Characteristics of hydrogen-related failure are reviewed from mostly experimentally observed features. Comparison with the failure under normal atmospheres is made so as to extract the way by which hydrogen plays a role in the fracture process. Fractographic features associated with plasticity and the promotion of the crack initiation and growth analyzed by means of an R-curve method are presented. Enhanced plastic instability is noted as a precursor of the failure. Effects of hydrogen on stress relaxation and creep are presented as the dislocation dynamics that operate on delayed fracture. Effects of environmental variation of applied stress and external hydrogen potential are also presented.
We have developed a new atmospheric corrosion test device that can control the deposition rate of sea salt particles. By using this device, certain amount of seasalt particles were attached on the low alloy steel and the progress of atmospheric corrosion was observed by both the super Kelvin force microscope and Kelvin force microscope under various relative humidity conditions. The results showed that thin liquid film was formed around the corrosion part when corrosion occurred at high relative humidity. After the specimen surface was covered with thin liquid film, Cl− ion can move to the corroding part to increase the corrosion rate.
The techniques have been developed on removal of copper ion in the absorption refrigerator. Results are summarized as follows ; (1) Concentrations and chemical forms on copper ion and oxides in refrigerant and LiBr solutions in operating refrigerators were analyzed to be base data for removal techniques. (2) Examining removal technique by electrochemical reducing process, it was clarified that copper ion was effectively reduced to metallic state at the cathode potentials between −1.0∼−0.6 V vs. SSE. (3) Trial device has been made for removal of copper ion by 2 electrodes system. In the field test, it was clarified that copper ions in both refrigerant and LiBr solution were well collected on the cathode electrode to the concentration levels below the target value of 1 mg dm−3. (4) A filter device combined with active metal electrodes has been developed for removal of copper ions. Applying the developed unit to laboratory and field tests, it was verified that copper ions in both refrigerant and LiBr solution were well captured to the concentration levels below the target value.
After long term usage, troubles have been experienced recently such as lowering operation efficiency by plugging of spray nozzles with corrosion products in absorption refrigerator. To solve these problems, removal techniques of plugging by chemical cleaning have been investigated. The following conclusions were obtained: (1) Chemical cleaning solution of HCl with L-ascorbic acid was developed well designed to have high removal performance on Fe oxide deposit without any damage on copper tubes. (2) Applying the developed chemical cleaning solution to operating absorption refrigerator, it was proved that the plugging of spray nozzle by oxides was removed giving good operation efficiencies up to 85% from lower lebels of 30 %. (3) It was also clarified that no damages were observed on copper tubes with the developed chemical cleaning solution.
On the brazing part of copper tube and U bend in the fan coil unit, the solder was not corroded, and the soft copper tube that touches the solder has been corroded one-sidedly. Natural electrode potential of the solder and natural electrode potential of copper were measured on an unused brazing part sample in the tap water. The potential of the solder was about 100 mV higher than the potential of copper. It is guessed that the cause of corrosion is a bimetallic corrosion of which the solder is cathode and copper is anode.