Experimental study on the compression mechanical behaviour of steel pipes with mechanically induced pitting corrosion

Pitting damage severely degrades the mechanical properties of the main force-bearing member of a circular tube; it can also change its failure mode. Offshore high-strength seamless steel pipes with steel grade X52Q certified by ABS were selected for a pressure test and research. The constraint conditions of one hinged end and one fixed end were adopted to investigate the effect of the bending moment of the nodes so that any section of the circular tube can be subjected to the superposition of axial force and bending moment. Pitting craters were generated using mechanical processing methods; the effect of pitting parameters such as diameter, depth, and distribution on the mechanical properties and failure modes of circular pipes was explored. Pitting corrosion damage caused local stress concentration and the local cross-section weakening of the tube. In addition to the decline of the bearing capacity under the action of axial compression load, the failure mode of the pitting corrosion damage tube also showed differences. Increased local damage caused by the increase in the diameter of the pitting corrosion was likely to cause plastic hinges on the pits of the tube, and this changed stress conditions, failure modes, and failure locations of the components. An increase in the depth of the pitting craters resulted in a significant drop in the overall load-bearing capacity caused by local buckling. The location of pitting corrosion had negligible effect on the mechanical performance of the tube; the end distribution was more unfavourable than the centre distribution. The stress–strain distribution characteristics of the pitting area of the specimen were considerably different, and the stress concentration on the inner side of the pitting corrosion were serious and uneven. The results of the experimental analysis and several numerical examples indicated that pitting corrosion causes the pressure-bearing circular pipes with lower strength buckling to more likely suffer from an instability failure.