GRP
is almost as strong as steel, so GRP pipes can be used for high pressure
water mains even when surge pressure can be expected as the result
of water hammer.
A example of the mechanical properties referred to laminates obtained
by the filament winding process with a winding angle of 55 degrees,
is:
Hydrostatic
properties
|
Property
|
Test
method
|
Pipe
[N/mm2]
|
|
Ultimate
hoop stress
|
ASTMD1599
|
215
|
|
Hydrostatic
design basis
|
ASTM
D2992 method B
|
135
|
|
Hydrostatic
design stress
|
ASTM
D2992 method B
|
67.5
|
Design
values
|
Property
|
Test
method
|
Pipe
[N/mm2]
|
Fitting
[N/mm2]
|
|
Allowable
axial tensile strength
|
ASTMD1599
|
22
|
21
|
|
Axial
Tensile modulus
|
ASTMD1599
|
12500
|
10500
|
|
Allowable
hoop tensile strength
|
ASTM
D2290
|
43
|
21
|
|
Hoop
tensile modulus
|
ASTM
D2290
|
25000
|
10500
|
Poisson's
ratio
| |
Hoop
/ axial
|
Axial
/ hoop
|
|
Poisson's
ratio
|
0,27
- 0,30
|
0,50-0,55
|
Other
physical properties
|
Property
|
Unit
|
Pipe
|
Fitting
|
|
Coeff.
of linear thermal exp.
|
1/°C
|
2,5
x 10 E-5
|
3,0
x 10 E-5
|
|
Specific
gravity
|
Kg/m3
|
1850
|
1650
|
|
Glass
ratio (by weight)
|
%
|
70
|
40
|
|
Glass
ratio (by volume)
|
%
|
50
|
35
|
Fatigue
and creep can be controlled by specifying the appropriate design limits.
Both, experience and proven testing methods are available to predict
the long term behavior of the pipe and to establish the appropriate
design limits. One of the most severe testing procedures is that according
to ASTM D 2992. This consists in submitting 18 pipe samples to different
pressures so that the failure of the samples will occur at different
times and a regression line can then be drawn.
The following graph shows the results on pipe made by filament winding.
The test duration is 10,000 hours and the value at 100 years can be
extrapolated from the test results.
The residual capacity of the pipe is about 50% of the initial value.
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