How to Prevent Sight Glass Failure

Thermal Shock

Rapid temperature changes — from cold startup, steam condensate, or process upsets — create differential thermal stress in the glass. Borosilicate glass (the most common type) can withstand gradual temperature changes but fails under sudden ΔT exceeding 100°F. Tempered glass is more resistant but still vulnerable.

Pressure Cycling

Repeated pressure cycles fatigue the glass over time. Each cycle creates micro-cracks that propagate until catastrophic failure. High-cycle applications (pressure relief, batch processes) require more frequent glass inspection and replacement.

Chemical Attack

Alkalis (caustic, amines, phosphates) attack borosilicate glass aggressively — even at low concentrations. Hydrofluoric acid dissolves glass entirely. Fluorosilicate glass or mica windows are required for these services.