PSI - Issue 47

Fatima Gugouch et al. / Procedia Structural Integrity 47 (2023) 952–958 Fatima Gugouch/ Structural Integrity Procedia 00 (2019) 000–000

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3. CPVC Bathtub Curve To plot the curve of reliability Fig. 5, we based on the generality that reliability varies in opposite direction with the damage. A method for evaluating and predicting the lifetime of the studied specimens is based on the drawing of the bathtub curve from the damage and reliability curves. It is established according to the stages of theoretical damage, as shown in Fig. 5.

Fig. 5. Damage and reliability curves as a function of the fraction of life.

The first stage determined in Fig. 5 is an infant phase revealing premature damage, will be considered below the level of 24% of the degradation. The second, when maintenance personnel must make the decision on preventive maintenance, which corresponds to the useful life, takes place between 13% and 74% of the life fraction. Beyond that, the third stage corresponding to the acceleration of the damage, wear, is perceptible. From this moment, the bathtub curves will take another shape as shown in the figure above. 4. Analyze Based on MTBF and MTTR The MTBF has a decreasing form represented by a linear function of the fraction of life Fatima (2017), Eq. (3) starting at the ultimate level, equal to unity, corresponding to pipes at less than 10 ° C. (3) This discovery shows that MTBF behaves in proportion to the harmful effect of micro cracks created in the material and their impact on CPVC structures as illustrated in the following figure: MTBF = - β +1