Effects of CO2 impurities on the consequences of pipeline releases – possibility of fracture - presentation by Alexander Collard in the Effects of Impurities on CO2 Properties session at the UKCCSRC Cardiff Biannual Meeting, 10-11 September 2014

1. Effects of CO2 impurities on the consequences of pipeline releases – possibility of fracture
Alexander Collard
Drs Solomon Brown, Sergey Martynov, Garfield Denton and Peng Zhang
Supervisor: Professor Haroun Mahgerefteh
University College London

2. Outflow from CO2 pipelines
•
Possible outflow scenarios:
•
Accidental puncture (by far the most common)
•
Accidental Full Bore Rupture (FBR)
•
Controlled venting
•
Based on hydrocarbon pipeline experience – accidental punctures a matter of when, not if
•
Punctures can escalate to long running fractures, especially if they remain undetected
2

3. Pipeline fracture
•
Two types – ductile and brittle, both can be started due to external force
•
Ductile fracture characterised by:
•
Low crack tip velocity
•
Large deformation of the pipeline
•
Brittle fracture characterised by:
•
Pipe wall must cool to below its Ductile to Brittle Transition Temperature (DBTT)
•
Little deformation during fracture growth
•
Very rapid crack tip velocity
•
Fractures increase puncture to FBR and relocate release point
3

4. Blowdown on the CO2 phase diagram
4
1.0
10.0
100.0
150
170
190
210
230
250
270
290
310
330
Pressure (bar)
Temperature (K)
Triple Point
Critical Point
Solid
Liquid
Vapour

5. Ductile fracture modelling
•
Modelling software integrated:
•
Pipeline outflow model based on solution of the conservation equations for fluid flow – PipeTech
•
Dynamic boundary ductile fracture model based on Battelle Two Curve method
•
Composite model successfully validated against published experimental data
5

6. Pipeline simulation parameters for ductile fracture work
Parameter
Value
Length (m)
500
Internal Diameter (mm)
590.5
Wall thickness (mm)
9.45
Line pressure (bara)
100
Feed temperature (°C)
0, 10, 20, 30
Pipe wall/ambient air heat transfer coefficient (W/m2K)
5
Tensile stress (MPa)
531
Yield stress (MPa)
448
Pipe wall roughness (mm)
0.05
Pipe grade
X65
Fracture toughness (J)
50
Failure type
FBR at end 6

7. Pipeline inventory % composition for ductile fracture work
Species
Post combustion
Pre combustion
Oxy-fuel
CO2
99.82
95.6
88.4
Ar
-
-
3.7
CO
-
0.4
-
N2
0.17
0.6
2.8
H2S
-
3.4
-
Cl
-
-
0.14
H2
-
-
-
O2
0.01
-
3.6
SO2
-
-
1.36
H2O
-
-
-
NO2
-
-
-
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8. 0501001502002503003500100200300400500Crack Length (m) Crack Velocity (m/s) Curve ACurve BCurve CCurve D
Crack tip velocity vs. crack length for pure CO2 tests
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0 °C
10 and 20 °C
30 °C

9. 020406080100120-40-2002040Crack Tip Temperature (oC) Crack Tip Pressure (bara) Curve ACurve BCurve CCurve D
Variation of crack tip pressure and temperature
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30 °C
20 °C
10 °C
0 °C
Crack arrest pressure
Saturation curve
Liquid
Gas

10. Summary of all ductile fracture results
Composition
Temperature (°C)
Ratio of crack to pipeline length
Pure CO2
0
0.012
10
0.024
20
0.026
30
1
Post combustion
0
0.0012
(0.18 mole % impurities)
10
0.02
20
0.028
30
1
Pre combustion
0
0.012
(4.4 mole % impurities)
10
0.022
20
1
30
1
Oxy-fuel
0
1
(11.6 mole % impurities)
10
1
20
1
30
1
10

11. Brittle fracture modelling
•
Modelling software integrated:
•
Pipeline outflow model based on solution of the conservation equations for fluid flow – PipeTech
•
Rigorous brittle fracture model combining Finite Element and Weight Function methods to calculate Stress Intensity Factor (SIF)
•
Accounts for real pipe/puncture geometries, crack geometry, hoop stresses and material toughness
•
SIF used as characteristic criterion for low temperature induced brittle fracture
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12. Pipeline simulation parameters for brittle fracture work
Parameter
Value
Length (km)
10
Outer diameter (mm)
609.6
Wall thickness (mm)
14.7
Line pressure (bara)
150
Feed and ambient temperature (°K)
283.15
External ambient
Air and buried
Pipe grade
British Gas LX/1
Pipe wall thermal conductivity (W/m.K)
53.65
Pipe wall heat capacity (J/kg.K)
434
Pipe wall roughness (mm)
0.05
DBTT (°K)
263.15
Fracture toughness above/below DBTT (MPa/m0.5)
95/40 12

13. Defect parameters for brittle fracture work
Parameter
Value
Failure mode
Puncture
Puncture diameter (mm)
20
Initial crack length (mm)
20
13

14. Variation of pipe wall temperatures for buried pipeline
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15. Variation of crack length with time
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16. Pipeline inventory % composition for brittle fracture work
Species
Post combustion
Pre combustion
5% N2
10% N2
CO2
99.82
95.6
95
90
Ar
-
-
-
-
CO
-
0.4
-
-
N2
0.17
0.6
5
10
H2S
-
3.4
-
-
Cl
-
-
-
-
H2
-
-
-
-
O2
0.01
-
-
-
SO2
-
-
-
-
H2O
-
-
-
-
NO2
-
-
-
-
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17. Variation of pipe wall temperatures at 10,000s
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18. Conclusions
•
Fracture models used in both studies relatively simplistic
•
Ductile fractures – impurities do affect fracture length, relationship is complicated by other factors such as temperature
•
Brittle fractures – impurities predicted to have no significant effect on the length of brittle fractures
•
Sufficient evidence to warrant further study (currently under investigation as part of EU FP7 project CO2QUEST)
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19. Selected References
•
Bilio M, Brown S, Fairwheather M, Mahgerefteh H. CO2 pipelines material and safety considerations. IChemE Symposium Series: HAZARDS XXI Process Safety and Environmental Protection, 2009.
•
Mahgerefteh H, Brown S, Denton G. Modelling the impact of stream impurities on ductile fractures in CO2 pipelines. Chemical Engineering Science. 2012; 74, 200-210.
•
Zhang P. Modelling brittle fracture propagation in the next generation of CO2 pipelines. University College London. PhD Thesis, 2014.
•
http://www.pipetechsoftware.com/
•
http://www.co2quest.eu/
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