Wyniki wyszukiwania - BazTech

1

The use of computed tomography and scanning microscopy methods for assessing the alkaline reactivity of aggregate

Zapała-Sławeta Justyna

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2024

|

Vol. 72, nr 3

art. no. e149814

EN

The reaction of alkalis with aggregate containing reactive forms of silica (ASR) plays a significant role in shaping the durability of concrete, as the strongly hygroscopic reaction products generated lead to internal stress, causing its expansion and cracking. This study presents an extended analysis of corrosive processes occurring in mortars with reactive natural aggregate from Poland, using computed tomography and scanning microscopy methods. Numerous cracks in the grains and the surrounding cementitious matrix were observed, indicating a high degree of advancement of corrosive processes. Over time, the proportion of pores with reduced sphericity increased, indicating ongoing degradation of the mortars. The usefulness of computed tomography in studying the progress of ASR was demonstrated. Scanning microscopy confirmed that the cause of mortar degradation is the formed ASR gel with a typical composition, located within the volume of reactive grains, cracks propagating into the cementitious matrix, and accumulated in air voids.

2

Mikrostruktura i właściwości mechaniczne stali bainitycznej Cr-Mo po eksploatacji

Golański Grzegorz, Kolan Cezary, Bruneè Krzysztof, Staszałek Kamil

Energetyka

|

2022

|

nr 3

155--157

PL

Badaniu poddano próbki pobrane z wycinka rury wykonanej ze stali bainitycznej P5 (X11CrMo5). Badany materiał pracował w temperaturze 534°C przez ponad 93 000 godzin. Po eksploatacji badana stal charakteryzowała się nadal zachowaną mikrostrukturą bainityczną z licznymi wydzieleniami. Wydzielenia typu M23C6 obserwowano na granicach ziaren byłego austenitu, na granicach listew bainitu, natomiast wewnątrz listew bainitu ujawniono obecność cząstek M2C i M23C6. Badana stal charakteryzowała się względnie niewielkim stopniem degradacji mikrostruktury i właściwościami wytrzymałościowymi wyższymi od wymagań normatywnych.

EN

The samples taken from the pipe section made of P5 bainitic steel (X11 CrMo5) were tested. The test material was operated at 534°C for over 93,000 hours. After operation, the tested steel was still characterized by bainitic microstructure with numerous precipitates. The M23C6 type precipitates were observed at the former austenite grain boundaries, at the boundaries of the bainite laths, while the M2C and M23C6 particles were revealed inside the bainite laths. The tested steel was characterized by a relatively low degree of microstructure degradation and strength properties higher than the standard requirements.

3

The mechanical properties and the microstructural degradation effect in an old low carbon steels after 100-years operating time

Lesiuk G., Szata M., Bocian M.

Archives of Civil and Mechanical Engineering

|

2015

|

Vol. 15, no. 4

786--797

EN

The paper presents the results of historical types of steel after over 100 years of operating. The object of interest were parts of steel structure of the hall historic 19th-century Main Railway Station in Wroclaw. The study has shown the presence of the microstructural degradation processes in puddled steel. In all the analysed steels (low carbon puddled steel) microstructure degradation processes were related to: presence of numerous precipitations of carbides and nitrides (or the carbides–nitrides) of iron inside the ferrite grains, presence of continuous precipitations of cementite at ferrite grain boundaries. In order to restore the initial state of the microstructure, all tests were carried out in two stages of heat treatment; as-received state and after the normalisation (950 °C, 2 h, cooled in air) state. The microstructures degradation significantly influenced the mechanical properties. Its influence is most strongly emphasized in the impact resistance test results. It has been shown that the presence of degradation processes significantly changes the type of fracture; from ductile to the cleavage. This fact is well illustrated by the SEM-images of crack path. Results of the fatigue crack growth rate test indicate for worsening of resistance to the fatigue crack propagation of the material depending on the degree of degradation processes intensity in tested steel. The differences in the kinetics of fatigue cracking are also well illustrated by the SEM-images along the fatigue crack path. The authors have proposed a new kinetic equation of the fatigue crack growth rate for puddled steel.

4

Mikroanaliza złączy spawanych nadstopów żelaza IN519 i H39WM po eksploatacji

Jasiński W., Zawada P., Kochmański P.

Inżynieria Materiałowa

|

2010

|

Vol. 31, nr 2

157-160

PL

Jedną z metod otrzymywania wodoru jest reforming parowy. Endotermiczny proces rozkładu mieszaniny metanu z parą wodną pod ciśnieniem do 4,0 MPa prowadzony jest w temperaturze do 780°C w odlewanych odśrodkowo austenitycznych rurach wypełnionych katalizatorem niklowym. W pracy przedstawiono wyniki badań mikroanalizy rentgenowskiej złączy spawanych odlewanych odśrodkowo rur katalitycznych ze stopu drugiej generacji IN 519 oraz stopu trzeciej generacji H39WM. Badania przeprowadzono na złączach spawanych doczołowo, pobranych z obszaru wlotu substratów o temperaturze pracy ok. 500°C oraz z obszaru maksymalnej prędkości pełzania rur. W warunkach pracy reformerów amoniaku temperatura ścianki zewnętrznej rur przy wylocie produktów zbliża się do 900°C. Efektem długotrwałej eksploatacji są zmiany fazowe i strukturalne zależne od lokalnej temperatury materiału rury. Zmiany te wpływają na właściwości mechaniczne materiału rur i przyczyniają się do inicjacji procesu pełzania, objawiającego się makroskopowo lokalnym powiększeniem średnicy rur. Krańcowym stadium procesu wysokotemperaturowej degradacji mikrostruktury są makropęknięcia doprowadzające do utraty szczelności rur.

EN

Steam reforming is one of the methods to produce hydrogen. The endothermic decomposition process of the mixture consisting of methane and water vapour under a pressure up to 4.0 MPa is conducted at a temperature up to 780°C in austenite iron based alloy pipes cast centrifugally and filled with nickel catalytic agent. The results of microstructure investigations of the welded joints of catalytic pipes cast centrifugally, made of the second generation alloy IN 519 and the third generation alloy H39WM were presented in the article. The microstructural tests were conducted on butt welds drawn from the area of the substrate inlet of a temperature approx. 500°C and from the area of maximum speed of pipe creep. The temperature of the pipe external wall at the outlet of the products approaches 900°C under the operation conditions of ammonia reformers. Long- lasting operation results in phase and structural changes depending on the local temperature of the pipe material. These changes affect the mechanical properties of the pipe material and contribute to initiation of creep process which manifests itself in macroscopic aspect as a local increase in the diameter of the pipes. The extreme stage of the high temperature degradation of the microstructure reveals as macrocracks leading to the loss of pipe leak-tightness.

5

Influence of sulphur on high temperature degradation of steel structures in the refinery industry

Hucińska J.

Advances in Materials Science

|

2006

|

Vol. 6, nr 1

16-25

EN

This paper reviews sulphidation behaviour of steel structures in the refinery industry. The data presented are related to two aspects of the corrosion. One aspect refers to external degradation of the structures due to formation of sulphide scales on the steel surface and metal losses; another is connected with internal degradation, i.e. changes of steel microstructure and formation of internal corrosion products. The so-called modified McConomy curves, and the Couper-Gorman curves used to predict corrosion rates of steels in hydrogen-free refinery streams, and hydrogen-containing environments are shown. Decreased stability of carbides in steel due to the presence of sulphur on the steel surface is considered, and a role of hydrogen in this process is outlined.

6

Analiza matematyczna sygnału ultradźwiękowego w ocenie degradacji mikrostruktury stali niskostopowej w instalacjach przemysłowych

Manaj W., Kurzydłowski K.J., Sieniawski J.

Mechanik

|

2005

|

R. 78, nr 5-6

502-505

7

Damage accumulation in cast steel reformer tubes.

Łabanowski J., Krzysztofowicz K.

Inżynieria Materiałowa

|

2001

|

R. XXII, nr 4

554-557

PL

Referat przedstawia wpływ czasu pracy rur katalitycznych wykonanych ze staliwa gatunku IN-519 (24%Cr, 24%Ni, Nb) na przemiany strukturalne przebiegające w wysokich temperaturach. Przedstawione zostały zależności właściwości mechanicznych i struktury rur po długotrwałej eksploatacji. Stwierdzono, że zmiany zachodzące w strukturze staliwa obserwowane na mikroskopie świetlnym nie zachodzą w sposób ciągły z czasem eksploatacji i nie mogą być podstawą do określenia stopnia degradacji materiału. Zmiany wydłużenia próbek wyznaczone w statycznych próbach rozciągania wykazały dobrą korelację z czasem pracy rur.

EN

The paper presents effects of long-term service at elevated temperatures on microstructural changes of catalytic tubes made of the alloy IN-519 (24%Cr, 24%Ni, Nb). The relationship between mechanical properties obtained in static tensile tests and the degree of microstructure degradation is discussed. It was found that structural changes observed with the use of light microscope occur in non-monotonic way with operating time at elevated temperatures, thus the tube's structure can not be consider as a measure of material's degradation after exploitation. Decrease of elongation values obtained in tensile test show the best correlation with the working time of reformer tubes.