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HDPE Pipe-Polyethylene Water Pipes & Fittings
Calculation Methods 1. CALCULATING WALL THICKNESS Pipe calculation formula in ISO 161-1 is used in order to calculate wall thickness.
The long forms of the symbols in this Formula are as follows: PN
Normal Pressure
(Bar)
s
Wall thickness
(mm)
S
Pipe serial
(-)
σs
Hoop stress
(N/mm2)
SDR
Standard Size Rate
da
External
Pipe
(mm)
diameter The minimum wall thickness according to that:
Hoop stress calculation depends on safety factor.
MRS: Minimum Required Strength
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2. HOOP STRESS
PE CLASS
MRS
STRESS σ
SAFETY
WALL
WEIGHT
(N/mm2)
(N/mm2)
FACTOR
THICKNESS s
(kg/m)
(C)
(mm)
PE 63
6.3
5.0
1.25
10.0
3.14
PE 80
8.0
6.3
1.25
8.1
2.62
PE 100
10.0
8.0
1.25
6.6
2.17
STABILITY PRESSURE
Pipes that are laid under the ground are exposed to loads other than earth load. Those are, as it is the case in sea discharge when pipes are laid straight into the sea, extra loads such as loads that ground water creates, although the pipes are laid under the ground. Apart from these, stability calculation must be done in projects that have overstress such as sleeve concrete made for filling the gap in pipes that engage by sleeve method or additional loads in vacuum pipes that have absorption function. Stability Pressure Calculation for PE Pipes
Pk
Critical Collapse Pressure
(bar)
Ec
Elasticity Module
(N/mm2)
Number
of
Transverse
(-)
Thermoplasts s
Wall Thickness
(mm)
rm
Average Pipe Radius
(mm)
3. Acceptable Stability Pressure Calculation for PE Pipes
Pk,zul
Acceptable
Critical
Collapse
(bar)
Pressure fr
Reduction Factor
(-)
s
Safety Factor
(-)
Stability Pressure Calculation for PE Pipes
σk
Stability Pressure
(N/mm2)
Pk
Critical Collapse Pressure
(bar)
rm
Average radius
(mm)
s
Wall thickness
(mm)
4.CALCULATING PIPE DIAMETER The determination of the pipe section; continuity balance is established if passage flow rate at the water passageway is constant.
Q=0.0036 . A . v Q : Amount of Load A : Pipe Section V : Flow Rate If the passage flow rate at the gas and vapour passageway is constant, continuity balance is established. And the formula below is used:
m=0.0036 . A . v . ρ
m ρ
: Passage flow rate : Density of the material carried
5. PRESSURE LOSSES
Calculating Separate Pressure Losses In order to calculate the high energy loss or pressure loss due to passage amount, flow rate and pressure decrease in HDPE pipes, the formulas below are used: a)Darc-Weisbach Formula di
: Internal Diameter of the Pipe (mm)
I : Length of the Pipe Line (mm) V : Average Fluid Flow Rate (m/s) p : Fluid Density (kg/m3) I : Coefficient of Friction (-) High energy loss stands for the elevation differences intended for the desired flow rate in the line. b)Colebrook-White Formula
Re : Reynold’s Number v : Kinematical Fluidity of Water k : Hydraulic Smoothness Value of Internal Pipe Surface When the previous formula is transformed;
V
: Flow Rate
Je
: Energy Line Centering Trend
Kb : Working Smoothness There are two smoothness values: · Plate smoothness is ‘k’ · Working smoothness is ‘kb’
g
: Gravitational Acceleration
: Kinematical Hardness d
: Pipe Diameter
6.PRESSURE IMPACT There may be a pressure impact while the valve or the pump is switched on and off. Thus,
a
Ps value:
: Spreading Speed of Press Wave (m/s)
vo
: Flow Rate of the Fluid (m/s)
p
: Fluid Density (kg/m3)
Ps value can be positive or negative in practice. Positive value is observed while the armatures are switched off and the pump is switched on. Ps negative value is observed while the pump is switched off or hydraulic property suddenly changes. Spreading speed of press wave is calculated by the formula below:
Em : Elasticity Module of the Fluid (Esu) p : Fluid Density (kg/m3) Er :Elasticity Module of the Pipe (N/m2) Dm: Pipe Mid-Diameter(m) e : Pipe Wall Thickness (m) Short-term changes in pressure and the effect of pressure impact do not cause harm in HDPE pipes. 7.DILATATION Elongation ratio dependent on heat variability must be taken into consideration while the HDPE pipes are laid. At high temperature, there will be an increase, and at low temperature there will be a decrease in the length of the pipe. There will be 0,18 mm increase or decrease in length of 1m. part of the PE pipe, for every ‘K’ amount of temperature change.
MATERIAL
FACTOR mm/m.K
HDPE
0.18
PP
0.15
PVDF
0.14
PB
0.12
PVC
0.07
GFK
0.02
Coefficient of elongation for various plastic materials table
For instance, in a line made of PE pipes, when there is an increase or decrease in pipe length depending on temperature, there will be a dislocation in the pipe line, not at the fixed point but at the turning point of the pipe. Let us assume that, for a 12m. pipe, normal working temperature Tv=20 0C, maximum working temperature T1=65 0C and minimum working temperature T2=10 0C. Thus, length changes depending on temperature are calculated as follows: Increase in length depending on temperature rise :
Decrease in length depending on temperature drop :
Ls d k
: Fixing Range (mm) : Pipe Outer Diameter(mm) : Factor (26 for HDPE, 30 for PP, 33.5 for PVC)
8. FLEXIBILITY Maximum bending radius for PE pipes:
R Dm
: Bending Radius(mm) : Average Radius(mm)
E
HDPE CLASS
HOOP STRESS N/mm2
PE 63
5
PE 80
6.3
PE 100
8
: Pipe Elasticity Module (N/mm2) : Stress (N/mm2)
The possibility of breaking is the critical point while calculating the bending diameter for thin-walled pipes. For thick-walled pipes, while calculating the bending diameter, stretching-shrinking limit is the critical point. The formula below is used while calculating the acceptable bending radius for thin-walled pipes:
rm s
: Average pipe radius (mm) : Wall thickness(mm)
The formula below is used while calculating the acceptable bending radius for thick-walled pipes:
ra
: Pipe external radius (mm)
Site Ma p
E
: Stretching-shrinking rate (%)
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