The glycol evaporator is the key equipment of the Purified Terephthalic Acid (PTA) unit to control the glycol component concentration by evaporation of water. The operation medium includes glycol, water, and a small quality of corrosive impurity, which causes the glycol evaporator to fail; the solution is to select the optimal vessel material such as the 20R, the 304, or the 316L steel. Based on the basic failure mechanism of the glycol evaporator, it was concluded that the main failure mechanism included corrosion thinning and stress corrosion cracking due to the corrosive solution. Then the calculation to solution of the failure probability is discussed based on the first order second moment theory and the method recommended by API581 standard, and the failure probability of the three kinds of material evaporator with the same operating condition and the different inspection effectiveness is carried out. From these figures, it is found that the stainless steel 316L is the best suitable material, and it is shown that the material selection based on the reliability index is a feasible verification method.

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