Revisiting Stress Corrosion Cracking of Steel in Caustic Solutions for Developing Cracking Susceptibility Diagrams for Improved Applicability

Distinct Advantages of Circumferential Notch Tensile (CNT) Testing in the Determination of a Threshold for Stress Corrosion Cracking (KISCC)

“…For example, for extracting alumina from ore (bauxite), aggressive caustic solutions are extensively used at high temperatures and pressures in digesters, decomposer and precipitator in the Bayer process. Temperature and composition of caustic solutions vary vastly across these pieces of equipment in a given plant as well as across industry [ 34 , 35 , 36 , 37 , 38 ]. It is crucial to have plant-relevant data on the thresholds of caustic concentration and temperatures for causing caustic cracking to steels, since reaction vessels and pipes are most commonly constructed from steels [ 17 , 18 , 19 , 20 , 21 , 22 ].…”

“…It is crucial to have plant-relevant data on the thresholds of caustic concentration and temperatures for causing caustic cracking to steels, since reaction vessels and pipes are most commonly constructed from steels [ 17 , 18 , 19 , 20 , 21 , 22 ]. On the basis of laboratory and industrial tests for up to 62 days at different caustic concentrations and temperatures, caustic cracking susceptibility (CS) diagrams (e.g., Figure 12 a [ 34 ]) have been developed. Such diagrams are used for the design and operation of alumina processing plants.…”

“…For example, the CS diagram suggests that steels in 15–40 wt% NaOH is most likely to suffer SCC at temperatures >95 °C, but cracking may or may not take place at temperatures <80 °C. The upper hatched area was constructed upon laboratory tests, whereas the field data were the basis for the construction of the lower curve [ 34 , 35 ].…”

“… Smooth samples of steel were used for developing the diagram [ 35 , 36 , 37 ], whereas the fabricated components often have sharp notches such as machining burs and other stress raisers such as surface defects. Therefore, it is prudent to investigate the validity of the caustic susceptibility diagram by testing notched and pre-cracked specimens [ 34 , 38 ]. …”

“… ( a ) CS diagram in a plain caustic solution superimposed with some data generated using CNT testing. CNT data: the stars represent the region of definite cracking, the rectangles represent the region of likely cracking, and the ellipses represent the region of definite absence of cracking [ 34 ]. ( b ) CS diagram in Bayer solutions, generated using CNT specimens showing caustic cracking susceptibility regions.…”