PSI - Issue 22

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

225

7

Table 2 prediction of crack arrest toughness in the class Ⅰ area of the 2 nd WEGP (12MPa, wall thickness 18.4mm, 15 ℃ )

Crack arrest lengths at 95% probability

Calculating methods

No.

gas compositions

Predicted C V , J

C V / C V EPRG

Tarim gas

126 150 145 182 215 257 180 215

1.17 1.39 1.37 1.69 1.98 2.38 1.67 1.99

11

1

BTC

G3

6 7 4 3 1 4 3

Tarim gas

2

BTC, Leis mod.

G3

Tarim gas

3

BTC, 1.71 mod.

G3

Tarim gas

4

BTC, 1.43 mod.

G3

Table 3 prediction of crack arrest toughness in the class Ⅰ area of the 2 nd WEGP (10MPa, wall thickness 15.3mm, 15 ℃ )

Crack arrest lengths at 95% probability

Calculating methods

No.

gas compositions

Predicted C V , J

C V / C V EPRG

Tarim gas

119 142 133 169 203 243 170 203

1.10 1.31 1.23 1.56 1.87 2.25 1.58 1.88

8 6 6 5 3 2 5 3

1

BTC

G3

Tarim gas

2

BTC, Leis mod.

G3

Tarim gas

3

BTC, 1.71 mod.

G3

Tarim gas

4

BTC, 1.43 mod.

G3

As can be seen from table 2, table 3 data, using the correction coefficient of 1.43, the predicted crack arrest impact energy can meet the probability that the pipeline can be cracked in 3 pipe lenghts to ensure that it reaches 95%. For 12MPa conveying pressure, the 1.43 correction coefficient is adopted, the toughness requirement of steel pipe in class Ⅰ areas is the average minimum 220J, and the average minimum 255J is achieved by using 1.71 correction coefficient. Considering the safety reliability and economy of pipeline, the toughness requirement can be reduced as far as possible under the premise of ensuring reliable crack arrest of pipeline. Therefore, the economical and reasonable 1.43 correction coefficient is chosen. For 10MPa conveying pressure, 1.43 correction coefficient is also used, and the toughness requirement of steel pipe in class Ⅰ areas is the average minimum 200J. 3.8. Crack arrest toughness requirement at different areas Due to the increase of wall thickness in class Ⅱ , Ⅲ and Ⅳ areas, the conveying pressure is unchanged, that is, the design factor and hoop stress of pipeline are lower than that of class 1 areas. As a result, class Ⅱ ~ Ⅳ areas require less crack arrest toughness than in class Ⅰ area. The BTC method is used to compare and analyze the crack arrest toughness required at different class categories, and the results are shown in Figure 5. In the international X80 full-scale burst test, no impact energy is less than 140J in the case of crack arrest. Therefore, for the class Ⅱ ~ Ⅳ areas, the single minimum value of impact toughness is proposed to be 140J, and the average minimum value is 180J. For class Ⅱ areas, if the supply of steel pipe mean 180J, the standard deviation is less than 40J, at this time in 2 pipe lengths crack arrest (that is, unilateral propagation of less than 12 meters) of the crack arrest probability is 95%, in 3 pipe lengths of the crack arrest probability of 99% (that is, unilateral propagation of less than 18 meters).