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This paper studies the effect of expansion ratio on the corrosion rate of the expanded tubes exposed to sea water as well as the microstructure changes caused by the expansion of Cr-Mo steel tubes to large permanent deformations. 2.25 Cr-1.0 Mo steel (schedule 40 and schedule 80) tubes were subjected to various expansion ratios of 10%, 15%, 20%, and 25% by pushing conical mandrels through them using a piston. The microstructure was also studied to determine the effect of the expansion on the grain structure of the material. Microscopic examination of the expanded tubes revealed that grains elongate along the direction of the hoop stress and this elongation increases with an increase of expansion ratio. Moreover, it was found that corrosion rate and hardness increase with an increase in expansion ratio.

This work investigates the relative aggressiveness of nitrate solutions at different pH values on mild steel towards stress corrosion cracking (SCC) and general corrosion. Electrochemical behavior and stress corrosion cracking sus-ceptibility measurements were carried out in 52 Wt% ammonium nitrate solutions at 368° K and various pH values ranging from 0.77 to 9.64. Constant load stress corrosion test at 90% yield stress was conducted. Tested specimens were prepared and examined using the scanning electron microscope (SEM). The potentiodynamic polarization curves for different pH values again emphasized the validity of the gravimetric measurements and hence the mechanism of cracking was attributed to the stress that assisted the dissolution process

The effect of varying the temperature and the concentration of ammonium nitrate solution on the stress corrosion cracking (SCC) susceptibility of mild steel is studied. An increase in the temperature causes a decrease in the stress corrosion life. It appears that the susceptibility in the range 368 K to 380 K was greater than at other temperatures. Near the boiling point corrosion and stress corrosion occurs, at the boiling point, the cracking was associated with a high rate of general corrosion. Microscopic examination after stress corrosion testing in 10Wt%, 20Wt%, and 52Wt% NH4NO3 solution revealed that in all cases there was severe intergranular attack, especially at the high concentration