Heat Exchanger Material Selection: Chemical Compatibility by Industrial Application

Material selection is the engineering decision with the greatest impact on a heat exchanger's lifecycle cost and reliability. An inappropriate material leads to accelerated corrosion, process contamination or premature failure; an over-specified material drives unnecessary cost. This guide provides a structured starting point for engineering, procurement and technical management teams.

1. Standard materials: application range and key characteristics

Industrial heat exchangers are typically manufactured in a spectrum of materials covering the majority of process applications. Each presents a distinct profile of chemical, mechanical and thermal resistance.

2. Key factors determining compatibility

A material's chemical resistance is not a fixed value: it is a function of several variables interacting simultaneously in the real process. Any extrapolation beyond the documented conditions range requires specific validation.

• Temperature: Corrosion accelerates exponentially with temperature. A material compatible at 20 °C may be unsuitable at 80 °C for the same fluid.
• Fluid concentration: Acids and bases exhibit non-linear behaviour. Stainless steel, for instance, resists high concentrations of nitric acid but not intermediate ones.
• Chloride content: Pitting and crevice corrosion in stainless steels is particularly sensitive to Cl⁻ concentration and temperature.
• Fluid velocity: Erosion-corrosion and cavitation are velocity-dependent. Copper, for example, has velocity limitations in seawater service.
• pH and redox potential: These determine the passivation or active attack zone on the material's Pourbaix diagram.
• Contaminants and trace impurities: Unexpected compounds (sulphides, oxidants, metal ions) can drastically alter material behaviour even at trace concentrations.

3. Compatibility table by fluid and sector

The table covers the most common process fluids and compounds across the main industries using industrial heat exchangers, indicating materials for which documented compatibility exists under representative conditions. Empty cells indicate absence of standard-condition compatibility data, not necessarily incompatibility.

4. Special cases: where standard materials are insufficient

Certain applications involve combinations of corrosivity, temperature and regulatory requirements that exceed the performance of standard materials. BOIXAC has established experience in the following:

• Seawater and chlorinated media: Grade 2 titanium and 90/10 cupronickel provide crevice corrosion and biofouling resistance that AISI 316 cannot reliably guarantee under prolonged high-salinity exposure.
• Concentrated oxidising acids: Hastelloy C-276 is the reference material for hydrochloric acid, mixed acid environments and reducing conditions. Hastelloy B-3 for purely reducing media without oxidants.
• High-specification pharmaceutical and food processing: AISI 316L (low carbon) with electropolished or machined finish Ra < 0.8 µm meets FDA/EHEDG requirements. AISI 310 is used in special cases at temperatures above 650 °C.
• Petroleum and hydrocarbons with H₂S: Titanium and select Hastelloy grades resist sulphide stress cracking (SSC) under NACE MR0175 conditions.

5. Recommended material selection methodology

Material selection for an industrial heat exchanger follows a structured process combining compatibility table reference with detailed analysis of the specific case.

• Characterise the process fluid: full composition, pH, maximum and minimum operating temperature, pressure, presence of solids or impurities.
• Consult corrosion literature (ASTM G31, Corrosion Engineers databases, alloy manufacturer data sheets).
• Consider applicable standards: FDA 21 CFR, EHEDG, ATEX, NACE MR0175, PED 2014/68/EU, AD-2000.
• Evaluate lifecycle cost: material cost versus maintenance cost, expected service life, cost of unplanned shutdown due to failure.
• Engage the heat exchanger manufacturer with the above data for final validation.