be used for the diagnostics of the degradation of mechanical properties of hydrogen-affected steels.