This article reports on the failure analysis of the geothermal steam pipe. Macro and micro examination of failed pipelines was studied using optical and scanning electron microscopy. The energy-dispersive spectroscopy studied the elemental composition of the corroded surface. Further, the study measured the pipe thickness on the failed pipeline section. Visual examination showed a significant thinning of the outer section of the failed pipe to 3 mm from 12.7 mm of the original pipe. The chemical composition results show that the steel meets the minimum requirements for API 5L Grade B steels used in steam pipelines for geothermal power plants. The microstructural analysis of the investigated steel shows that the steel had pearlite and ferrite phases. The steel failure mechanism was due to erosion-corrosion, which caused localised wall thinning near the drain port and elbow section. The study recommends creep-resistant steel for the drain port and elbow for geothermal power plant application.

In this study, the influence of the volume fraction of the martensite phase as well as the size of the martensite particles on the mechanism of particle fracture in dual-phase steel were examined. A combined continuum/dislocation based approach was used in order to model the average stress in the martensite particles. It was found that the model predictions are in accordance with the experimental results. For the same volume fraction of the martensite particles, the model predicts an increase of the internal stress and the average stress in the martensite particles with increasing the particles size. Since the fracture strength of the martensite depends on its volume fraction, the particle size has no effect on the mechanism of particle fracture. Increasing the volume fraction of the martensite particles results in the enhancement of the internal stress in the martensite particles. However, it has a slight influence on the average stress in the particles. Nevertheless, because of decreasing the fracture strength of martensite with increasing its volume fraction, this parameter has a main role in the occurrence of the particle fracture mechanism.