Which of the following is a factor in gas pipe sizing?

• A. Ambient humidity
• B. Specific gravity of gas
• C. Pipe color
• D. Maximum gas pressure rating

Answer: (B)

Gas pipe sizing hinges on calculating the pressure drop and flow through the piping. The density of the gas, expressed as specific gravity relative to air, directly affects how much pressure is lost as gas moves through a given length and diameter. A denser gas (higher specific gravity) carries more mass for the same volumetric flow, leading to greater friction and a larger pressure drop. To keep the required pressure at the appliance, the pipe size may need to be increased, so specific gravity is a key factor in sizing calculations. Ambient humidity, pipe color, and the system’s maximum pressure rating don’t drive the sizing calculation: humidity doesn’t noticeably change gas flow, color is just marking, and rating considerations relate to safety limits rather than determining the diameter.