PSI - Issue 68

Nedeljko Vukojević et al. / Procedia Structural Integrity 68 (2025) 379– 385 N. Vukojević et al. / Structural Integrity Procedia 00 (2025) 000–000

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The carbon equivalent for the selected samples is given in Tab. 1. As in all three cases, materials with good weldability were used, and welding technology EN ISO 4063 - 121 (EPP / UP) was used to join the sheets, Tab. 2. 2.2. Technology of plastic processing Vessel heads for experimental research are made by gradual pressing from initial circular welded sheets. During such a process of making vessel heads, pressure zones are observed along the radius as a consequence of the manufacturing technology with a combination of welding and plastic deformation. The incremental deformation of the roundel is performed on a hydraulic press P2MF 200x4 type – Sertom, Milan, Fig. 1. with an exchangeable tool and pressure force.

a

b

Fig. 1. Production of vessel heads by the process of incremental sheet forming: (a) Roundel pressing; (b) Final shaping.

The goal of the experimental analysis, according to which the number of factors, the experimental domain, the method of forming the test execution matrix plan, and the specific type of analysis is determined, is to obtain a mathematical statistical regression model that will describe the objective function in a valid way. For the observed process, an experimental design of a four-factor process based on a partial multi-factor orthogonal plan of the first order (semi-replicate) type 2 4-1 is used. It is considered that there is no priori information about the significance of factor interactions.

Table 2. Welding procedure Additional and auxiliary material

Preheating temperature

³ 100 0 C

ESAB Ok Auto rod 13.40

200 0 C

Name and manufacturer

Interlayer temperature

Classification Type of lining

EN14171-A-S3Ni1Mo

PWHT Work

930 ± 40°C Manual

÷

14 mm/2 for t = 6 mm 15 ÷ 17 mm/2 for t = 10 mm 22 ÷ 24 mm/2 for t = 14 mm Grinding and brushing

Max. pass width / layer number

Wire diameter

Æ 3.0 mm

Drying Powder Remark

2h/350°C

Cleaning

OK-Flux 10.62

Other things

÷

Standard: EN14171-A

Several output values are set as objective functions. Tab. 3 shows the number and type of treated parameters in the experimental design. A matrix plan for performing experimental tests was defined (see Tab. 4). As observed parameters (Yi-j), the values of the total impact energy and fracture toughness measured in the heat affected zone (HAZ) of the butt-welded joint were used. Experimental tests were carried out on samples before and after post wielding heat treatment (PWHT), as required by the matrix plan. Thermal treatment of normalizing annealing is performed by heating up to 930 ± 40°C in a 5-hour period, holding at the reached temperature for about 0,5 hours and cooling in air. A part of the vessel head with a welded joint in the middle was taken for testing. The samples were taken from the outer cylindrical part of the heads and from the location where the plastic deformations were most intense. To determine the properties in the HAZ, after plastic deformation, test specimens were taken from the direction transverse to the longitudinal axis of the welded joint.