The high-strength quenched and tempered steels in high stressed structures allow significant reduction of the plate thickness, and thus lighter structures. Such steels easily meet customer high strength requirements with satisfactory toughness, even at temperatures down to –60°C. Due to lack of supported complete design codes, and modest experience, these steels require further investigation. This paper outlines the results of standard tests of elastic-plastic fracture mechanics parameters, e.g. crack growth resistance curves, J-a, CTOD-a, as well as evaluation of critical material properties, JIc, CTODIc, and elastic fracture mechanics parameter KIc, for both, base and weld metal. Ključne reči • poboljšani čelici povišene čvrstoće • parametri elasto-plastične mehanike loma • zavareni spojevi • S690QL, S890QL

Penstocks for hydro-power plants are mostly fabricated as pressure water steel pipelines. In addition, there are a several approaches for mechanical design and further installation practice, as well for quality insurance activities. While American standards fully cover all related activities (ASCE M79, AWWA M11, AWWA C206), there is luck of specific and consolidated support in European regulation. It seems that major welding quality insurance activities are covered by EN 12732 (which is a standard for gas supply systems) and by EN 10224 for base material (for steel water tubes). In addition, it seems that some major European companies, involved in penstock design and manufacture have been developed their own practices and regulations. Particularly, for designers it is of special concern, how to define appropriate methods and amount of non-destructive testing, especially while considering long (over 5km) and large diameter penstocks (over 2,5m), as well as relatively high working pressures (over 10barg). For such design condition, and in accordance to EN 12732, it is a quite reasonable to widen and straighten non-destructive testing, but consequently fabricators are facing significant fabrication costs. Therefore, this paper should outline some basic approaches and comparison of welding quality insurance, related to design and manufacture of welded steel penstocks, as well as suggestion for methods and amount of non-destructive testing related to design inputs.

Uses of lighter, stronger, reliable and cheaper welded steel structures are constant trends. There is a various industrial application where structural steels with higher strength replace conventional low strength structural steels. This paper will outline basic comparison of three type of structural steel selection influence on total welding fabrication costs of atmospheric oil storage steel tanks (design and fabrication according to API 650). However, there are a number of parameters which may influence welding fabrication costs, as well as different company’s experiences, and therefore provided calculation assumptions in this paper do not have any intention to underestimate them. While considering typical types of structural steels, i.e. S235, S275 and S355 (acc. to EN 10025) the basic parameters which influence its selection on total welding fabrication costs are described. In particular, paper will outline selection influence related to size of oil storage tank. In addition, only one particular type of tank shall be evaluated, i.e. oil storage tank with fixed roof within its size limits applicable for oil industry. While considering minimum required thickness of shell structure as defined in API 650 according to selected structural steel, and almost non-affected thickness of roof and bottom, the main influencing parameter, i.e. sizes of tank shell butt weld joints shall be evaluated. In all cases, the same possibly applied welding technology shall be considered, while considering appropriate filler material strength class. Finally, range of total welding fabrication costs savings due to the use of stronger structural steel shall be outlined in relation to oil storage steel tank size, as well as used spreadsheet calculation.

Under the influence of temperature and stresses, the heat resistant materials react by creeping. Boiler components subjected to creep have a limited lifetime. Creep and material structure evolution are tightly related and according to this rule a number of studies have been performed in order to relate micro structural investigation and service exposure or residual life. The determination of the structural conditions and the materials exhaustion of creep exposed power plant boiler components is increasingly carried out by field of metallography. For assessment of damage and of the risk associated with failure it is necessary to know the potential mechanisms of degradation and the rate of accumulation of damage. VGB-TW 507 represents guideline for the assessment of microstructure and damage development of creep exposed materials for pipes and boiler components.

This paper describes influences of heat input on leg size of pulsed GMAW fillet welds of unalloyed steel with thicknesses of 4 mm, in horizontal and overhead position. Varied parameters were welding current and speed, while voltage and current profile were predefined by welding equipment manufacturer. Influence is described through models based on linear regression analysis. Comparison is made between developed models, as well as with those available in literature.