Global Processing

Sight glass safety guidelines

September 12, 2005

A standard “bolt-on” design is among the most common sightglass configurations.

1. Maintenance — Never reuse any glass or gaskets

  • Once a standard-design sightglass has been removed from its mounting, regardless of the reason for removal, discard the glass and gaskets and substitute a new glass and gaskets.
    An exception: Very often, Metaglas® safety windows may be reinstalled, following instructions provided for this procedure.
  • Keep glass clean using commercial glass cleaners.
  • Never use wire brushed, metal scrapers or harsh abrasives.
  • Do not attempt to clean glass while equipment is in operation.

An exception to the general rule: Metaglas safety windows can often be reinstalled.

2. Inspection — Sightglasses should be regularly inspected for damage
  • To examine for scratches, shine a very bright concentrated light source at an angle of about 45°. Anything that glistens should be inspected closely.
  • Scratches that catch the fingernail and any star or crescent-shaped marks that glisten are cause for replacement.
  • Sightglasses that appear cloudy or roughened after cleaning should be replaced.
  • Also inspect sightglass frames/flanges for corrosion buildup.

3. Installation — Never use damaged glass

  • Never use glass that is scratched, chipped or otherwise damaged.
  • Glass mating surfaces must be flat within 0.127 mm with a smooth finish.
  • Flanges must be rigid.
  • Do not allow the glass to contact metal when assembling.
  • Gaskets must be new, clean and smooth.
  • Use gaskets of the same diameter and fit them concentrically.

4. Bolting — Never tighten bolts on a sightglass while plant is operating

  • Follow a regular tightening sequence to ensure even loading of glass.
  • Allow a maximum difference of 2Nm (1.5 ft/lbs) between bolts during tightening.
  • Tighten only enough to vie a positive seal against the process pressure.
  • Bolts may need tightening after initial cycling of vessel.
  • Never tighten bolts when the sightglass is hot.
These guidelines are based on acknowledged best practice. L.J. Star shall not be liable for glass damage, failure or any resulting consequences.
For a reprint of these safety guidelines, or to get additional information click on the "More Information" link below. If you want a printed copy mailed to you, please include your address information.