The document discusses the design of an aramid fiber reinforced pipe. It is designed to have a minimum 20 year lifespan operating at maximum allowable operating pressure (MAOP) and withstand hydrostatic testing up to 1.25x MAOP for 8 hours up to 3 times without degrading the 20 year design life. The pipe strength comes solely from the aramid fiber reinforcement, while the plastic layers provide a barrier but no strength. Various design considerations, such as fiber selection and long-term strength behavior, are discussed.

1. Robert Gleim
Oct. 27th, 2010

2.  Pipe is designed to handle the following load
conditions:
◦ A minimum design life of 20 years at MAOP and
MAOT
◦ Hydro testing to 1.25x MAOP for 8 hours at MAOT
 The Hydro test can be performed up to 3 times during
the life of the pipe without degrading the 20 year
design life
 Pipe shall have a minimum design life of 1 week when
continuously operated at 1.25x MAOP
 The pipe design strength is based only on the
aramid fiber.
◦ No strength is attributed to the plastic.

3.  Base Tube
◦ Plastic is a seal and permeation
barrier layer only
 No strength is attributed to the
plastic.
◦ Multi-Layer or Single Layer
 Tri-axial aramid fiber
◦ Provides the strength to maintain
both axial and radial loads
◦ Maximum efficiency of braid
 Jacket
◦ Used to protect the aramid fiber
from damage during handling and
installation
 No strength is attributed to the
plastic.
 Couplings
◦ Provide connections between pipe
lengths and retains aramid fiber to
prevent slippage.

4.  Fluid Compatibility  Liner Material:
◦ Nylon Inert to
◦ HDPE Hydrocarbons
 Water only  Doesn’t Soften and Swell
◦ Nylon  Doesn’t Lose Strength
 Inert to Wet CO2
 Water with  Not for H2S over 200PPM
Hydrocarbons & CO2 ◦ PPS
◦ PPS  High H2S environments
 Water with  Jacket Material
Hydrocarbons, CO2, & ◦ Nylon for pipe pulls
H2S  Good abrasion resistance
◦ Polypropylene or nylon
for direct bury

5.  Tri-axial fiber reinforcement
◦ Axial fibers sized to carry 100% of axial load and to
maintain elongation at less then 1%.
◦ Radial fibers sized to carry 100% of radial load
 Braid angle optimized to minimize braid consumption and
maximize production lengths
Neutral
Braid
Angle =
54.7°

6.  Graphite/Carbon fiber
◦ High strength & good
resistance to cyclic loading
◦ Too expensive
 Aramid fiber
◦ Very similar properties to
carbon fiber
◦ Good balance of cost and
performance
 S- Glass fiber
◦ Low cost, high initial
strength
◦ Reduced strength in moist
environments due to crack
growth
◦ Poor cyclic performance

7.  It is necessary to understand the long term behavior of
aramids under load.
◦ Strength of the fiber is influenced by load, time and temperature
◦ Product life increases with decreased temperature and load

8.  It is necessary to understand the long term behavior of
aramids under load.
◦ Aramid fiber will retain its full strength for more than 80% of its
predicted time to failure.
◦ Time to failure is determined by Miners Rule:

9.  See attached chart for example below.
 At 90°F, the pipe must meet the criteria of 20 year
design life and Hydro testing at 1.25x MAOP.
◦ At MAOP, the load in the fiber is only 53.2 % of the short
term breaking strength (B.S.). This yields a design life
maximum of 50 years.
◦ A 1.25x MAOP hydro test, increases the aramid fiber load
to 66.5% of B.S. with a max design life of 1 week.
 If three - 8 hour, 1.25x hydro tests are performed on the pipe
during its life, approximately 14.2% of the pipe life is consumed
during the 24 hours of testing (24 out of 168 hr design life)
 The remaining pipe design life is approximately 34
years
◦ (85.8% of 50 years x 80% of predicted life at full strength)

10. Long Term Breaking Load of Aramid Fiber in PolyFlow
100
90
1 Week Life @ 1.25 x MAOP
80
66.5% 90°F
70
180°F
Static Load % of BS at 20°C
60 125°F
1.25x
50
53.2 % Design Load @
40 Approximately a
50 Year Design
Life
30
20
10
0
0.0001 0.001 0.01 0.1 1 10
Design life in Years

11. • A Factor of Safety (FS) is the structural capacity beyond the
anticipated applied load.
• A FS is used to provide a design margin over the theoretical design
capacity to allow for uncertainty in the design process.
• The uncertainty could be any one of a number of the components of the
design process including calculations, material strengths, manufacture
quality, environmental conditions, duty, etc.
 Accounting for Uncertainties:
◦ Design uncertainties:
 2D vs 3D effects & braid efficiencies accounted for by burst testing samples
at operating temperature, thus FS=1
◦ Manufacturing uncertainties:
 Braid pitch, angle, diameter and wall thickness variations accounted for by
burst testing samples at operating temperature, thus FS=1
◦ Material uncertainties:
 Braid: varies for temp and design life, typically between FS=2.03 to FS =2.81
◦ Operating uncertainties:
 Variability in installation, bend radii, operating pressure & temp, thus FS=1.1
Minimum Factor of Safety for Gathering lines is greater than 2.2