Long-term inside corrosion attack of an oil main operation

X-ray diffraction and metallographic analyses were applied when investigating the corrosion type and products of the cut-offs from an oil main with welded joints after its 33-year operation. Such a long-term effect of the transported medium and varying dynamic loading led to a considerable corrosion-mechanical damage to the inner surface of the pipe. The highest was the knife-line type of damage to the filler-parent boundaries of welded joints. The main corrosion products were Fe2O3 and Fe3O4 oxides that formed layers 300 to 350 pm thick. Beside the oxides, the deposits of hydrocarbon products (asphaltenes, resins, and paraffins), as well as calcium salts (CaCO3 and CaSO4), were present.