500NB MSGL manhole with sight glass

500NB: This refers to the nominal bore (NB) size of the manhole. In this case, it’s 500 millimeters (mm) in diameter. MSGL: This stands for “Mild Steel Glass-Lined”. It indicates that the manhole is made from mild steel and has a glass lining on the inside. Glass lining provides excellent resistance to corrosion, mechanical shocks, and abrasion. It also ensures smooth, non-stick properties and inertness. Manhole: A manhole is an access point or opening in a vessel or tank. It allows personnel to enter for maintenance, inspection, or cleaning purposes. Sight Glass: The sight glass is a transparent window integrated into the manhole cover. It allows operators to visually inspect the contents of the vessel without opening the cover. This is especially useful for monitoring processes or checking levels.