Issue 46

I. Čamagić et alii, Frattura ed Integrità Strutturale, 46 (2018) 371-382; DOI: 10.3221/IGF-ESIS.46.34 372 presence of the crack type error. Based on the research results, the analysis of the resistance to brittle fracture was performed in order to compare the obtained values for characteristic areas of welded joint and justify the selection of welding technology. K EYWORDS . Welded joint; Tensile properties; Plane strain fracture toughness; Critical crack length. and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION long-time exploitation period of a pressure vessel-reactor (over 40 years) has caused certain damages to the reactor mantle. The occurrence of these damages required a thorough inspection of the reactor construction itself, as well as the repair of damaged parts. Repairing of the reactor included the replacement of a part of the reactor mantle with newly built-in material. The given pressure vessel was made of low-alloyed Cr-Mo steel A-387 Gr. B in accordance with ASTM standard with (0.8-1.15)% Cr and (0.45-0.6)% Mo. For designed working parameters (p = 35 bar and t = 537  C) the material is in the area of tendency towards decarbonisation of the surface which is in contact with hydrogen. The surface decarbonisation may reduce the strength of the material. The reactor, based on its construction represents a vertical pressure vessel with a cylindrical mantle. Deep lids of the same quality as the reactor mantle are welded to upper and lower side of the mantle. The most important process in motor gasoline production stage takes place in the reactor- a platforming for altering the structure of hydrocarbon compounds and achieving a higher gasoline octane number. Testing of a new and exploited parent metal (PM), the weld metal-WM and heat affected zone (HAZ), included the determinating of tensile properties and fracture mechanics parameters of the new and exploited PM and welded joint components (WM and HAZ), at room and working temperature of 540  C, [1]. Welding technology qualification for sheets made of new and exploited PM was performed in accordance with standard SRPS EN ISO 15614-1, [2]. The research performed here was based on the experiences from previous experiments involving the determining of fracture toughness and fatigue crack growth parameters at room and working temperatures, as seen in [3,4]. M ATERIALS FOR TESTING oth exploited (E) and new (N) steel A-387 Gr. B with thickness of 102 mm were analyzed. Chemical composition and mechanical properties of the exploited and new PM according to the attest documentation are given in Tab. 1 and 2, [1]. Welding of steel sheets made of exploited and new PM was performed in two stages, according to the requirements given in the welding procedure provided by a welding specialist, and these stages include:  Root weld by E procedure, using a coated LINCOLN S1 19G electrode (AWS: E8018-B2), and  Filling by arc welding under powder protection (EPP), where wire denoted as LINCOLN LNS 150 and powder denoted as LINCOLN P230 were used as additional materials. Chemical composition of the coated electrode LINCOLN S1 19G, and the wire LINCOLN LNS 150 according to the attest documentation is given in Tab. 3, whereas their mechanical properties, also according to the attest documentation, are given in Tab. 4, [1]. Specimen mark % max. C Si Mn P S Cr Mo Cu E (Exploited) 0.15 0.31 0.56 0.007 0.006 0.89 0.47 0.027 N (new) 0.13 0.23 0.46 0.009 0.006 0.85 0.51 0.035 Table 1 : Chemical composition of exploited and new PM specimens. A B