PSI - Issue 46

Seong-woo Woo et al. / Procedia Structural Integrity 46 (2023) 169–174 Seong-woo Woo et al. / Structural Integrity Procedia 00 (2021) 000–000

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In the field, the evaporator tubes in a refrigerator were undergoing pitting and the refrigerant was leaking out of the tubes. As a result, refrigerators returned from the marketplace had no cooling so that consumers had to exchange their refrigerators. Field data demonstrated that the problem-atic products subjected to the repetitive loads might have had design flaws. The particular opera-tion states of the refrigerators by customers in the marketplace were unspecified. By a SEM with EDX spectrum, we discovered a chlorine concentration in the pitted surface that was measured as 14 PPM by Ion Liquid Chromatography (ILC) (Figure 2). Based on the anticipated customer operation states in the marketplace, we realized that the evaporator tubing in a cooling enclosure were subjected to repeated thermal duty loads due to usual refrigerator on/off functioning that will satisfy the thermal load. At right places the troublesome cooling enclosure had crucial design defects. Therefore, engineer had to reproduce the product failures by means of experiment and rectify them. To perform the parametric ALT, the cooling enclosure in a refrigerator was analyzed from the standpoint of the crevice corrosion. AF from Equation (2) may be restated as (4) From the experiment data of the worst occasion, the concentration of chlorine anticipated by the consumer in the operating cooling enclosure in a refrigerator was 0.33%. To perform accelerated testing, the concentration of chlorine in a cooling enclosure was almost increased to 3.69%. With a cumulative damage exponent,  , of 2, the whole AF was roughly 125. For the lifetime target – B1 life 10 years, the test cycles for 18 sample units computed from Equation (3) were 4,100 cycles if the shape parameter was presumed to have 2.0. 3. Results & Discussion In the first ALT, pipe tubes in a cooling enclosure are pitted at 1130 th cycle, 1160 th cycle, and 1680 th cycle. When the pitted pipes from the field and first ALT were disassembled, the pitting of the evaporator tubing in both the market products and the ALT test samples happened in the inlet/outlet of the evaporator tubing where the cotton adhesive tape with high concentration chlorine results in high corrosive stress. In the photographs, the form and place of the failure in the 1st ALT were alike to those discovered in the market. We thus knew that this methodology was well founded in identifying the design flaws accountable for field failures. (Fig. 3).                                                               1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 1 1 1 k T T E Cl Cl k T T E V V k T T E S S AF a a a n  

Fig. 3. Pitted evaporated tubes: (a) the field, (b) after first ALT.