PSI - Issue 42

Tadeu Messias Donizete Borba et al. / Procedia Structural Integrity 42 (2022) 276–283 Tadeu Messias Donizete Borba / Structural Integrity Procedia 00 (2022) 000 – 000

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2.2. CTOD Results Tables 4 and 5 show the results of the CTOD test performed at -10 °C in specimens with a notch positioned on the Base Metal (BM) and Weld Metal (WM), respectively. All specimens, regardless of the region sampled by the notch, meet the fatigue precrack requirement, according to ISO-12135. The BM specimens presented excellent results, with CTOD values not less than 1.4 mm. As for the WM specimens, lower results were obtained, however, higher than 0.5 and 0.9 mm for the FCAW and SAW joints, respectively. It should be emphasized that the CTOD results performed on the WM are not necessary according to API RP 2Z standard and these results are presented in this work for information purposes only.

Table 4. CTOD results performed in seven specimens of the base metal (BM). Specimen ID CTOD (mm) BM1 1.83 BM2 1.43 BM3 1.55 BM4 1.53 BM5 2.04 BM6 2.72 BM7 2.52 Mean 1.95 ± 0.51

Table 5. CTOD results performed in three specimens of the weld metals (information purpose). FCAW Specimens CTOD (mm) SAW Specimens

CTOD (mm)

FW1 FW2 FW3 Mean

0.81 0.53 0.99

SW1 SW2 SW3 Mean

1.21 0.97 1.01

0.78 ± 0.23

1.06 ± 0.13

The CGHAZ CTOD results for the two welded joints, are given in the Table 6. It is verified that the specimens sampled in the FCAW joint presented lower values than the specimens sampled in the SAW joint. This fact was associated with higher sampling of the CGHAZ region by the notch in the FCAW joint compared to the SAW joint. Fig. 4 shows the CTOD results of the CGHAZ of the SAW joint (grey points) and the FCAW joint (red points) as a function of the sampled fraction of the CGHAZ by the notch. In general, regardless of the welding condition, a drop in fracture toughness values is observed proportionally to the increase in the amount of CGHAZ sampled, a region that presents deleterious microconstituents for this property, a fact that has been widely reported in literature (Alé, R,M. (1994), Davis, C.L. King, E.(1994), Lee, S. et al(1992),Shi, Y.W. (1997), Toyoda, M (1989), Vishnu, P.R. (1984), Yang, X. et al (2019), Zhang, J.X,). Also, for the FCAW joint, the deposition of a high number of passes, due to the use of a low heat input, provided the formation of a HAZ with a significant amount of intercritically reheated regions (ICCGHAZ) which, according to the literature (Alé, R,M. (1994), Davis, C.L. King, E.(1994), Lee, S. et al(1992),Shi, Y.W. (1997), Toyoda, M (1989), Vishnu, P.R. (1984), Yang, X. et al (2019), Zhang, J.X,), are deleterious to the toughness of the material because they present a significant amount of the MA (Martensite-Austenite) constituent. Therefore, the presence, along the notch of the FCAW joint, of high fractions of the regions CGHAZ and ICCGHAZ, which have low resistance to cleavage fracture and, therefore, can be considered as Local Brittle Zones (Fairchild, D.P. (1987)) was considered to be the main factors for their lower fracture toughness results. The API RP 2Z standard specifies a minimum CTOD value in the HAZ of 0.30 mm for steels with yield strengths up to 60 ksi (420 MPa). For steels with yield strength greater than 60 ksi, the case of API X80MO steel, the standard states that the criterion must be agreed between the manufacturer and the purchaser like in EN-10225. Besides, there are many other standards used in CTOD testing and evaluation for welded joints to evaluate the HAZ toughness of steel plates for pre-production evaluation of offshore structure steels. In this study, for the judgment of the CTOD result, it was used the standards DNV-OS-C401(2018), DNV-OS-F101(2012) Submarine Pipeline Systems, NDE (Book a MQPS 0-3 (2010)), API1104 (2005) or Petrobras standard N-1678 (2010) as a reference. In the case of the DNV-OS-C401, DNV-OS-F101 standard and NDE (Book a MQPS 0-3), CTOD results greater than or equal to 0.15