How do brazed aluminum heat exchangers corrode?

Brazed aluminum heat exchangers in LNG plants are susceptible to corrosion through several mechanisms, primarily related to the presence of contaminants in the process streams or the environment. One major type of corrosion is pitting corrosion, which occurs when chlorides or other aggressive ions attack the aluminum alloy, creating small, localized pits on the surface. These pits can eventually lead to leaks or structural failures. Another form of corrosion is galvanic corrosion, which occurs when dissimilar metals are in contact in the presence of an electrolyte. Although brazed aluminum heat exchangers are primarily aluminum, there may be small amounts of other metals present in the brazing alloy or in contact with the aluminum, creating galvanic couples. If moisture or other electrolytes are present, this can lead to accelerated corrosion of the aluminum. Crevice corrosion can occur in the narrow crevices between the fins and plates in the heat exchanger. These crevices can trap contaminants and create stagnant areas where corrosion can occur more rapidly. Furthermore, corrosion can be exacerbated by the presence of mercury. Even trace amounts of mercury can cause liquid metal embrittlement (LME) of aluminum alloys, weakening their structure and making them more susceptible to corrosion and cracking. Proper feed gas pretreatment is crucial to remove contaminants such as chlorides, mercury, and moisture to minimize corrosion in brazed aluminum heat exchangers. Regular inspections and maintenance are also essential to detect and address any signs of corrosion before they lead to major problems. This includes monitoring the process streams for contaminants and performing visual inspections of the heat exchanger surfaces.