PSI - Issue 22

Yaorong Feng et al. / Procedia Structural Integrity 22 (2019) 219–228 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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along the pipeline, etc.), the international full-scale burst test database and the Battelle hyperbolic model and the GasDecom software systematically study the crack arrest toughness requirement of the 2 nd WEGP, consider the safety, reliability and economic feasibility of the pipeline, and put forward the requirement of the pipe crack arrest toughness of the 2 nd WEGP. The scope of application of several commonly used methods for predicting crack arrest toughness was given in the ISO 3183 " Petroleum and natural gas industries - Steel pipe for pipeline transportation systems". For the 2 nd WEGP, only the BTC method is fully applicable, and when the BTC prediction result is greater than 100J, the prediction results should be corrected. The comparison and analysis of full-scale burst test results and theoretical prediction results show that the BTC method is suitable for the prediction of crack arrest toughness of X80 steel pipe in the 2 nd WEGP. In the prediction of crack arrest toughness, the effects of natural gas components, especially heavy hydrocarbon content, on the long range propagation and crack arrest resistance of pipeline, the changes of pressure and temperature along the pipeline and the different crack arrest toughness required by the specific combination are considered. 3.2. gas compositions In order to simplify the calculation process, Tarim gas and Central Asian gas are calculated separately, because there are many natural gas sources in the 2 nd WEGP provided by Central Asia Group. To simplify the calculation, a more rigorous group of Central Asian gas compositions is simulated and recorded as G3 gas (see Table 1). G3 corresponds to more heavy hydrocarbon compositions, but the proportion is higher than that of natural gas.

Table 1 Different gas compositions used to calculate the fracture toughness of the 2 nd WEGP gas compositions C1 C2 C3 iC4 nC4 iC5 nC5 C6

CO 2 0.20 0.10 0.10

N 2

G1 gas G2 gas

92.14 92.14 92.00

3.55 4.35 4.50

1.40 1.00 1.50

0.40 0.30 0.40

0.40 0.30 0.40

0.20 0.10 0.20

0.20 0.10 0.20

0.11 0.11 0.20

1.40 1.41 0.50

G3 test gas

allowable range

92.00~ 92.60 96.23

3.00~ 4.50

0.40~ 1.50

0.12~ 0.40

0.10~ 0.40

0.05~ 0.20

0.05~ 0.20

0.05~ 0.20

0.10~ 2.00

0.50~ 2.00

Tarim gas

1.77 3.96 ≤ 6

0.30 0.34

0.06 0.12

0.08 0.09

0.02

0.02

0.05

0.47 1.89

0.97 0.84

Turkmenistan gas

92.55

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Central Asian gas spec.

>92

<3

<3

<3

<3

<3

<3

<2

<2

Note: Test gas compositions are for reference only.

3.3. Pressure-temperature combination along the compressor station

The pipeline conveying pressure and gas temperature between the gas stations in the 2 nd WEGP are gradually reduced, and the temperature decreases faster than the pressure. Pressure reduction and temperature reduction require just the opposite of crack arrest toughness. For different pressure-temperature combinations along the pipeline, the amount of crack arrest impact energy required is shown in Figure 2. From Figure 2, it can be seen that the outlet of the compressor station on the 2 nd WEGP has the highest temperature, but the highest pressure, and the maximum predicted impact energy for crack arrest. When the pipeline is shut down, the impact energy required by G1 and G2 is 127J and 123J respectively (11MPa-6 Celsius), which is also lower than that required by the exit.