|
Because pf perfect surface
elasticity coefficient ,sps pipes have the lowest affection from water impact
compared to the other pipe type for this reason for certain pipe lining project
,one size smaller sps pe 100 pipe can be used for the same work of the
alternative pipes .as it is seen from the table, for a velocity of 3 m/s , the
maximum internal pressure for sps pe 100 pipe is 14.03 bars but at the same
condition , the same pressure stand to be 21.63 bars for pvc pipes and 48.53
bars for steel pipes.
Advantage of
telescobic transport of pe pipes
Pe
pipes can be transported as the smaller diameter pipes are inserted into bigger
diameter pipes (telescobic transport) enabling big transport cost saving.
stowage of pe pipes
Advantage of making
turns using minimum number of elbows with pe pipe
Because
of their perfect elasticity ,sps pe 100 pipes can make turns with a radius of 20
– 35 times their outer diameter .while the other pipe types can make even 11 and
22 degree turns by using elbows .sps pe100 pipes can turn these angles without
any elbow or another fittings. This means big material and time saving in the
installation.
Sps
pe 100 pipe can even turn 90 degree without elbow with a turning radius which
will be calculated with the following formula.
R =
dd
(sdr -1)
1.12
r : the radius
with which the pipe can bend without breaking
dd
: outer diameter of the pipe
sdr : standard
dimension ratio (outer diameter / wall thickness)
(picture
showing bending ability of sps pipes.)
Advantage of minimum 50 years services life of pe pipes
The curve in the figure below
shown the change in the physical properties of pe 100 pipes time.
The production design of pe 100
pipes is done for a services life of 50 years so the minimum services life of pe
100 pipes is minimum 50 years.
Σ circumferecial stress
C=1/e(x10^3)
Design criteria
Classification of pe pipes
|
Mrs |
Class |
Nomenclature |
Design |
|
(mpa) |
No. |
Stress |
|
3.2 |
32 |
Pe 32 |
2.5 |
|
4 |
40 |
Pe 40 |
3.2 |
|
6.3 |
63 |
Pe 63 |
5 |
|
8 |
80 |
Pe 80 |
6.3 |
|
10 |
100 |
Pe 100 |
8 |
TOP
Design stress :
Σ = mrs
c
C : safety
coefficient (1.25)
(a picture
from welding application)
Calculation of wall thickness of pe pipes
The
following formula is used to used to calculated the force (n)
N = pdm
2
D : average diameter
P : internal pressure
N : force
Dm = d + d = d – s
2
The stress at the pipe surface
is calculated from the formula:
Σ =
pdm
2s
Wall thickness s
= pdm
2σ
Since the outer diameter is
consideration for pe pipes in international standard , formula
Dm = d + d = d – s
2
s= pd
2σ +p
Is obtained for calculating the
wall thickness
 external
hydrostatic pressure
TOP
In case of existence of
external hydrostatic pressure a load of pbdm
n = pbdm
2
Will be exerted on the pipe
.then the stress on the pipe due to the pressing on the pipe will be :
Σ
= pbdm
2
For the pipe under external
pressure , the torque also must be considered.
Σb
= e [ s ]
²
1-v² [dm]
The pressure that will create
the stress in formula above will be :
Pb
= 2e [ s ]
³
1-v² [dm]
Here ;
e
: elasticity module
v : poisson ratio
s : wall thickness
dm : average diameter
Water
impact
The change
of the velocity of the water passing from the pipe will create a pressure
fluctuation inside the pipe.
∆p = c ∆p / g
The
pressure change due to the change in the velocity of water will be;
∆p
- pressure change
G
- gravitational force (9.81 m/s²)
C
- velocity of the sound in water
∆v
- change in the velocity of water
The
pressure in case of
Hmax = his +∆p
The
pressure in case of depression;
For
calculating c value;
C = ___9900___
√ 48.3+k d/s
D - internal
diameter
S - wall
thickness
K - surface
elasticity co efficient
Pipe raw material surface elasticity
coefficients (k)
iron & steel
pipe 0.5
font
pipe 1.0
lead
pipe 5.0
concrete
pipe 4.4
pvc
pipe 33.3
pe 100
pipe 377
If we use another method for
calculating the water impact , the velocity of the sound in water is taken
as:
ep
g / γ
 c=
ep_
+ dm
ew
s
Here
Ew - elasticity
module of water
Ep - elasticity
module of pipe’s raw material
Y - density
of water
Dm - average
diameter
S - wall
thickness
For
pipes , ep
/ 1-v²
must be used for ep
value since ep / ew <<< dm / s
Ep
/ ew is neglected ,hence the formula above will turn to be ;
ep
g / γ - _s_
c=
1-v² dm
|
Velocities |
Pe 100 , dn 140,dint =
123.4 |
Pvc 100 , dn 140,dint =
123.4 |
Steel 5" dint =123.4 |
|
M/s |
C/g |
H max |
H work |
H min |
C/g |
H max |
H work |
H min |
C/g |
H max |
H work |
H min |
|
|
13.42 |
|
|
|
38.77 |
|
|
|
128.48 |
|
|
|
|
1 |
|
11.34 |
10 |
8.65 |
|
13.88 |
10 |
6.12 |
|
22.84 |
10 |
-2.84 |
|
2 |
|
12.68 |
10 |
7.31 |
|
17.75 |
10 |
2.24 |
|
35.84 |
10 |
-15.69 |
|
3 |
|
14.03 |
10 |
5.74 |
|
21.63 |
10 |
-1.63 |
|
48.53 |
10 |
-28.53 |
Case
of passage of from aside
The stress (ð)
and unit elongation (€) forming due to the passage of pipe from aside and
support the pipe as in figure above will be as follow
Ð
= σ
i²
= €
i²
16e d 16 d
And
Q = 6πe(d^4
– d ^4)
ð
i^4
Here,
ð
- collapse
e
- elasticity module
d
- outer diameter
D - internal
diameter
i
- interval of support
€
- unit elongation
q
- distributed load
Technical
specifications
Specification of sps
hdpe pe -100:
The list of specification are valid for the
pipes and fittings made of pe 100 raw material which are designed for use in
potable water and irrigation etc. Purpose.
§
All of the pe 100 pipes
fulfill the requirements of en -12201 standard and the design stress is 8 n/mm².
§
All of the test are
done according to en standards.
§
The pipe is in the
color of blue or black which is accepted internationally as drinking water pipe
colors. If required the pipe can be produced also in black color with blue
strips and for increasing the resistance of the pipe to direct sun light ,uv
protection.
§
Into the granule form
raw material it is not added any additive for production of the pipe and
fittings .raw material is used absolutely in its original composition.
§
The sps hdpe pe 100
pipes have perfect resistance to chemical solutions.
Repair
of damage pe pipe
The pipe can be damage in any case .the repair
of the pipe can be done using several method .it is necessary to choose the
best of these repair method which suits to the type of damage part on the pipe.
Making repair using
flange
The damage area of the pipe is unearthed to an
extend where the pipe can be moved towards each side.
The equipment necessary to make a flange
connection to pe pipe end are the following;
·
Butt welding machine
·
2 piece flange
·
Gasket for flange
·
Screw and bolts for
flange
·
Electric power supply.
TOP
Minimum required
strength (MRS)
Polyethylene pipes and fittings material are
evaluated by their minimum required strength (mrs)
When mdpe (pe80) pipes are
hydrostatically tested at 20 °c,
a minimum required strength at 50 years of 8mpa (80 dan/cm²
)- mrs)
When hdpe (pe100) pipes are
hydrostatically tested at 20 °c,
a minimum required strength at 50 years of 10 mpa (100 dan / cm²
) - mrs100.
Design
stress
The design stress for mdpe (pe 80) pipes
is 5mpa
The design stress for "hi strength " hdpe
(pe100) pipes is 8 mpa. The following table shows the comparison between the
50 years mrs values for mdpe (pe80) and hppe (pe100) pipes.
A new high performance hdpe (pe 100)
polyethylene pipe material for use in underground potable
Water mains. The new material's higher
permissible design strength (pe 100)- 8mpa:pe80 – 5mpa), together with its
superior toughness, allows the design engineer to use hdpe (pe 100)
pipes at substantially higher operating pressures than mdpe (pe 80)
pipes with equivalent sdr rating.
The enhanced performance allows hdpe (pe
100) pipes to be produced with thinner pipe walls than mdpe (pe 80) pipes of
equivalent sdr rating.
In addition to their superior qualities,
hdpe (pe 100) also has greater resistance to rapid crack propagation.
Standard dimension
ratio (SDR)
In polyethylene pipes of
25 mm nominal size and above, the pipe wall thickness bears a constant ratio to
the outside diameter, for a given pressure rating. This is known as the standard
dimension ratio (sdr), which is calculated as follows:
Nominal outside diameter /minimum wall
thickness = sdr e.g. The sdr of a 90 mm, 10 bar rated mdpe (pe 80) pipe 90 /
8.2=sdr11. The sdr of a 90 mm, 10 bar rated, hdpe (pe100) pipe is:-
90/5.1 =
sdr 17.6
Pressure rating
The pressure rating of polyethylene pipes is
generally referred to in 'bar', where 1 bar equals 10.2m head (approx).
Table 1 gives the pressure rating and sdr of both mdpe (pe 80) and hdpe (pe
100) pipes.
|
Nominal
Size
Mm |
Medium density (pe 80) |
High performance (pe
100) |
|
Sdr |
Max. Rated working
pressure |
Sdr |
Max. Rated working
pressure |
|
20 |
Sdr 9
|
12 bar |
- |
- |
|
25-63 |
Sdr 11 |
12 bar |
- |
- |
|
90-180 |
Sdr 11
Sdr 17.6 |
12 bar
7.5 bar |
Sdr 11
Sdr 17.6 |
16 bar
10 bar |
|
250-1000 |
Sdr 11
Sdr 17.6 |
10 bar
6 bar |
Sdr 11
Sdr 17.6 |
16bar
10bar |
sdr and maximum
rated working pressures
|
Pn(10 - 12.5) sdr (17 - 13.6) elbow 90
° |
|
Od |
Z |
R |
S |
I |
|
110 |
95.00 |
55.0 |
8.10 |
40 |
|
125 |
102.50 |
62.5 |
9.20 |
40 |
|
140 |
120.00 |
70.0 |
10.30 |
50 |
|
160 |
130.00 |
80.0 |
9.50 |
50 |
|
180 |
140.00 |
90.0 |
10.70 |
50 |
|
200 |
150.00 |
100.0 |
11.90 |
50 |
|
225 |
162.50 |
112.5 |
13.40 |
50 |
|
250 |
508.00 |
375.0 |
11.04 |
200 |
|
280 |
545.00 |
420.0 |
11.86 |
200 |
|
315 |
688.00 |
472.5 |
17.57 |
300 |
|
355 |
737.00 |
532.5 |
22.35 |
300 |
|
400 |
792.00 |
600.0 |
28.25 |
300 |
|
450 |
854.00 |
675.0 |
35.80 |
300 |
|
500 |
916.00 |
750.0 |
44.10 |
300 |
|
Pn(10 - 12.5) sdr (17 - 13.6) elbow 45
° |
|
Od |
Z |
R |
S |
I |
|
110 |
-- |
55 |
8.1 |
40 |
|
125 |
-- |
62.5 |
9.2 |
40 |
|
140 |
-- |
70 |
10.3 |
50 |
|
160 |
-- |
80 |
9.5 |
50 |
|
180 |
-- |
90 |
10.7 |
50 |
|
200 |
-- |
100 |
11.9 |
50 |
|
225 |
-- |
12.5 |
13.4 |
50 |
|
250 |
|
375.0 |
11.04 |
200 |
|
280 |
|
420 |
13.86 |
200 |
|
315 |
|
472.5 |
17.57 |
300 |
|
355 |
|
532.5 |
22.35 |
300 |
|
400 |
|
600.0 |
28.25 |
300 |
|
450 |
|
675.0 |
35.80 |
300 |
|
500 |
|
750.0 |
44.10 |
300 |
| 
