hdpe pipe thickness calculations

7/30/2019 HDPE Pipe Thickness Calculations

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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 (-)

s Hoop stress (N/mm2)

SDR Standard Size Rate

da External Pipe

diameter

(mm)

The minimum wall thickness according to that:

Hoop stress calculation depends on safety factor.

MRS: Minimum Required Strength

HDPE Pipe-Polyethylene Water Pipes & Fittings


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2. HOOP STRESS

PE CLASS MRS

(N/mm2)

STRESS

(N/mm2)

SAFETY

FACTOR

(C)

WALL

THICKNESS s

(mm)

WEIGHT

(kg/m)

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 pipesare 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 inpipes 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

Pressure

(bar)

fr Reduction Factor (-)

s Safety Factor (-)

Stability Pressure Calculation for PE Pipes

k 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 LoadA : Pipe SectionV : Flow RateIf 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 .


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m : 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 : Reynolds Numberv : Kinematical Fluidity of Waterk : Hydraulic Smoothness Value of Internal Pipe Surface

When the previous formula is transformed;

V : Flow Rate g : Gravitational Acceleration

Je : Energy Line Centering Trend : Kinematical Hardness

Kb : Working Smoothness d : Pipe DiameterThere are two smoothness values:

Plate smoothness is k

Working smoothness is kb

6.PRESSURE IMPACT

There may be a pressure impact while the valve or the pump is switched on and off. Thus, Ps value:

a : 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:


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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 : Fixing Range (mm)d : Pipe Outer Diameter(mm)k : Factor (26 for HDPE, 30 for PP, 33.5 for PVC)

8. FLEXIBILITY

Maximum bending radius for PE pipes:

R : Bending Radius(mm) E : Pipe Elasticity Module (N/mm2)

Dm : Average Radius(mm) : Stress (N/mm2)

HDPE CLASS HOOP STRESS N/mm2

PE 63 5

PE 80 6.3

PE 100 8

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:


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rm : Average pipe radius (mm)

s : Wall thickness(mm)

The formula below is used while calculating the acceptable bending radius for thick-walled pipes:

ra : Pipe external radius (mm) E : Stretc hing-shrinking rate (%)

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hdpe pipe thickness calculations

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