WBPSC AE (PWD) 1998
⭕ A. 130
⭕ B. 110 to 120
⭕ C. 99 to 100
⭕ D. 75 to 90
📚 Explanation:
The Hazen-Williams coefficient (c) for a 20-year old C.I. (Cast Iron) pipe is usually around 99 to 100.
🔹 This value accounts for increased roughness and reduced flow efficiency due to aging.
🔹 Newer pipes typically have higher c values (like 130), but with age, corrosion and scaling reduce it.
The Hazen-Williams coefficient (c) for a 20-year old C.I. (Cast Iron) pipe is usually around 99 to 100.
🔹 This value accounts for increased roughness and reduced flow efficiency due to aging.
🔹 Newer pipes typically have higher c values (like 130), but with age, corrosion and scaling reduce it.
👉 Therefore, the correct answer is: C. 99 to 100
Key Points on Hazen-Williams “c” Coefficient:
- C.I. pipe age effect: 20-year old pipes have reduced c due to roughness.
- New vs. old pipes: New pipes ≈ 130, old ≈ 99–100.
- Flow calculation: Lower c increases head loss in the Hazen-Williams formula.
