Relationship between the Applied Torque and CCT to obtain the Same Corrosion Resistance for the Plate and Cylindrical Shape Stainless Steels

Many industries need the universal standard or technique to obtain the identical CCT regardless of specimen geometries. This study aimed to determine an appropriate applied torque to the cylindrical specimen defining the apparatus and the procedure to measure the temperature of initiating crevice corrosion in tubular shape products such as pipes, tubes and round rods etc; the test method also proved applicable to the plate type specimen. A series of experiments for CCT measurements with the plate type and cylindrical stainless steel specimens of various diameters with different microstructures (austenitic and duplex) and PRENs were conducted to determine the relationship among geometries on CCT. Thus, the apparatus that could measure the CCT of stainless steels with both plate and cylindrical geometries was newly designed. The use of the apparatus facilitated the same CCT value for both geometries only if the specimens were made of the same alloy. The applied torque can be calculated for various diameters of the cylindrical specimens using the following relation; Applied torque, Nm = -0.0012D(2) + 0.019D + 2.4463 (D; the diameter of cylindrical specimen, mm). However, upwards of 35 mm diameter cylindrical specimens require 1.58Nm, which is the same torque for the plate type specimen; in addition, this test method cannot be used for cylindrical specimens of less than 15 mm diameter.