Aqueous sulfidic solutions which contain H₂S, or mixtures of H₂S and NH₃ are corrosive to carbon steel and other commonly used alloys particularly if the sulfidic solutions also contain chloride and cyanide ions. Titanium has been considered as a candidate construction material for services in petroleum refining and related processes, which involve handling aggressive aqueous sulfidic solutions. The corrosion and electrochemical behavior of titanium in aqueous sulfidic solutions was therefore investigated to provide answers regarding the corrosion and embrittlement behavior of titanium in these solutions. This paper summarizes the results of this study of the corrosion and electrochemical behavior, including galvanic effects, of titanium in aqueous acidic and alkaline sulfidic solutions. Variables investigated include the effect of solution pH, temperature and solution composition on the corrosion and electrochemical behavior of titanium. The effect of chloride and cyanide ions in aqueous sulfidic solutions on the corrosion behavior of titanium was also studied. Surfaces of titanium electrodes exposed to sulfidic solutions were also examined by reflection electron diffraction and the results of these tests are compared with thermodynamic predictions (Pourbaix diagrams).
An important factor which may also limit the utilization of titanium as a heat exchanger material is its ability under certain conditions to absorb hydrogen due to either superficial corrosion or galvanic coupling to more active materials. The absorbed hydrogen may lead to titanium hydride formation and embrittlement of titanium. This paper also discusses the results of an investigation of the effect of solution pH and composition, temperature, and impurity elements such as chlorides, cyanides, phosphates, etc. in solutions on the mechanism and rate of hydrogen absorption and formation of titanium hydride. In addition the effect of hydrogen and mechanical loading rate (strain-rate) on the ductility and embrittlement of titanium is also discussed.

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Corrosion behaviour of Cu-Sn-Zn-Pb alloy in air-saturated 3%NaCl aqueous solution was investigated by electrochemical measurement. Electron microprobe and X-ray diffraction analyser were used to study corrosion products. The free corrosion potential of the alloy was -0.48V (vs. SCE) at the initial stage of immersion tests; however it suddenly turned into more anodic potential, -0.20V, and didn't vary for more than 100 hours after that. In potentiostatic measurements, the needle-like crystal of Pb(OH)Cl was observed to be formed on the alloy electrode at the potential between -0.45V and -0.10V, and further, the protective film of CuCl-SnO mixture was formed on it at the higher potentials above -0.10V. From these results, it is considered that the dissolution of the alloy is inhibited because the surface of alloy is covered with the deposit of Pb(OH)Cl at the potential of -0.10V or below, and is covered with the film of CuCl and SnO at the higher potential above -0.10V.

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The influences of pH, sensitization treatment, carbon content and pre-cold working to the intergranular stress corrosion cracking (IG-SCC) susceptibility of Type 304 stainless steel were studied in boiling 20%NaCl+1%Na₂Cr₂O₇·2H₂O solution. Time to failure versus pH diagram of Type 304 stainless steel with and without sensitization treatment shows critical pH (1.8) at which the life is the shortest. The sensitization treatment at 650°C accelerates IG-SCC, but long time sensitization brings about the recovery of the IG-SCC susceptibility to the same as annealed state. In sensitized Type 304 stainless steel the transition of the cracking mode from transgranular to intergranular was often observed, however, the transition in the opposite direction was not observed. IG-SCC is obvious at higher stress level. On Type 304 grade stainless steel treated at 650°C for long time, intergranular corrosion occured in Huey test, however IG-SCC was not observed in this SCC test. Pre-cold work for stainless steel accelerates SCC at less than 10% reduction. The slightly cold rolled and sensitized specimens have the IG-SCC susceptibility, however, high cold working reduces the susceptibility to IG-SCC. Electrochemical experiments made it clear that natural potentials in steady-state of specimens during this SCC test corre-sponded to the active-passive transition region in boiling acidified 20%NaCl solution. It is concluded that IG-SCC of sensitized Type 304 stainless steel occurs when chromium carbides precipitate like network at the grain boundary.

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In order to study the characteristic of stress relaxation method (constant strain method) in stress corrosion cracking (SCC) tests, the changes of true stress and crack propagation rate during SCC were observed.
SCC of 18-8 stainless steels was tested both in H₂SO₄-NaCl solution at room temperature and in MgCl₂ solution at 423K. The reduction of residual area was closely related to the magnitude of stress relaxation during SCC. The true stress was gradually increased with crack propagation and saturated to a constant level. This stress level was increased with the initial applied stress. The crack propagation rate da/dt was linearly proportional to stress intensity factor K at the initial applied stresses below the proof stress. However, at 105% proof stress, the relationship between da/dt and K value was deviated from the above tendency.
Transgranular SCC was mainly observed by scanning electron microscope on fracture surfaces in both environments. But no dimple fracture surface was detected.

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The studies related to intergranular stress corrosion cracking of sensitized stainless steels in BWR environment have been reviewed with emphasis on the recently published results.
The effects of stress/strain factors, weld heat cycling, alloying elements and environmental factors on the stress corrosion cracking behavior in this system have been summarized.

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