Electrostatic Discharge: A Hidden Threat to Glass-Lined Vessels

Glass-lined vessels are widely used in chemical and pharmaceutical manufacturing because of their corrosion resistance, durability, and cleanability. However, despite their strength, they are not immune to damage. One of the most overlooked failure mechanisms is Electrostatic Discharge (ESD), a silent but destructive force that can compromise both equipment integrity and process safety.

What is Electrostatic Discharge (ESD)?

Electrostatic Discharge occurs when static electricity accumulates in a liquid or on a surface and suddenly discharges. In glass-lined vessels, ESD is typically generated by:

· Agitation of non-conductive solvents (e.g., heptane, toluene, xylene) against vessel walls and agitator blades.

· Fluid transfer through ungrounded dip pipes, where solvent velocity charges the liquid stream.

· Prolonged agitation at low conductivity, allowing charges to build without a path to dissipate.

The result is a “brush discharge,” a localized, high-energy spark that penetrates the glass coating. Because the dielectric breakdown voltage of chemical process glass is ~500 volts/mil, a 40-mil coating would require >20,000 volts to break down. Such voltages are achievable in poorly grounded, non-conductive systems.

How ESD Damages Glass-Lined Equipment

ESD failure is characterized by microscopic pinholes or chips in the glass surface. Though often invisible to the naked eye, these defects can be detected with spark testing. Over time, pinholes allow corrosive fluids to reach the steel substrate, resulting in:

· Corrosion and undercutting of the lining.

· Contamination of product, critical in regulated industries like pharmaceuticals.

· Reduced service life of vessels and agitators.

· Unplanned downtime and costly repairs.

In a case study of a Pfizer R15 reactor inspected by Glasslined Technologies, ESD was identified as the root cause of glass damage. Pinholes were concentrated on the bottom head and agitator blade tips, areas subject to high shear and turbulence. The contributing factors included:

· Use of heptane, a low-conductivity solvent (~10⁻¹³ S/m).

· Ungrounded Hastelloy dip pipe charging liquid as it entered the vessel.

· Agitator speeds up to 300 RPM, increasing solvent velocity and static buildup.

· Prolonged agitation of non-conductive liquids, in some cases up to six days.

Prevention Strategies

Preventing ESD damage in glass-lined vessels requires both process and equipment controls. Industry best practices include:

• Grounding and Bonding

  • Ensure dip pipes, flush valves, and accessories are properly grounded.

  • Use static-dissipative fittings when working with non-conductive solvents.

• Process Adjustments

  • Reduce solvent transfer velocities to <1 m/s to minimize charge generation.

  • Allow relaxation time for solvents before restarting agitation.

  • Limit agitator RPM when processing low-conductivity liquids.

• Equipment Considerations

  • Inspect vessels regularly for white spots or pinholes, especially on agitator tips and bottom heads.

  • Consider anti-static glass formulations for processes with persistent ESD activity.

  • Maintain spark testing schedules to detect sub-visible defects.

Permanent Repair Solutions

While prevention is essential, once ESD damage occurs, temporary fixes won’t suffice. At Glasslined Technologies, we provide permanent glasslined repair solutions that restore equipment to original specifications. These repairs eliminate pinholing, extend vessel life, and help prevent future failures.

Conclusion

Electrostatic Discharge may be invisible, but its consequences are very real. By understanding its causes, recognizing its effects, and implementing proactive safeguards, manufacturers can protect both their equipment and their product integrity.

Key takeaway: Even the most durable glass-lined vessels can suffer catastrophic damage from ESD, but with proper design, grounding, and permanent repair solutions, the risk can be controlled. 

References

1.        GTI Pfizer R15 Report, Glasslined Technologies, 2016.

2.        Pfaudler, Inc. SB95-910-4: Best Practices for Avoiding Damage in Glass-Lined Equipment.

3.        De Dietrich Process Systems. 3009 Glass Technical Data Sheet.

4.        McKinley, K., Evele, H., Baldwin, C. Analysis of Fracture in Porcelain Enamels. Ferro Corporation.

5.        Pagliuca, S., Faust, W.D. The Preparation, Application and Properties of Enamels.