Acidic/caustic alternating corrosion on carbon steel pipes in heat exchanger of ethylene plant

Abstract

Caustic embrittlement, a kind of stress corrosion cracking (SCC), is always encountered on materials under stresses amid caustic environment. Acidic corrosion is another familiar degradation on materials contacting acidic media. However, it has been seldom studied what effect would be resulted in on materials that are exposed to an acidic/caustic alternating environment. In this paper, failure events were discovered on the carbon steel pipes under such an alternating service condition due to frequent sharp fluctuations of the heat medium's (process water) pH values in a heat exchanger. What is more, even chloride ions and sulfur element were detected, i.e., pitting corrosion was involved as well. In order to identify the causes of the failure, matrix materials of the pipes were examined, failure defects on pipe surfaces were investigated, particularly the process water was thoroughly inspected via a series of characterization methods. Based on the analysis results, a novel four-level mechanism from microscopic scale to macroscopic scale was tentatively proposed to explain such an acidic/caustic alternating corrosion.

Failure analysis on synergistic effect of erosion and corrosion on failed fittings in specialty chemical plant. Part I: Elbows

“…The second one is the adsorption theory involving the competition between Cl − and O 2− . As shown in Figure b, the local absorbed species may lead to local thinning and increase the local electric field strength, which eventually results to the formation of pits . The third one is a film‐breaking mechanism (shown in Figure c).…”

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

“…Consequently, the hydrogen atoms will first be absorbed by the TiO 2 , even composing metastable compounds TiO(OH) [Equation (9), [28]] if their contents continuously increase. Then, Zeng et al [28] thought that the hydrogen atoms in TiO(OH) will serve as the electron donors to produce hydrogen ions, the reverse reaction of Equation (8). However in our opinion, these hydrogen atoms will be mutually coupled and form hydrogen gases H 2 , Equation (10).…”

“…Materials quality, equipment operation, service environment, routine maintenance, or other factors, which were the main causes for inducing these premature failures in these cooling equipment, were urgently investigated. Consequently, in order to immediately identify the causes of such failures, investigations into four aspects were carried out by referencing our previous successful failure analysis experiences [7][8][9], including matrix materials, environmental media, operation conditions, installation, and maintenance. Based on the leaked tubes and the environmental media as seawater, desalinated water, etc., over 10 kinds of characterization methods were conducted for failure analysis in series of totally two parts, and totally seven kinds of different failure mechanisms were simultaneously detected.…”

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.…”