How Do Fluoropolymer Heat Exchangers Resist Stress Corrosion Cracking in Chloride-Bearing Environments?

Stress corrosion cracking of austenitic stainless steels is known to be catastrophic in hot chloride conditions. This effect is fully unaffected by fluoropolymer heat exchangers, which makes them an elegant solution.

Introduction to Stress Corrosion Cracking (SCC)
Stress corrosion cracking (SCC) occurs when a material under tensile stress is exposed to a corrosive environment, such as chlorides, resulting in crack formation. Failure of this kind is particularly susceptible in materials like austenitic stainless steels (e.g. 304 and 316). The combined effect of tension and chloride ions can cause brittle fracture over a period of time, especially at higher temperatures. This is frequent in companies using metals in sea water, brackish water or chlorinated chemicals.

Stress corrosion cracking resistance of fluoropolymers in chloride media
Fluoropolymer heat exchangers like PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxy) are totally resistant to stress corrosion cracking (SCC) in chloride containing media, which makes them a perfect choice of material in corrosive applications. Fluoropolymers are non-crystalline (amorphous or semi-crystalline) and so do not include the grain boundaries that are commonly found in metals such as stainless steel. No grain boundaries and no electrochemical channel for corrosion to propagate. No SCC.

Also, the inertness of fluoropolymers such as PTFE and PFA to chlorides provides additional protection against the harsh effects of chlorine-based chemicals. SCC is not possible in fluoropolymers, there is no electrochemical corrosion mechanism like in metals. This chemical stability allows fluoropolymer heat exchangers to provide long-term, reliable operation in chloride conditions, even at elevated temperatures.

Fluoropolymer Heat Exchangers for Critical Applications in Chloride Bearing Environments
In businesses where seawater cooling systems, brackish water, chlorinated process streams or any other application with even trace levels of chloride contamination exist, the threat of stress corrosion cracking is a serious concern. Fluoropolymer heat exchangers are commonly found in these services because of their resistance to the adverse effects of chloride caused SCC. One of the key drivers for reliability in adopting fluoropolymer exchangers over typical metal exchangers is the absence of the risk of SCC.

Fluoropolymers' resistance to SCC benefits applications like as desalination plants, chemical manufacturers, and maritime cooling systems, ensuring safe and reliable performance of heat exchangers for long periods, even under difficult environmental circumstances.

Technical Issues
PTFE and PFA are completely immune to all types of electrochemical corrosion. Fluoropolymers are chemically inert and do not have any grain boundaries and are suited for extremely corrosive services where metals would normally fail owing to stress corrosion cracking. In fact, the choice of fluoropolymer heat exchangers is often dictated by the requirements of dependability and safety, not solely by capital cost. These materials help systems to survive in conditions where typical metallic exchangers would incur costly repairs or unscheduled downtime.

Comparative SCC Susceptibility of Common Exchanger Materials
Material SCC SusceptibilityMain features
304 SS High Chloride SCC at elevated temperatures a concern
316 SS Moderate Better resistance but still vulnerable in strong chloride conditions
Duplex SS Low to moderate More resistance to SCC than austenitic grades
PTFE/PFA None Complete resistance to chlorine SCC
Conclusion 
The stress corrosion cracking resistance of fluoropolymers such as PTFE and PFA in chloride conditions offers a significant advantage in applications where reliability and safety are important. These materials offer extended predicted equipment life in difficult environment without the possibility of catastrophic failures owing to SCC. Understanding failure mechanisms like stress corrosion cracking is vital to choosing good material selections for heat exchangers in corrosive environments. Fluoropolymer heat exchangers are a trusted solution in industries where tiny amounts of chlorides represent a major threat to metallic equipment.