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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1.2. CTOD test According to API RP 2Z, the assessment of HAZ toughness were carried out by CTOD and Charpy impact test in two regions, close to the fusion line (FL), in the CGHAZ, and at the end of the HAZ, between the BM and subcritical region of the HAZ (SCHAZ). In this study, only the CTOD results obtained in the CGHAZ of welded joints of API X80MO steel will be presented, as it is the most complex test and because this is the region that has the worst toughness along a weld joint. All CTOD tests were performed as described in the ISO-12135(2021). To perform the CTOD test, SENB specimen type were used, with a width equal to twice the thickness, and the length four times the width, as described in the ISO – 12135(2021). The notch was positioned on the straight side of the groove along the thickness and made by Wire Cut Electrical Machining (EDM). Mechanical stress relief was also performed by lateral compression, as described in the ISO 15653 – C2 (2010), BS 7448 Part 2 (1997) and STP-995 (1988). According to the API RP 2Z standard, for the welded joint with the lowest heat input, it is necessary to obtain six valid specimens for the CGHAZ regions. For the joint with the highest heat input three valid specimens must be obtained in the CGHAZ region. In addition, CTOD tests were also performed in BM and WM (informat ive mean). All CTOD tests were performed at -10 °C. The requirements for validating the notch positioning, the fatigue pre-crack front shape, and the interpretation of the CTOD test results were performed according to the procedures described in API RP 2Z and ISO-15653 standards. According to the API RP 2Z standard, as a validation criterion, for both weld joints, the through-thickness notch can be placed normal to the plate surface and intersecting the HAZ for at least 75% of the notch length over the cent ral 2/3 of the specimen thickness. For CGHAZ, more than 15% of the notch length should be placed in coarse grain regions. Fig. 1 is a schematic summary diagram of the experimental procedure sequence.

Fig. 1. Schematic summary diagram of the experimental procedure.

2. Results and discussion 2.1. Macrostructures

Before the stage of making the specimens, all welded joints were subjected to ultrasound inspection, to assess their internal integrity. It was not detected, in any of the joints, discontinuities that could affect the analyses that were planned in this study. The macroscopic aspect of the gas flux cored arc welded joint and submerged arc welded joint can be seen in Fig. 2 and 3, respectively. It was found that the weld beads were free from discontinuities such as lack of penetration, porosity, excessive reinforcement, undercutting or slag inclusion that proving that the welding procedures used were appropriate for the manufacture of adequate joints for weldability assessment of API X80MO steel under low and high heat input conditions.