Pipe materials — relative flow quality / hydraulic smoothness ranking Based on internal smoothness and resulting hydraulic performance (carrying capacity), which sequence is correct from lower to higher flow quality?

Introduction / Context:
Hydraulic smoothness affects head loss and capacity. Designers often rank pipe materials by roughness to select diameters and pumps economically. Understanding relative internal surface characteristics is essential for water supply and drainage systems.

Given Data / Assumptions:

• C.I. (cast iron) is comparatively rougher internally.
• G.I. (galvanized iron/steel) is smoother than C.I. but can scale.
• A.C. (asbestos cement) is hydraulically smoother than steel/iron.
• PVC is very smooth among common choices.

Concept / Approach:
For a given diameter and flow, head loss hf depends on roughness through friction factor. Lower roughness → lower hf → better “flow quality.” Thus, arranging materials from rough to smooth yields the correct engineering sequence.

Step-by-Step Solution:
Identify roughest: C.I. → aged surfaces develop tuberculation.Next: G.I. → smoother initially, but susceptible to scaling over time.Next: A.C. → cementitious, smoother hydraulically than ferrous materials.Smoothest: PVC → very low roughness, excellent carrying capacity.Therefore: C.I. → G.I. → A.C. → PVC.

Verification / Alternative check:
Compare typical absolute roughness values used in design tables; the ordering aligns with standard references and Hazen–Williams C-coefficients (PVC highest C).

Why Other Options Are Wrong:
Any ordering that places A.C. or PVC as rougher than iron/steel contradicts standard hydraulic data.

Common Pitfalls:
Ignoring aging effects (scaling, biofilm) on metallic pipes; mixing “strength” with “smoothness”; and using wrong C-values in spreadsheets.

Final Answer:
C.I. pipes → G.I. pipes → A.C. pipes → PVC pipes