Technical Selection of Penstock Material for Hydro-Electric Pumped Storage Piping System

REPORT ON TECHNICAL SELECTION OF PENSTOCK MATERIAL
FOR HYDRO-ELECTRIC PUMPED STORAGE PIPING SYSTEM
PREPARED BY: ENG XYZ
DATED:

Contents
1. Introduction..................................................................................................................3
2. Design and Selection................................................................................................... 4
Design data.............................................................................................................4
Design of the two steel material ........................................................................
Fracture Assessment ...........................................................................................
NDT methods.......................................................................................................
3. Sensitivity Test............................................................................................................11
Lifetime assessment............................................................................................12
Revised assessment.............................................................................................14
4. Fatigue Assessment...................................................................................................14
5. Conclusion...................................................................................................................15

1. INTRODUCTION
Hydraulic pumped storage stations present a complementary solution to the irregular power demands
across the United Kingdom. They are usually integrated such that during peak demands, especially in
winter season when power consumption escalates, people can still get sufficient power that is minimally
interrupted. In this report, a critical portion of the system (as shown in figure 3) is to be designed such
that appropriate material for its construction can be selected. Notably, this component is the penstock pipe
which conveys high pressure water flowing between the two reservoirs. To minimize costly failures, and
ensure durability in service, this component must withstand various pressure scenarios and regimes. For
instance, it must withstand the water hummer phenomenon and other hydraulic loss elements.
Additionally, the walls must have adequate structural integrity to resist the stresses induced by the
internal pressures due to the flowing water. Therefore, the aim of this report is to present two distinct steel
materials for selection based on the design constraints and given parameters. Additionally, a review of
their fatigue life will be undertaken

2. DESIGN AND SELECTION
2.1 Design Data Provided
Table 1: Design Parameters
Crack length (mm) Pipe diameter (m) Static head (m) Water hummer (m)
3.0 2.5 501 765
Table 2: Steel Material Properties
PROPERTIES STEEL A QT 445 STEEL B BS150490LT50
C 0.15-0.21 <0.20
Si <0.90 0.10-0.50
S <0.04 <0.03
P <0.04 <0.03
Mn 0.80-1.10 0.9-1.60
Cr 0.50-0.80 <0.25
Mo 0.25-0.60 <0.10
Ni - <0.30
Zr 0.05-0.15 -
Cu - <0.30
B 0.0005 -
Nb - 0.01-0.06
Yield strength (MPa 700 350
UTS (MPa) 800 500
Fracture toughness Kic 100 130
Elongation (%) 18 20
Price of rolled plate (per
1000kg
965 525
Density (kg/m3) 9750 9750
2.2 Design of the two steel Material
It is noted that the maximum allowable stress (for the purpose of determining the thickness of
both steel materials) is fixed at 0.6 times the material yield strength. The penstock is normally
built in a similar fashion as the pressure vessels. Consideration is given for the thin walled
cylinders hence theories of hoop and circumferential stresses come in handy in this case: