180 L. Liu et al. Normally a characteristic element has different impact on the reliability. The weight of the impact on the size is ω1, ω2, . . . , ωm. Then when the importance of various factors is considered, the measure of similarity between both is: k = m )R=1 ωR(μA1 (μR) ∪μA1 (μR)) m )R=1 ωR(μA2 (μR) ∪μA2 (μR)) (18.2) Obviously, when feature weight is not taken into consideration or the importance of attribute is identical, Eq. (18.2) translates into Eq. (18.1), which also means Eq. (18.1) is peculiar case of Eq. (18.2). 18.3 Reliability Lifetime Prediction for Plate Heat Exchanger Taking plate heat exchanger [15, 16] for instance, reliability prediction technology based on similar products is proposed. By comparing plate materials, plate structures, ocean water flow rate, heat transfer temperature, sealing rubber and so on, conversion factor can be got. With application data of history products and the calculated conversion factor, this paper transfers application data of history products into outfield experimental data of this product to evaluate its life. 18.3.1 Analysis on Similar Factors of Plate Heat Exchanger The cooler has high reliability when equipped in ships. As it is the first time that the cooler is equipped in certain naval vessel, before conducting reliability test, the data from civilian can be only used as references, and based on similarity analysis, its reliable life is analyzed and evaluated after calculating its life index. In the view of working mechanism similarity and structure similarity, both of heat exchangers adopt plate structure, so they share the same working mechanism; they are both designed in the standard of “plate heat exchanger” BN/T 47004-2009, and they both meet the requirement. According to the analysis on the similarity of structure and appearance, the compared sample exchange more heat and has a lager mass; however, the surface area, punching, groove and wave shape are different. Judged from performance index, the two products are obviously different in lube, water flow, temperature difference between import and export, quantity of heat exchanged and so on. The comparing product works in a more severe circumstance. 18.3.2 Usual Failure Mode and Sensitive Stresses on Plate Heat Exchanger Failure as leakage, fouling blocking stress corrosion damage and so on may come up to plate heat exchanger when it is designed or produced improperly, or the sealing structure is not reasonable, or the operation of installation and compaction is not proper, or the operating conditions of hot and cold media (pressure, temperature, velocity of flow and component) does not meet the requirements, or inspection, repair, maintenance are not timely. There are two main failure modes, i.e. deformation failure and corrosion failure. The main influencing factors for the deformation failure are the thickness of the plate and the fluid medium. Corrosion on plate heat exchanger occurs mainly on the cold side of the plate. Current velocity of the cold side has important influence on the corrosion rate. From the analysis above, the main sensitive stresses of plate heat exchanger are scouring water and heat transfer of cold side.
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