In corrosive service, the reliability of a plate heat exchanger system depends on the material compatibility of every component in contact with the process medium. Heat transfer plates, sealing gaskets and connecting piping are all exposed to the same fluid under similar conditions, yet they are frequently specified independently. This article reviews the selection of these three component groups and explains why they should be specified as a single system.
Selection Parameters
Material selection in corrosive service is governed by a defined set of process parameters:
- Chemical composition and concentration of the process medium
- Operating and peak temperatures
- Operating and peak pressures
- Flow velocity and fouling tendency
Corrosion rates generally increase with temperature and concentration, and certain combinations — such as chlorides combined with elevated temperature — accelerate specific failure mechanisms, including pitting and stress corrosion cracking. These parameters should therefore be established in advance and applied consistently to all components in the fluid path.
Plate Materials
Heat exchanger plates are produced from a limited range of materials, each with a defined field of application.
Stainless steel (AISI 316/316L). Stainless steels of the 316 family are the most widely used plate materials. They provide good heat transfer, formability and corrosion resistance in neutral and mildly corrosive media, and represent the most economical solution for a large share of industrial applications. Their principal limitation is susceptibility to pitting and stress corrosion cracking in chloride-containing environments, particularly at elevated temperatures.
Titanium. Titanium plates are specified where chloride concentration or temperature exceeds the capability of stainless steel. Titanium offers outstanding resistance to chloride attack, including seawater and concentrated brines, and is commonly applied in coastal installations, marine systems and chemical dosing circuits.
Nickel-based alloys. For highly aggressive acids and strongly oxidizing media, nickel-based alloys provide the required resistance where stainless steel and titanium would fail prematurely. Their higher material cost is justified in applications where alternative materials cannot provide an acceptable service life.
The selection of plate material should be based on the actual medium, its concentration and the maximum operating temperature, rather than on general assumptions about the application.
Gasket Materials
Gaskets seal the plate pack and separate the two fluid circuits. Because gasket materials are elastomeric, they are subject to aging under temperature and chemical exposure, and they are typically the first components in a plate heat exchanger to require replacement.
NBR (nitrile rubber) is suitable for mineral oils and general industrial fluids at moderate temperatures. EPDM offers good resistance to water, steam, diluted acids and alkalis, and is widely used in water treatment and mild chemical duty. FKM (fluororubber, Viton-type) provides higher temperature resistance and broader chemical compatibility, including many acids and hydrocarbons. PTFE-based gaskets are available for the most demanding media, offering resistance to a very wide range of chemicals.
Gasket material must be compatible with the process medium across the full operating temperature range. Where the medium attacks the gasket, swelling or hardening occurs, the sealing force is reduced, and leakage or cross-contamination between circuits can result. Periodic inspection and scheduled replacement of gaskets are standard maintenance practice for plate heat exchangers.
Connecting Piping
The piping that connects the heat exchanger to the process circuit is exposed to the same medium and should be selected on the same basis as the exchanger itself. In corrosive service, metallic piping is subject to localized corrosion at flanges, welds and threaded joints, where crevices and residual stress promote attack. Such failures can develop gradually and may affect surrounding equipment before they are detected.
Thermoplastic piping materials, including PVC, CPVC, PPH and PVDF, are established solutions for corrosive fluid handling. Among these, PVDF is characterized by good resistance to many strong acids, oxidizing agents and chlorinated media, combined with a comparatively wide service temperature range for a thermoplastic. Flanged and socket connections can be matched to the nozzle configuration of the heat exchanger, allowing the piping system to be integrated with the unit on the same corrosion basis. If needed, you can choose XITA PVDF piping system to keep the complete fluid path corrosion-resistant.
System-Level Material Matching
A common error in the design and maintenance of corrosive heat exchange systems is to evaluate individual components in isolation. Selecting corrosion-resistant plates does not ensure that the gaskets, valves and piping in the same circuit are suitable for the same medium. The complete fluid path should be reviewed against a single set of process data.
This principle applies to new installations and to replacement programs alike. In a replacement program, for example, new plates should be paired with gaskets and piping that are compatible with the same medium, temperature and pressure; otherwise, the weakest component determines the service life of the system.
Replacement Plates and Gaskets
For existing heat exchangers, compatible replacement plates and gaskets can restore full performance without replacing the complete unit. Before ordering, the following information should be confirmed: the heat exchanger model, plate quantity, plate material and thickness, gasket material, and the operating conditions of the application. Senovis PHE supplies replacement plates and gaskets for major brands including Alfa Laval, GEA, SWEP, Sondex, Vicarb, FUNKE and API, matched to the original specification of the unit.
Conclusion
The service life of a plate heat exchanger in corrosive applications is determined by the compatibility of the complete fluid path — plates, gaskets and connecting piping — with the process medium. When these components are selected against the same process parameters and reviewed as one system, maintenance becomes more predictable and the overall service life of the installation is extended.
