In the first paper on the chloride-SCC of austenitic stainless steel SUS 304 under combined tensile and torsional loading, the authors had a conclusion that the SCC threshold stresses could be evaluated by the equivalent stress of total strain energy theory.
This second paper is concerning with the chloride-SCC of austenitic stainless steel SUS 304 under combined internal pressure and tensile loading where both the maximum and the minimum principle stresses are tensile.
Stress criteria for mechanical elastic failure and stress corrosion cracking, crack pattern and morphology under combined stress states were studied.
Test results obtained are summarized as follows;
1) A SCC test apparatus with the mechanism of inducing only a hoop stress by compressing soft rubber was newly developed, which made possible to produce any stress states in the first quadrant of rectangular principle stress coordinate.
2) Equivalent stress by Von-Mises shear strain energy theory becomes a stress criteria for mechanical elastic failure under wide combined stress states of -1≤n=σ₂/σ₁≤∞. Threshold equivalent stress of SUS 304 at 145°C is 15.2kg/mm₂.
3) Threshold stress of SCC under combined stress states of 0≤n≤∞ could be evaluated by the total strain energy theory with some modification. There exists some deviation of experimental data from the theory of failure due to the anisotropy of mechanical properties in the range of 1<n≤∞.
4) Fractographic examination showed that there existed some characteristic cracking mode such as extrusion like pattern under the stress states where the hoop stress is equal to or larger than the axial stress.

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The intergranular stress corrosion crack (IGSCC) propagation behavior was studied for sensitized stainless steels by means of the CBB test in high temperature, high purity water. A number of duplicated specimens were tested for the purpose of statistical analyses. Results are summarized as follows. (1) A number of cracks were generated on a furnace-sensitized specimen, and their depth distribution can be fitted to the normal probability distribution. (2) The maximum crack depth distribution for each duplicated specimen can also be fitted to the normal probability distribution, as well as to the doubly exponential (largest value) probability distribution. (3) There exists the critical crack depth of around 50μm for propagation. The crack starts steady propagation immediately after exceeding the critical crack depth. (4) The average crack velocity strongly depends upon the degree of sensitization of material, but not so upon the test temperature.

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Hydrogen absorption by titanium coupled with dissimilar metal such as mild steel, stainless steel and naval brass was investigated in deaerated 0.01%Na₂SO₄ solution at high temperature simulating the environment of shell side of brine heater in a desalting plant.
As a result, uncoupled titanium and titanium coupled with stainless steel and naval brass did not pick up hydrogen in the solution even at 150°C but it coupled with mild steel picked up hydrogen over 120°C. Corrosion rate of mild steel and hydrogen content in titanium increased with an increase of Ti/Fe area ratio. Moreover, Fe₃O₄ deposited on the lower part of titanium specimen and hydrogen content in titanium was much in the Fe₃O₄ deposited part.
Fe₃O₄ seems to be formed from Fe(OH)₂. It was clarified that corrosion potential of titanium shifted to less noble side in a high concentration Fe(OH)₂ solution. Therefore, it is considered that titanium absorbs hydrogen because hydrogen evolution reaction on titanium is accelerated by Fe(OH)₂.
Subsequently, an appropriate countermeasure against hydrogen absorption was investigated and hydrogen absorption could be prevented by thermally oxidation of titanium.

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The effect of heat treatments and minor elements (C, S, P, N) on caustic stress corrosion cracking of Type 304 stainless steel in boiling 34%NaOH solution at 393K was studied. The results obtained as follows:
(1) Susceptibility to IGSCC (intergranular stress corrosion cracking) in NaOH solution was increased with the intergranular precipitation of chromium carbides by the sensitizing heat treatments, but was not completely consistent with the susceptibility to IGC (intergranular corrosion) by Strauss test in H₂SO₄+CuSO₄ solution.
(2) SCC in NaOH solution took place in three potential ranges of about -100 to +150mV (vs SCE), -600 to -300mV and -1100 to -900mV. Transglanular crackingpredominan tly occurred in the first region and intergranular cracking occurred in the latter two regions. IGC occurred in the potential range of about -400 to 0mV. No IGC was observed at corrosion potential.
(3) Among minor elements carbon and sulfur had a detrimental effect on SCC, but no effect of phosphorus and nitrogen was almost observed on SCC in NaOH solution.

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Corrosion behavior of four materials (gray cast iron: FC20, low-chromium gray cast iron: ES51F, austenitic gray cast iron: A. S. T. M. A 436 type 2, mild steel: SS 41), which are frequently used for pumps, was investigated in flowing water (7 kinds of flow speed range from 0 to 15m/s) containing chloride ion (6 levels of concentration range from 25 to 30, 000ppm) at 30°C. Equicorrosion-rate charts were constructed in a similar way of drawing a map and were successful in indicating effects of flow speed and chloride ion concentration simultaneously. FC 20 and ES 51 F showed similar behavior and both had a peak of corrosion rate at the condition of approximately 580ppm Cl^- and 0.5m/s. By comparison of FC 20 with ES 51 F on the whole, ES 51 F was superior to FC 20. The behavior of SS 41 was dissimilar to FC 20 and ES 51 F. SS 41 revealed a peak of corrosion rate at the condition of approximately 5, 600ppm Cl^- and 5m/s, and its peak (over 1.4mm/year) was higher than that of FC 20. Corrosion rate of A 436 type 2 was 0.5mm/year even at the maximum and revealed no peaks in this test condition, and it was confirmed that this material has good durability for pumps.

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