Pipe marking color Green corresponds to which substance?

• A. Hydraulic Oil
• B. Fuel Oil
• C. Seawater
• D. Fresh Water

Answer: (C)

Pipe marking color coding is a quick visual cue that tells you what fluid is in a line, which helps prevent mistakes during maintenance and operation. In this Navy scheme, green marks denote seawater. That means a pipe with green markings is carrying seawater, such as in cooling, ballast, or other seawater systems on the ship. Fresh water, hydraulic oil, and fuel oil use different colors, so they wouldn’t be green. The green designation for seawater helps sailors verify the line at a glance and reduces the risk of cross-connecting or servicing the wrong system.