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Research Papers: Materials and Fabrication

Effects of Loading Mode on Brittle Fracture of X70 Pipe Girth Welds

[+] Author and Article Information
Dong-Yeob Park

CanmetMATERIALS,
Natural Resources Canada,
3303—33 Street N.W.,
Calgary, AB T2L 2A7, Canada
e-mail: dong-yeob.park@canada.ca

Jean-Philippe Gravel

CanmetMATERIALS,
Natural Resources Canada,
3303—33 Street N.W.,
Calgary, AB T2L 2A7, Canada
e-mail: jean-philippe.gravel@canada.ca

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 16, 2016; final manuscript received November 8, 2016; published online February 3, 2017. Assoc. Editor: Kunio Hasegawa.

J. Pressure Vessel Technol 139(3), 031403 (Feb 03, 2017) (6 pages) Paper No: PVT-16-1138; doi: 10.1115/1.4035272 History: Received August 16, 2016; Revised November 08, 2016

A series of single-edge notched tension (SENT or SE(T)) and single-edge notched bend (SENB or SE(B)) testing was carried out at −15 °C using B × B specimens machined from two API X70 large diameter pipeline girth welds. An initial notch was placed either on the heat-affected zone (HAZ) or the weld metal center from the outer diameter side of pipe to simulate a circumferential surface flaw. SE(T) and SE(B) tests were performed according to the CANMET procedure and ASTM E1820, respectively. For all HAZ SE(B) specimens machined from one pipe, ductile cracks initially propagated away from the fusion line and toward the base metal side due to asymmetric deformation, and then pop-in (i.e., the initiation and arrest of a brittle crack) occurred after ductile crack growth of approximately 1 mm, where the crack reached around the intercritical heat-affected zone. HAZ SE(T) specimens also showed that the ductile crack propagation deviated toward the base metal side, but an unstable brittle crack extension was not observed from any SE(T) specimens as opposed to SE(B) specimens. None of the weld metal SE(T) and SE(B) specimens showed pop-in or brittle fracture at −15 °C or room temperature. The difference in test results, for the same material, is associated with the different constraint levels in the two loading modes, taking into account that pop-ins were triggered in high-constraint SE(B) tests, while it was not the case for low-constraint SE(T) tests.

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References

Figures

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Fig. 1

Low-temperature SE(T) setup with hydraulic grips inside an environmental chamber

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Fig. 2

J-resistance curves obtained at −15 °C: (a) 17.8-mm and (b) 13.4-mm thick pipes for SE(B). SC and DC denote shallow (a/W ∼ 0.3) and deep cracks (a/W ∼ 0.5), respectively. Symbols are raw data, and solid lines are curve-fits. The coefficients of determination, R2, of the curve-fits presented in the figures are more than 98%.

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Fig. 3

J-resistance curves obtained at −15 °C: (a) 17.8-mm and (b) 13.4-mm thick pipes for SE(T)—single clip gauge. SC denotes shallow (a/W ∼ 0.35). The coefficients of determination, R2, of the curve-fits presented in the figures are more than 98%.

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Fig. 4

CTOD-resistance curves obtained at −15 °C from single- and double-clip-gauge SE(T) methods for HAZ specimens of 13.4-mm thick pipes (a/W ∼ 0.35)

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Fig. 5

J-resistance curves obtained from the room temperature testing of HAZ specimens from the 17.8-mm thick pipe for (a) SE(B) and (b) SE(T). SC and DC denote shallow (a/W ∼ 0.3) and deep cracks (a/W ∼ 0.5), respectively. The coefficients of determination, R2, of the curve-fits presented in the figures are more than 98%.

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Fig. 6

Load-CMOD curves of HAZ SE(B) specimens machined from the 17.8-mm thick pipe showing pop-ins (a/W = 0.5)

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Fig. 7

Fracture surface and cross section of a SE(B) specimen notched in HAZ region with pop-in occurred, 17.8-mm thick pipe: (a) crack plane and (b) a cross section at the dotted line in figure (a)

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Fig. 8

Fracture surface and cross section of a SE(T) specimen notched in HAZ region, 17.8-mm thick pipe: (a) crack plane and (b) a cross section in the middle of the crack plane of figure (a)

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Fig. 9

Comparison of measured and unloading-compliance predicted crack size for (a) SE(B) and (b) SE(T) specimens tested at −15 °C

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