EVALUATION OF THE EFFECTS OF GRAIN SIZE AND PLASTIC DEFORMATION ON THE SCC SUSCEPTIBILITY OF AL-BRASS TUBE MATERIAL

摘要

The fabricability, good corrosion resistance and high thermal conductivity of aluminum brass (Al-brass) material has made it widely used in heat exchanging unit of industrial plant equipment and heating coil units of crude oil carrier vessels. A heating coil tube made of Al-brass material (C68700) was reported to be attacked by stress corrosion cracking (SCC), resulted in unexpected leakage at the U-bent section. To determine optimum condition of the materials having higher SCC resistance, effects of grain size and plastic work on the SCC susceptibility of Al-brass tube material was evaluated. From the view of its fabricators and users these issues are critical to avoid both the loss of work efficiency and its future SCC failure. SCC tests using pH 7.2 Mattson's solution revealed that the primary factor for SCC susceptibility of Al-brass material was not the grain size but the degree of residual stress after plastic work. Thus, the control of grain size is not necessary to improve the material's SCC resistance. In contrast, the stress relieving after plastic work was the critical parameters to be controlled in preventing the SCC damage of the highly deformed tubes.