Pitting corrosion on 316L pipes in terephthalic acid (TA) dryer

Abstract

Grade 316L is a type of austenitic stainless steel with ultra-low carbon content and it exhibits superior corrosion resistance. However, pitting is always observed in 316L steel when it is exposed to media containing halide ions. In the present study, we found that in the presence of acetate acid (HAc) containing chloride or bromide ions, pitting occurred on the surface of the rotary steam pipes with the matrix material of 316L steel in terephthalic acid (TA) dryer. In order to identify the causes of the failure, metallographic structures and chemical compositions of the matrix material were inspected by an optical microscope (OM) and a photoelectric direct reading spectrometer. Beside these, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) as well as ion chromatography (IC) were used to analyze the micromorphologies of the corrosion pits and the chemical compositions of the corrosion deposits within them. Analysis of the results revealed the sources of halide ions and the factors accelerating the corrosion rate. Beside these, detailed mechanisms of pitting were discussed and six out of all the seven theoretical morphologies of pitting features were obtained in practice.

A comprehensive approach based on SVM to model pitting corrosion behaviour of EN 1.4404 stainless steel

“…In addition, the minimum value tested for g, provided the worst results in both precision and accuracy terms. In this case, the maximum value of precision (0.96) is reached using g ¼ 2 4 , 2 5 and 2 6 with C ¼ 2 3 , 2 5 and 2 7 , respectively, whereas maximum accuracy result (0.87) is obtained using g ¼ 2 1 and C ¼ 2 7 . These models are represented with white points in Fig.…”

“…This parameter is related to pitting corrosion resistance of the material under study. However, polarisation tests applied to assess pitting corrosion behaviour involve two principal steps: the interpretation of the polarisation curve and the microscopic analysis of the material surface to evaluate pits Friedman þ Fisher LSD 0.96 precision g ¼ 2 2 , C ¼ 2 À1 , 2 0 , 2 1 , 2 3 g ¼ 2 3 , C ¼ 2 0 , 2 1 , 2 3 , 2 5 g ¼ 2 4 , C ¼ 2 3 , 2 5 , 2 7 g ¼ 2 5 , C ¼ 2 5 , 2 7 g ¼ 2 6 , C ¼ 2 7 Friedman þ Fisher LSD 0.87 accuracy g ¼ 2 0 , C ¼ 2 5 , 2 7 g ¼ 2 1 , C ¼ 2 3 , 2 5 , 2 7 g ¼ 2 2 , C ¼ 2 3 , 2 5 , 2 7 g ¼ 2 3 , C ¼ 2 5 , 2 7 g ¼ 2 4 , C ¼ 2 7 Figure 7. ROC space for the optimal classification models based on BC and SVMs formation.…”

“…Pitting corrosion has been considered one of the most critical types of localised corrosion that can lead to failure of structural components affecting their service life [5]. Many authors have developed studies about this phenomenon [6][7][8]. Some of them have been focused on analysing the influence of environmental factors on corrosion behaviour, concluding that principal environmental variables affecting corrosion behaviour are chloride ion concentration, pH and temperature [9][10][11].…”

Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: Electrochemical corrosion

“…As a result, seawater was provided with access into the shell side from the inlet of the tubes, and simultaneously introducing chloride ions. Then, these chloride ions would particularly accumulate in the gaps between the 78 mm-thick tube sheet and the titanium tubes, and gradually concentrate on the outside wall surfaces of the titanium tubes under the gaps, eventually initiating crevice corrosion [23] as well as galvanic corrosion. Actually, crevice corrosion is a common degradation on titanium, and has already attracted a wealth of researches to identify its influencing factors [24].…”

Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part II: Mechanical degradation

“…Consequently, based on our past successful failure analysis experiences [3][4][5][6], systematical study was carried out in series of two parts. The previous Part I [7] primarily focused on scope of electrochemical corrosion, such as galvanic corrosion, crevice corrosion, and their interaction effect on the initiation of hydrogen-assisted corrosion including hydrogen blistering and hydrogen embrittlement.…”