88 CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
TABLE 6.1 Advantages and disadvantages of different penstock materials
MATERIAL
Steel
OCCURRENCE
Most common
ADVANTAGES
• Very widely available
• Pipes can be rolled to almost any size
• Can go up to almost any thickness
• Easy to join and can with stand high
pressure
HDPE
eters,
in
Fairly common • Does not corrode
• Light and hence easy to transport
• Flexible (accommodates small bends)
• Low surge requirement
PVC
Common in
other countries
but not yet
used in Nepal
• Does not corrode
• Light
• Easy to install (solution available)
DISADVANTAGES
• Heavy, transport cost can be
high
• Rigid, bends have to be
specially fabricated at work
shop
• Has corrosion problems
• Can be expensive
• Can have high surge
requirement
• Difficult to join (solvent not
available)
• Available in discrete diam-
maximum diameter available
Nepal is 315 mm OD
• Must be buried (due to ultra
violet (UV) and thermal
degradation) and carefully
backfilled.
• Limited pressure ratings
available in Nepal (up to 10 kg/
cm2 which is 100 m head)
• More expensive than mild steel
for large diameters and high
pressures
• Brittle, can be damaged during
transportation
• Must be buried (due to UV and
thermal degradation) and
carefully backfilled.
• Unsuitable in freezing condi
tions to join pipes)
• Not available in diameters
larger than 250 mm in Nepal
• Limited pressure ratings
available in Nepal (up to 10 kg/
cm2 = 100 m head)
• More expensive than mild steel
at high pressures