Compatibility Guidelines for Glass-Lined Reactors

Conclusion

While glass-lined reactors provide outstanding corrosion resistance under most acidic and neutral conditions, certain chemicals and process environments can degrade the enamel and shorten equipment life. Awareness of these limitations—particularly with strong alkalis, fluorides, and dry or high-temperature operations—ensures safe, reliable, and long-term reactor performance.

Glass-lined reactors are widely used in the chemical industry because their enamel coating provides excellent corrosion resistance and chemical inertness across a broad range of media. However, certain environments can attack or mechanically damage the glass lining through mechanisms such as leaching, alkali attack, or stress cracking. The following sections outline chemical classes and conditions that require particular caution when using glass-lined equipment.

1. Strongly Alkaline or High-pH Solutions

Examples: Sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonia solutions, alkaline cleaning agents

Mechanism: Strong bases attack the silica network of the glass, leading to surface roughness, dulling (loss of gloss), and eventual pinhole formation. The rate of attack increases with temperature and concentration.

2. Hydrofluoric Acid (HF) and Fluoride Compounds

Examples: Hydrofluoric acid, ammonium fluoride, sodium fluoride

Mechanism: Fluoride ions react rapidly with silica, etching and destroying the glass surface even at very low concentrations. Glass-lined reactors are unsuitable for any HF- or fluoride-containing processes.

3. Hot Concentrated Phosphoric or Sulfuric Acids

Mechanism: At high temperatures and concentrations, these acids can induce stress cracking and corrosion of the enamel. Lower concentrations and moderate temperatures are generally safe.

4. Molten Salts or Metals

Mechanism: Molten materials can cause both physical erosion and chemical attack on the enamel, particularly at elevated temperatures where diffusion and reaction rates increase.

5. Strong Reducing Agents

Examples: Metallic sodium, lithium aluminium hydride (LiAlH₄), hydrazine

Mechanism: These reagents can react violently with residual moisture and may attack the glass at defect sites, compromising the enamel integrity.

6. Abrasive or High-Solids Slurries

Mechanism: Mechanical erosion can occur when abrasive particles are present, especially under high agitation speeds or during dry operation. Such wear can lead to localised thinning of the glass layer.

7. Processes Involving High Static Charge or Dry Gas Phases

Mechanism: Electrostatic discharge can cause micro-pitting or pinhole defects in the enamel surface. Proper grounding and humidification of the process atmosphere help minimise this risk.

8. Hydrochloric Acid (>20% or >80°C)

Mechanism:

• HCl dissolves silica and leaches alkali ions from the glass matrix.

• High vapor pressure and dry HCl gas can attack glass even more aggressively than aqueous acid.

• Prolonged exposure leads to loss of gloss, increased surface roughness, and reduced dielectric strength—precursors to enamel failure.

Recommendation: For concentrated or hot HCl service, use tantalum-lined or PTFE-lined reactors instead of glass-lined vessels.

Equipodia is a specialist of glass-lined process equipment. Customers are deemed to have full knowledge of their processes and the characteristics of the materials involved in such processes. It is the customer's responsibility to determine the suitability of any construction material for their intended application. If there is any uncertainty regarding material selection, customers are strongly advised to perform all necessary corrosion and compatibility testing prior to placing an order. While technical assistance may be provided upon request, such assistance is offered for informational purposes only and does not constitute a guarantee or warranty. The final selection and approval of construction materials shall be the sole responsibility of the customer.