Karakterizacija prevlake 316L nanete postupkom plazma navarivanja

Parts of industrial machines and structures are often exposed to the action of aggressive environments, which in a short period of time can provoke the loss of their integrity. It is well known that for extending the service life against erosion and corrosion, protection of the exposed structure zone by coating is frequently used. Various application methods of protective coatings are applied, and the most common are welding and thermal spraying processes. The aim of this study was characterization of coatings made of stainless steel 316L, widely used in chemical and petrochemical industries. The coating was applied on a structural steel S235JR by plasma transferred arc using powder as a filler material. Due to a number of advantages, the plasma transferred arc (PTA) surfacing process has found significant usages in the field of surface protection. This paper presents results of hardness measurements in characteristic zones of the coating and the base material, as well as microstructural characterization of coatings using optical and scanning electron microscopy. Results of EDS analysis of the coating and hardness measurements indicated that a relatively high dilution (26.1 %) of the base material (BM) and the filler material (FM) occurred in a very narrow zone above the fusion line, and thus did not significantly affect the chemical composition of the rest of the coating. Also, erosion resistance tests of coatings were performed by changing the basic functional parameters that is the impact angle and the speed of erodent particles. It was observed that the erosion resistance of the coating material decreases approximately linearly with the increase of the particle speed. Also, with the increase of the impact angle of the erodent (up to 45 °), the mass loss of the coating material is increased.Delovi mašina i konstrukcija su tokom rada izloženi delovanju agresivne radne sredine koja u kratkom vremenskom periodu može da naruši njihov integritet. U zavisnosti od radnih uslova, površina materijala može da bude izložena raznim mehanizmima oštećenja, od kojih se izdvajaju eroziona i koroziona oštećenja. Produžetak radnog veka ugroženih zona mašinskih konstrukcija moguće je izvesti različitim postupcima nanošenja zaštitnih prevlaka, a najčešće su to različiti postupci navarivanja i metalizacije. Cilj ovog rada je karakterizacija prevlake izrađene od nerđajućeg čelika klase 316L, koja je našla široku primenu u hemijskoj i petrohemijskoj industriji, nanete plazma postupkom navarivanja korišćenjem dodatnog materijala u obliku praha, na konstrukcioni čelik S235JR. U radu je izvršeno merenje tvrdoće u karakterističnim zonama prevlake i osnovnog materijala, kao i mikrostrukturna karakterizacija prevlake na optičkom i skenirajućem elektronskom mikroskopu. Takođe, izvršeno je eroziono ispitivanje prevlake promenom parametara ispitivanja, pre svega ugla nastrujavanja i brzine čestica erodenta

Sudden changes in fluvial style across the Permian / Triassic boundary in the eastern Iberian Ranges, Spain: Analysis of possible causes

The sedimentary record of the Late Permian and Early Triassic of the eastern Iberian Ranges shows four major, sudden, or very rapid, vertical changes in fluvial style. The Late Permian sedimentary cycle starts with the Boniches Formation, of alluvial fan-braided fluvial origin, which grades vertically over within a few metres into the Alcotas Formation, deposited by low to high sinuosity, avulsion-prone rivers with extensive floodplains. The Alcotas Formation contains calcimorphic soils, plant remains and pollen and spore assemblages. However, the upper third of the unit is devoid of all organic remains and soils and is characterized by a dominant red colour, the sandstone levels were deposited by high-sinuosity, meandering rivers. This major change took place during the Late Permian and is probably coeval with the emplacement of the Emeishan basaltic Large Igneous Province (LIP) in SE China. Rocks of the Boniches and Alcotas Formations are separated by an angular unconformity from the overlying strata, which consist of the Late Permian conglomeratic Hoz del Gallo Formation, of alluvial fan–gravel braided fluvial origin and the sandy Cañizar Formation, of low-sinuosity sandy river origin. The Permian– Triassic boundary lies, probably between the upper part of the Hoz del Gallo Formation and the first metres of the Cañizar Formation. Late Permian pollen and spore assemblages have been found in the Hoz del Gallo Formation but the Cañizar Formation is barren, with the exception of an Anisian (Middle Triassic) assemblage at the top. Tectonic extensional pulses in the Iberian Basin caused the changes observed between the lower and upper parts of the Boniches Formation, at the base of the Hoz del Gallo Formation and between the lower and upper part of this Formation. The changes observed in the uppermost part of the Alcotas Formation are not easily explained by tectonic causes, nor those in the passage from the Hoz del Gallo Formation to the Cañizar Formation. Similar sedimentary characteristics of the sandy Cañizar Formation such as amalgamated sandstone bodies, erosion and reactivation surfaces, dominant trough cross-stratification, tabular geometry, absence of plant remains and pollen and spores, and absence of silts and clays to those of coeval formations in places as far away as Australia, South Africa and Brazil suggest a global rather than local cause for these abrupt changes in fluvial style. This global cause was probably die-off of plant cover over extensive areas of the catchment, related to the end of the Permian mass extinction and possibly related to the emplacement of the West Siberian basaltic Large Igneous Province (LIP), responsible for drastic atmospheric and marine changes

Effect of Baffle Cut and Baffle Spacing on Pressure Drop in Shell and Tube Heat Exchanger with U Tubes

A general procedure for heat exchanger design has been presented in the Heat Exchanger Design Handbook (HEDH) [1], but no precise criterion for determining baffle cut nor baffle  spacing has been offered, and the emphasis is only on heat exchanger's permissible range of application. In this paper, an optimization program has been used to calculate pressure drop, fluid velocity, heat power, overall heat transfer coefficient and middle temperature difference for various baffle cut and baffle spacing for the same type of heat exchanger, using the procedure in HEDH. This could be considered as complementary to the HEDH recommendations and can be used by designers and, generally, engineers for determining the right baffle cut and baffle spacing for their specific cases

Characterization of Tube Repair Weld in Thermal Power Plant Made of a 12% Cr Tempered Martensite Ferritic Steel

The heat resistant tempered martensite ferritic steel X20CrMoV121 (DIN) has been extensively used within the last few decades as a material for boiler tubing systems and pipelines in thermal power plants (TPP). Long-term behavior of this steel is vastly researched and very well known, but main disadvantage is its poor weldability. In situ welding of martensitic steels is always challenging task and is usually quite difficult to implement properly in a short time, during forced outages of TPP. In this paper, characterization and mechanical properties of undermatch welded joint made during partial replacement of boiler outlet superheater (SH) in TPP by austenitic filler material, after 10 years of service are presented. Due to cold technique of welding, which does not required post weld heat treatment, this procedure were regular and widely used repair welding technique in two TPP (620 MW) units. In the purpose of comparison, two other type of matching welding joints of the same SH were also characterized: shop welded joint made by electrical resistance flash butt welding, as well as field welded joint made by gas tungsten arc welding during assembling of SH, which were both in service approximately 150,000 h.Lecture Notes in Mechanical Engineering, International Conference on Fatigue and Fracture at All Scales (NT2F), Sep 15-18, 2014, Belgrade, Serbi