Fluid machinery and environmental equipment that handle high-speed corrosive fluids are subject to risk of deterioration due to chemical and mechanical actions of such fluids and may eventually undergo operation shutdown, fluid leakage and/or explosion due to the damage to the machine, leading to economic loss and safety and security hazard. Chemical and mechanical actions of the fluid may affect the material respectively (corrosion or erosion) or in combination (erosion-corrosion). This report will summarize the phenomena and mechanisms of corrosion, erosion and erosion-corrosion of the material from the view point of the flow effect of the fluid (liquid, gas and solid) handled, and describe instances of, and measures taken against, the erosion-corrosion and slurry-erosion of pumps and the erosion-corrosion of heat transfer pipes of fluidized bed incinerator.
The various kinds of corrosion damage exist at a chemical plant due to the number of different materials handled. Among all, the damage caused by the flow has been an issue for a long time, and yet its cause remains unresolved because of the complex operation conditions. As such, this damage has been categorized as a so-called erosion · corrosion, and a corrosion prevention has not been investigated. This paper gives examples of erosion corrosion problems that occurred at chemical plants, and analyzes the damage from a new perspective. Many of the results do not correspond with the initial assumptions. As for the damage resulting from the flow, it is important to evaluate the condition of the material surface and examine the operation conditions. Through these analyses, the paper reports how the damage caused by the flow-an inherent problem in chemical plants-is to be tackled.
Various types of erosion damage have been experienced in chemical industries. However, the environmental conditions in the field are too complicated and complex to correlate the degree and occurrence of erosion damage in actual equipments. Only the past experiences, trouble information from similar plants and continuous inspection at the portions of equipments where erosion is suspected are only information to control and prevent the erosion. In this report, some examples of erosion damages experienced in our plants are described. And non-destructive inspection techniques applied to those erosion damaged irregular area to measure wall losses quantitatively in the fields are shown. Because of the limited reliability of the estimation of quantitative erosion damage from environmental or operational conditions, accurate non-destructive inspection of wall thickness is very important to keep safety of equipments.
Water droplet impingement erosion has been a severe problem of low pressure steam turbine blade materials in energy generation system. In order to estimate life of the blade materials, it is essential to investigate the impingement factors such as diameter, frequency and velocity of droplets in erosion testing methods. We investigated droplet impingement factors under various test conditions using water-jet testing apparatus, and compared the water-jet method with the cavitation testing method which was conducted in this paper. As a result, it was found that the water-jet testing apparatus is suitable for estimating the erosion damage, because of its uniform impingement conditions. And converting damage depth rate into volume loss, it was confirmed that erosion damage caused by water droplet impingement is related to the impact energy of the droplets at the high velocity region of water droplets. On the basis of the results, we proposed basic equations for prediction of material damage caused by water droplet impingement.
It is necessary to evaluate material performance from erosion tests under known water impingement conditions, in order to derive effective equations for estimating and predicting damage and life span of practical materials which suffer from erosion caused by water droplet impingement. Using a water-jet testing apparatus, impingement conditions of water droplets were obtained with aluminum foils mounted on aluminum specimen surfaces under several operating conditions. Fundamental equations for estimating erosion damage to materials were proposed in the previous paper. In this paper, effects of impingement parameters such as velocity, frequency and diameter of water droplets on erosion behaviors were investigated with water droplet erosion tests for ordinary carbon steel, stainless steel and carbon tool steel as industrial materials. As a result, estimative equations of materials for erosion by water droplet impingement were precisely derived and validated from the test results. This paper introduced life predictions of industrial materials with the incubation period which is one of most important factors in the erosion behavior.