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Corrosion
Parallel pin expansion may reduce corrosion risk
Material selection is a critical factor for heat exchangers working in corrosive applications , but tube expansion methods may also play a role in tube life . Premature tube failure is one of the leading causes of downtime in the field , accounting for 47 % of lost production opportunities ( Stewart , M . & Lewis , O ., 2013 ). Stress corrosion cracking is a common tube failure mode in corrosive environments , impacting any number of tubes in a vessel . While stress corrosion can be difficult to identify in the field , there may be a way to reduce the likelihood of occurrence by changing the tube expansion method .
Content adapted from research presented by : Ben Lambers & John Papie , Elliott Tool Technologies
Background In 2023 , Elliott Tool Technologies was approached by a Heat Exchanger Fabricator with questions about a new Titanium marine vessel they put into service a year prior . Several of the tube ends were severely damaged and cracked along the expanded ID of the tube . It was determined that this failure was likely caused by stress corrosion cracking as a result of the expansion process .
Stress corrosion cracking Stress corrosion cracking is a type of fracturing that occurs in metals due to a combination of tensile and residual stress in a corrosive environment . This can occur in stainless steel , titanium , and Inconel materials , impacting any number of tubes in a vessel . Tube failure related to stress corrosion cracking will often result in retubing , as the tube is often too brittle to be plugged or repaired by other means . Two types of stress corrosion cracking are intergranular , when cracks develop along grain boundaries , and transgranular , where the crack forms through the grains of the material .
Figure 1 . Undeformed area of 304 stainless steel . Image courtesy of Elliott Tool Technologies .
Figure 2 . Deformed area of 304 stainless steel . Image courtesy of Elliott Tool Technologies .
28 Heat Exchanger World February 2025 www . heat-exchanger-world . com