Read Consulting, a California materials failure analysis laboratory, has performed failure analysis of a wide variety of sigh glasses. In this case a failed reflex boiler sight glass was analyzed.. Reflex sight glasses are used to read the liquid level in boilers and other process equipment. The liquid level is read directly with the eyes or by means of a camera. On the medium side, grooves are pressed into the reflex sight glass, which make the level clearer and easier to read.
The principle of reflex glass is based on the difference in the refractive indices of liquid and gas or water and steam. The liquid level shows a striking dark color for the liquid space and a bright white color for the empty space. Reflex site glasses are typically made with tempered borosilicate glass.
This failure was caused by damage to the glass edge just below the chamfer. This indicates interference from the steel frame.
