What is the effect of increased roughness on the carrying capacity of pipes?

• A. carrying capacity increases
• B. carrying capacity decreases
• C. carrying capacity unaffected
• D. depends on velocity

Answer: (B)

Roughness increases friction losses in the pipe, which limits how much fluid can be carried. When the pipe wall is rougher, the friction factor rises, causing more head loss per unit length. With a fixed driving force (like a set pressure difference or pump power), more energy is consumed overcoming that friction, leaving less energy available to push the fluid through, so the maximum flow rate—the carrying capacity—decreases. This trend holds across typical operating ranges, so higher roughness does not boost capacity and is not usually neutral; it reduces it.