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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2. Crack initiation toughness and brittle fracture control of the 2 nd WEGP

2.1 Toughness requirement for preventing crack initiation in welded areas

Referring to ASME standard, assuming that there are surface crack defects with depth of t/4 in pipeline, using Level 2A evaluation curve and Failure Assessment Diagram recommended in BS 7910 "Guide to methods for assessing the acceptability of flaws in metallic structures", the 2 nd WEGP is analyzed and calculated (calculation parameters are adopted the design values of class Ⅰ areas of the pipeline, steel grade X80 the outside diameter of steel pipe is 1 219 mm, the wall thickness is 18.4 mm at pressure of 12 MPa and 15.3 mm at pressure of 10 MPa). The results are shown in Fig.1.

0 10 20 30 40 50 60 70 80

CVN(J)

0

200

400

600

800 1000 1200

Defect length （ mm ） Fig. 1 Weld initiation toughness requirement 缺陷长度2C(mm)

When the Charpy V-notch impact energy is 60J, the defect initiates when the length exceeds 150 mm, and when the Charpy impact energy is 70J, the defect of any length does not initiate. Therefore, considering that the length of defects in the welding area is less than 150 mm, the welding area can be prevented from cracking. That is to say, the single minimum Charpy impact energy of weld seam and heat-affected zone free from cracking can be determined to be 60J. The impact toughness requirement for preventing cracking in welds and heat affected zone of buried pipeline of the 2 nd WEGP are as follows: impact energy, minimum 60J for a single sample, average minimum 80J for 3 samples; test temperature is - 10 ℃ . 2.2 DWTT toughness requirement for steel pipe free from brittle fracture In order to ensure that the pipeline does not occur brittle fracture, the pipe material should have a sufficiently low ductile to brittle transition temperature. The shear area of DWTT has become the main control index to prevent the brittle fracture of pipeline. For the 2 nd WEGP buried pipeline requirement: the average minimum value of the fracture shear area of the transverse specimen of the pipe body 85%, a single minimum value of 70%; The test temperature is 0 ℃ . 3. Prediction of crack arrest toughness requirement of the 2 nd WEGP 3.1. Prediction methodology Based on the analysis and research of the main factors affecting the crack arrest toughness of the pipeline (pipeline geometry parameters, conveying pressure, natural gas compositions, pressure and temperature distribution