Field experiment of stress corrosion cracking behavior of high strength pipeline steels in typical soil environments

• The SCC behavior and mechanism of four kinds of high strength pipeline steels in five soil environments have been investigated via one year field test.
• All steels are susceptive to SCC under various typical soil environments, which in acidic soil is more serious than those in other environments.
• The susceptibility to SCC under the five tested soil environments is generally proportional to steel strength but inversely proportional to environment pH value.

In this study, the corrosion behaviors of four pipeline steels, i.e., X70, X80, X100, and X120, in acidic soil (Yingtan and Xishuangbanna), alkaline soil (Korla and Dagang), and dry sandy soil (Lhasa) in China were investigated using U-bend samples and notch crevice specimens by exposure testing. The morphologies and compositions of the corrosion products were analyzed by digital photography, scanning electron microscopy, and X-ray diffraction. The results indicated that all the tested pipeline steels exhibited stress corrosion cracking (SCC) susceptibility in the abovementioned three typical soils. The SCC susceptibility increased as the strength of the pipeline steels increased and as the soil pH decreased. In acidic soil, no relationship existed between the locations of SCC crack initiation and pitting occurrences. In alkaline soil, SCC cracks were mainly initiated at the bottoms of pits.