S. Lalik

Welding of Gas-Tight Pipe Walls Made of Composite Pipes of 3R12/4L7 Steel

The paper presents the results of macro and microstructure testing, hardness measurements and tensile test of submerged arc welded joints of composite pipes made of two grades of steel with X6CrNi18-10 steel flat bars intended for operation in elevated temperature. The outer part of the composite pipe is made of Sandvik 3R12 steel (grade ASME 304L/SA) and has austenitic microstructure, whereas the inner pipe – of Sandvik 4L7 steel (grade ASME SA-210A1) and has ferritic pearlitic microstructure. The results of the tests were used as a base to elaborate the Welding Procedure Specification allowing to obtain high quality joints with correct structure and high mechanical properties.

Testing of Welded Joints of Gas-Tight Pipe Walls Made of New Generation Martensitic Steel Type VM12-SHC

The paper presents the results of macro and microstructure testing and of hardness measurements of submerged arc welded joints of VM12SHC steel pipes (special high corrosion resistance, X12CrCoWVNbN12-2-2) with flat bars made of 10CrMo910 steel, intended for operation in elevated temperature. The tests were performed on welded joints that were not heat-treated and welded joints that were annealed (at 735-745°C for 0.5 hours) after welding. The results of the tests were used as a base to elaborate a Welding Procedure Specification.

Tests of Welded Joints of New Generation Austenitic, Stainless Steel HR3C

The paper presents the characteristics of a new generation of austenitic stainless HR3C also used on items of equipment operating at elevated temperatures. Changed welding technology and the results of metallographic and mechanical properties of joints. Developed and implemented welding technology made it possible to obtain high-quality connectors, the correct construction of the required structural and mechanical properties.

Welding Duplex Steel Type X2CrNiMoN25-7-4 with Analysis of Ferrite Content Measurements in Welded Joints

The paper presents tests results of mechanical properties, hardness measurements, microstructure and the content of ferrite with the use of ferrite meter (feritscope) FMP30 and quantitative metallography technique with the use of Met-Ilo program in welded joints of steel X2CrNiMoCuWN25-7-4 with the use of TIG method. On the basis of achieved results of tests it was concluded that the applied technology of welding was correct and the usefulness as well as limitations of both methods were proved in the assessment of ferrite and austenite content in welded joints from duplex steel.

Potentiodynamic Tests of Magnesium Alloy AZ31 with Lithium Additive

The purpose of the study is to assess electrochemical corrosion resistance of magnesium alloy AZ31 with additives of 4.5, 7.5 and 15 % lithium in NaCl solutions. Corrosion tests were performed in solutions with concentration 0.01 2 M NaCl with application of electrochemical testing system VoltaLab®PGP201. Resistance to electrochemical corrosion was evaluated on the ground of registered anodic polarisation curves by means of potentiodynamic method. Results of performed tests show unequivocally deterioration of corrosion characteristics of the alloy together with increase of molar concentration of NaCl solution. As chloride ions concentration increases, decrease of corrosion potential and polarisation resistance, as well as increase of corrosion current density are observed. Deterioration of corrosion characteristics of AZ31 alloy was shown with the increase of lithium content. It must be highlighted that irrespective of molar concentration of NaCl solution, there is also presence of pitting corrosion in the tested alloy. It proves that magnesium alloy AZ31-Li is not resistant to that type of corrosion. Test results prove that it is necessary to apply protective films on elements made of magnesium alloy with lithium additive.

Welding of Steel with High Manganese and Aluminum Content

The paper presents results of tests of mechanical properties, hardness measurements, macro-and microstructures of welded joints austenitic and austenitic-ferritic steel with high manganese and aluminium content meant for automotive industry. Tests were conducted on flat sheets made of steel X20MnAl18-3 and X55MnAl25-5. Tested welded joints were ruptured in tensile strength test in all cases inside the weld which is connected with lower resistance to stretching of welded joints in comparison with resistance of joined steels. Resistance to stretching of tested samples, regardless of the method of welding, is on a similar level.

Kinetics of Corrosion Processes of Alloy on the Intermetallic Phase Matrix FeAl in High Temperature in Air Atmosphere

The aim of this paper was to determine the resistance to high-temperature corrosion in atmosphere of air for alloy Fe-40Al-5Cr-0.2Ti-0.2B. Corrosion tests were conducted in temperatures from 600 to 900°C in time from 2 to 64 hours. Conducted tests have shown a slight increase of weight of samples in periods of time which followed. Increase of weight is connected with corrosion products in the form of passive oxides which form on the surface of the alloy. Kinetics of corrosion processes has parabolic course in tested temperature range which proves the formation of passive layers of corrosion products on the surface of samples. Heat resistance of the alloy on intermetallic phase matrix FeAl brings about potential possibilities to apply this alloy as a material meant for work in elevated and high temperatures in the environment which includes oxygen.

Mechanical properties of joints welded in creep-resistant low-alloy T24 steel

Because of the increasing efficiency of power units, it becomes possible to reduce fuel consumption during the generation of electric power and to limit harmful effects on the environment by lowering the level of impurities released to the atmosphere and thus, to also lower the cost of power genetration. A significant effect on the increased efficiency of power units has working at supercritical parameters. Traditionally, power units perform at subcritical parameters and their mean efficiency ranges from 33 to 36%. However, in supercritical conditions (400–850 power), the efficiency reaches 42–48%. Transfer to supercritical–parameter condition is effected by varying temperature of the feed water, pressure and the temperature of fresh and secondarysuperheated steam. In this context, it becomes necessary to design and use new grades of steel with better working propertries that would allow to reduce plate thickness and therefore, the mass of the boiler, and, consequently, bring about, as compared with the conventional steels, technical and economical improvements. The feed water temperature was raised to 290–300oC. The feed pipelines were made in 15NiCuMoNb5 steel intended for working at temperatures not exceeding 400 oC. Because of its strength properties and resistance to corrosion, this material is successfully used for this specified purpose and there is, therefore, no reason to search for any other steel grade. It was recognized that fundamental to further development of supercritical parameters of power units, were water-walls built of thin-walled tubing, the steam superand interstage heaters, thick-walled fresh steam pipelines and chambers. In the case of water-walls, it is important, when selecting steels, to ensure that, in addition to the strength and anticorrosive properties, the welding without the need for heat treatment is possible. Otherwise, because of the bulk of walls, it tends to be difficult. Postwelding hardness of the steel should not exceed 350 HV10. These requirements are fulfilled by T23 (HCM2S), and T24 (7CrMoVTiB 10-10) materials, for which the T22 (10CrMo9-10) steel (used in subcritical-condition power units) was the basis. In both steels (T23, and T 24), the content of carbon is reduced, and this, in turn, lowers their hardness, which is associated with the content of martensite in the steel structure to below 350 HV10. The increase in the resistance to creep of T23 steel was achieved by partial substitution of molybdenum by tungsten, and the addition of vanadium and niobium, and in T24 steel, by addition of vanadium, titanium, and boron. The HCM2S (T23) with the additions of tungsten, vanadium, and niobium was developed at Sumitomu (Japan), and 7CrMoVTiB10-10 (T24) steel in Europe at Vallurec & Mannesman. Typical chemical contents of these steels are given in table 1. The HCM2S (T23) steel definitely displays a better set of properties than the “fundamental” (2.25Cr – 1Mo) material. It has higher mechanical properties, resistance to creep, as well as higher heat resistance in the region of up to 600oC. The T23 and T24 steels contain less carbon than the 10CrMo9-10 material, and are therefore easier to use (welding, forming). Partial replacement of molybdenum by tungsten increases the resistance (to creep) of T23 steel by strengthening it. A similar effect is produced by vanadium and niobium due to precipitation of carbides. In T 24 steel, the increase in mechanical properties is achieved through the introduction of carbide-forming elements, such as vanadium, titanium and boron. The HCM2S and 7CrMoVTiB10-10 steels are used for small diameter and wall-thickness tubing. At the same time, investigations have shown that both steels can be used not only for boiler tubes, but that within the range of thick-walled, high-pressure pipelines at 500 to 550oC also provide a good alternative to the 99% martensitic, chromium steels. Benefits derived from the use of the new low-alloy ferritic steels are not confined only to the building of new installations working art super-critical Mechanical properties of joints welded in creep-resistant low-alloy T24 steel