PSI - Issue 60

M.K. Sahu et al. / Procedia Structural Integrity 60 (2024) 390–401 M. K. Sahu et.al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Geometries of pipe specimens and experimental failure loads corresponding to monotonic fracture tests.

Moment (kNm)

Load , (kN)

,

Inner Span, (mm)

Outer Span, 2500

Crack Size ( 2 ) * 64.88 o

Sl. No.

Experiment Name

Length (mm)

Crack location

(mm)

t (mm)

(mm)

8-QMSP-60 TWC-CSB-M1 12-QMSP-60 TWC-SSW-M2

1

219.0

18.6

880

2945

Base

450.25

182.4

Weld center

2

324.0

27.5

1300

3600

4000

61.54 o

714.42

410.8

Note: QMSP: Quasi Monotonic Straight Pipe; TWC: Through Wall circumferential Crack; CSB: Carbon Steel Base; SSW: Stainless Steel Weld * After fatigue pre-cracking The maximum experimental load ( , ) obtained by monotonic fracture test, is also shown in the table in the second-last column. This load is also shown in terms of capacity moment , of the pipe This capacity-load value , is an important loading parameter used for deciding the peak load of cyclic loadings further. 3.2. Monotonic fracture test results During both monotonic fracture tests different experimental results like total load applied, LLD and CMOD are recorded. One 8-inch pipe having through-wall crack, 8-QCSP-60-TWC- CSB-M1 and another 12-inch pipe 12 QMSP-60-TWC-SSW-M2 are tested under monotonic loading. Different experimental results like Load vs. LLD, Load vs. CMOD and Load vs. Crack growth are shown for both pipes in Fig. 1(d), Fig. 1(e) and Fig. 1(f) respectively. This test result is used as relevant base line data for the cyclic tearing tests on other through-wall cracked 8-inch pipes 8-QCSP-60-TWC- CSB-LC1, 8-QCSP-60-TWC- CSB-LC3, 8-QCSP-60-TWC- CSB-LC4, which were tested under cyclic loadings with different load values , . Here , is the peak load value of cyclic loading which is certain fraction (from 0.67 to 0.8) of the experimentally obtained maximum load, , values for CS and SSW pipes in these monotonic fracture tests. The load values , are 450.25 kN and 714.42 kN for CS pipe 8-QMSP 60-TWC-CSB-M1, and SS pipe 12-QMSP-60-TWC-SSW-M2 respectively as shown in Table 1. 3.3. Cyclic tearing testing All the cyclic tearing tests have been conducted under load-controlled mode four-point bending. The load was applied cyclically in a triangular waveform pattern. The load was applied at slow rates i.e., quasistatic manner. The specified load amplitude was kept constant throughout the test. The maximum loading level , for cyclic loading was calculated based on the maximum experimental load, , of identical pipe already predicted by monotonic fracture test, which are shown in Table 1. For all 8-inch pipes to tested under cyclic loadings, , are calculated based on , = 450.25kN for 8-inch pipe 8-QMSP-60-TWC-CSB-M1. Similarly for a 12-inch pipe tested under cyclic loading , is calculated based on , =714.42kN for the 12-inch pipe tested under monotonic loading, 12-QMSP-60-TWC-SSW-M2. Table 2 shows the test matrix where initial geometric parameters and loading value for this category are tabulated. It should be noted that maximum experimental load for 8-inch pipe = , 8 = 450.25kN, and for 12-inch pipe = , 12 =750.42kN. The applied maximum/peak load for cyclic loading, , is calculated using these maximum experimental load values and premeditated load reduction factor ( ), which is shown in the second last column of the Table 2. In the last column the total numbers of cycles ( ) endured by the pipes during the cyclic tearing tests are tabulated. This experimental work involves four cyclic fracture tests on fatigue pre-cracked straight pipes. Three tests are on seamless 8 -inch carbon steel pipes while the remaining one test is on a 12-inch similar metal conventional groove welded (SMW) pipe.