Papers by Keyword: Service Life

Abstract: Mortar finishing is frequently used to improve the carbonation service life of structural concrete. Moreover, carbonation is aggravated due to global warmings, such as the increase of CO₂ concentration and temperature. This study shows a probability-based approach for evaluating the carbonation service life of coated concrete considering global warming. First, a carbonation model is proposed for assessing the carbonation depth of concrete with mortar finishing. The effect of global warming on carbonation is considered in the carbonation model. Second, a probability-based method is employed to determine the carbonation service life considering the thickness and mixtures of mortar finishing and substrate concrete. Based on the statistical analysis of calculation results, we find that for a concrete structural with 50 years’ service life, 15% service life will be reduced due to global warming.

Abstract: It has been observed that critical failures and loss of function occur in a shorter period than specified service life during operation of polypropylene pipes in hot water systems. The paper analyzes the failure causes of polypropylene pipes in closed loop hot water systems, and provides recommendations for increasing their service life. It has been established that the primary factors responsible for ageing and failure of polypropylene pipes during operation are medium temperature, stress due to internal pressure, water composition. It has been observed that a combined influence of the above mentioned factors provides a synergistic effect. We developed the recommendations for increasing a pipe service life, including close monitoring and recording of energy carrier temperature and pressure; changes in specifications for propylene pipes, including the recommendation for using random propylene pipe grades with high thermal oxidation stability in hot water systems.

Abstract: An analytical review of the effect of high-temperature thermomechanical treatment on the structure and properties of steels as a possible effective method of strengthening the teeth of excavator buckets. It is shown that the application of this method can have a positive effect not only on the hardness, but also on the entire complex of their mechanical characteristics, such as plasticity, impact toughness and fatigue resistance. In relation to Hadfield steel as the most frequently used material of the bucket teeth, it is noted that with increasing deformation grade of billets from 1 to 5, tensile strength of steel increases from 570 to 1030 MPa, yield strength – from 480 to 790 MPa, relative elongation – from 14.3 to 17.9 %, relative contraction – from 17.2 to 20.1 %, impact strength KCU – from 1.51 to 2.14 MJ/m². This article presents the results of metallographic analysis and comparative tests for abrasive wear of Hadfield steel samples after typical heat treatment practiced at bucket teeth manufacturers and thermomechanical treatment. It is established that high-temperature plastic deformation of steel samples before quenching increases their wear resistance by 1.7 times. The authors attribute the detected increase in wear resistance to the formation of fine martensite in the surface layers of steel with a needle size of 3-10 nm, which increases its hardness by 47%. It is concluded that the presence of fine martensite in the structure of Hadfield steel can increase the service life of excavator bucket teeth made of this material. The results of this study are planned to be used in the development of an improved technological process for manufacturing bucket teeth of excavators.

Abstract: Mortar surface coating is widely used as a finishing material to extend the service life and improve chloride ingression resistance of marine concrete structures. This study proposes a model for estimating the service life of surface-coated marine concrete considering climate change. First, the increase of chloride diffusivity due to climate change is considered using Arrhenius’ law. A two-layered chloride ingress model is used to analyze chloride profile. The probability-based approach is used to find the service life of concrete structures. Second, parameter analysis is performed considering the effects of various factors on service life. The influences of thickness and chloride diffusivity of the coating and substrate concrete on service life are highlighted. The reduction of service life due to climate change is clarified based on the regression of results of parameter analysis. For marine concrete with 50 years’ service life, 6% service life reduction occurs because of climate change.

Abstract: Rolling bearings are among the most widely widespread components in the engineering industry. A critical issue is damage to functional surfaces of rolling bearings, which has arisen during the operation. An important area is the monitoring of production temperature and its impact on components. We undertook this study to damage of functional surfaces bearings. It was decided that the optimal procedure is comparing three samples, each with another type of damage. This procedure will aid determine the cause of damaged bearings. This work has shown the adverse effect of residual austenite and residual stresses caused by the production process on the dimensional stability of the bearing components.

Abstract: In this paper, ordinary Portland cement concrete (OPC) and high performance concrete (HPC) were used in the marine environment exposure experiments, Using the second Fick’s law, five parameter of life prediction model-binding ability, diffusion coefficient of free C1- time dependent parameters, chloride ion concentration of surface and degradation effect coefficients are confirmed. The service life of OPC and HPC in ocean conditions is calculated and compared using mathematic software in atmosphere region, underwater region and tidal zone.

Abstract: The article contains the findings on impact of zinc coating specifications on corrosion resistance and service life of steels of various chemical composition used often in modern industries. Characteristics such as type, class, chemical compound and thickness of zinc-based coatings are also addressed. Experiments were performed in which corrosion rate and useful life of zinc coatings in probable operating-like conditions — i.e., in environments of varying degrees of corrosive power (humid and high-chloride environments) were determined. It has been established which one of the environments is the most corrosive for steels depending on the zinc-based coatings’ specifications. Qualitative (visual) and quantitative (gravimetric) assessment of corrosion resistance and service life of chosen steels is presented. Optimal hot dip galvanized coating specifications were determined using statistical analysis.

Abstract: This paper presents an evaluation of the minimum dipper stick service life in the unsafe cross-section; it is based on statistical simulation known as Monte Carlo method. Source data on the bearing capacity parameters as well as on the values of stresses in the unsafe cross-section are presented as small samples. Statistical simulation is used to create a finite general population of data on machine parts my means of an intermediate subpopulation using order statistics distributions.

Abstract: The oil industry of Russia currently needs innovative development projects aimed at a radical improvement of the performance of material resources and a decrease of their consumption. One of the most promising trends in corrosion protection is the production and use of pipes made of layered composite materials. There are several principal ways of producing them by metal forming processes. The world practice shows that lining technology is reasonable for oil well tubing. Lining consists in simultaneous expansion of pipes made of dissimilar materials, which possess different properties. A pipe of the kind manages to combine high corrosion resistance and mechanical strength, and this makes its service life more than 4 times as high as that of pipes made by conventional methods. However, previous foreign experience of manufacturing and using these pipes prompts the necessity of improving some pipe-making processes. This paper discusses new engineering solutions in the production of lined pipes, as well as in situ testing results.

Abstract: The paper discusses the computational and experimental approach for determination of the PM gears service life concerning bending fatigue in a gear tooth root. A proposed computational model is based on the stress-life approach where the stress field in a gear tooth root is determined numerically using FEM. The experimental procedure was done on a custom made back-to-back gear testing rig. The comparison between computational and experimental results has shown that the proposed computational approach is appropriate calculation method for service life estimation of sintered gears regarding tooth root strength. Namely, it was shown that in the case of proper heat treatment of tested gears, the tooth breakage occurred inside the interval with 95 % probability of failure, which has been determined using proposed computational model.