The FeCl3 test is applied to an increasing extent for examining the resistance to pitting and crevice corrosion. Two methods having proved their value are described, the chemical properties of the FeCl3 solution with regard to hydrolysis, pH and redox potential behaviour at various test temperatures are set forth and finally numerous results of the application of this test to high‐alloy stainless steels and nickel alloys are presented. These results have been used to establish, be means of multiple regression, two empirical equations that allow to estimate rather accurately the critical pitting and crevice corrosion temperatures (CPT, CCT) from the contents of the decisive alloying constituents. These temperatures vary by about 2.5°C in the CPT test and by approx. 10°C in the CCT test, which can be reduced, however, by extending the test period beyond 24 hours. This is due to the fact that corrosion potentials in a 10% FeCl3 · 6H2O solution take a long time to stabilize. The variation of the critical crevice temperature can be further reduced by pressing the crevice blocks at a higher torque to the specimen. Another section particularly deals with the application of the CPT test for determining the influence of the matrix on the resistance to local corrosion. Consequently, the CPT test lends itself excellently to the examination of welds and as a quality control. Finally, CPT test results are compared with pitting data determined electro‐chemically in artificial seawater. This shows that the ranking order with regard to corrosion resistance is identical, although media and processes differ considerably from each other.
This article describes fatigue crack growth experiments to investigate the degradation of the durability of polymers due to fluid environments. The degrading effect of media causing stress cracking can be observed on the fracture surfaces of tested samples by scanning electron microscopy. Strategies to improve environmental stress cracking like changes in molecular weight, orientation, toughening with rubber particles of different sizes are discussed. Fatigue crack growth experiments can be employed as a very fast and effective screening method.
This paper presents new data on the resistance of recently developed high-alloy stainless steels to localised corrosion in chloride solutions. Pitting potential was determined in artificial sea water, and critical pitting temperature CPT in very aggressive F e Q solution. Critical crevice corrosion temperature CCT was tested in the same FeCl, solution. Stress corrosion measurements, made in a more familiar NaCl solution by the drop evaporation method, demonstrate that alloy stainless steels with high chromium and molybdenum have very long failure times, comparable with those of nickel alloys found to be SCC-resistant under practical conditions. Stainless steels of 20 Cr 25 Ni 6Mo type showed the best resistance to localised corrosion.Es werden neuere Ergebnisse iiber die Bestandigkeit der weiterentwickelten hochlegierten CrNiMo-Stahle gegeniiber Lokalkorrosion in stark chloridhaltigen waBrigen Medien vorgelegt. Es wurden die LochfraBpotentiale in kunstlichem Meerwasser sowie die kritischen LochfraR-und Spaltkorrosionstemperaturen in der aggressiven 10% FeC1,-Losung ermittelt. SpannungsriR-Korrosionspriifungen mittels auftropfender NaC1-Losung auf den erhitzten Werkstoff (Drop Evaporation Test) zeigen, daR sehr hoch in Chrom, Molybdan und Nickel legierte nichtrostende Stahle hohe Standzeiten aufweisen, die mit solchen Nickellegierungen vergleichbar sind, die sich in der Praxis als bestandig gegeniiber SpannungsriBkorrosion erwiesen haben. Der nichtrostende Stahl mit 20 Cr 25 Ni 6 Mo (1.4529) zeigt die beste Bestandigkeit gegeniiber allen Lokalkorrosionsarten.
Early stages of cyclic fatigue-loaded polystyrene (PS) specimens were investigated by positron annihilation lifetime spectroscopy (PALS) at a maximum stress amplitude of 15 MPa. PALS yields information about the average unoccupied hole volume. A linear increase in the ortho-positronium (o-Ps) lifetime was observed in a range from 0 to 50,000 cycles. This increase occurs homogeneously distributed at different positions along a sample of 170 mm. The average unoccupied void volume increases by 1.2%. On the other hand, the o-Ps intensity shows no systematic change upon cycling. The results suggest a homogeneous and linear increase in free volume prior to craze formation
Alloy 33 (UNS-R20033), a new corrosion-resistant austenitic material based on chromium (mass fraction of the elements, %: 33 Cr; 32 Fe; 31 Ni; 1.6 Mo; 0.6 Cu; 0.4 N), appeared on the market in 1995. In this paper, we present new data on its mechanical properties, formability, weldability, activation characteristics, and behavior under corrosion conditions. We have established that the mechanical properties of welded articles, including impact toughness, are a good match for the same properties of plates, allowing plastic deformation without fracture. When held for up to 8 h at a temperature from 600~ to 1000*C, the alloy is not activated in boiling azeotropic nitric acid (the Huey test). In tests under service conditions, alloy 33 displays exceptional corrosion resistance in 96-98% H2SO 4 at 135-140"C and in 99.1% H2SO 4 at 150"C. Alloy 33 also has rather successfully undergone testing in 96% H2SO 4 with nitrosyl impurities at 240"C. In nitric acid, alloy 33 is resistant at a concentration up to 85% at 75"C and even higher temperatures. The alloy also has corrosion resistance in 1 M HCI at 40"C and in NaOH/NaOCI solutions. In artificial sea water, the pitting potential remains unchanged at temperatures up to 75"C and also is much higher than the oxidation-reduction potential of sea water at 95"C.Alloy 33 is easily formed; articles of any required shape can be made from it. The new data confurm the generalpurpose nature of the ~alloy, which allows it to meet the diverse requirements of chemical technology, oil and gas, and oil refining industries.Alloy 33 was developed in the 1990's with the goal of obtaining exceptional corrosion resistance under conditions of a strongly oxidizing medium and overcoming problems arising in fabrication and welding of articles with large cross sections made from superferritic corrosion-resistant steels [1]. Furthermore, manufacturers of components of steels sometimes required material with higher structural stability for replacing the corrosion-resistant fractions with high molybdenum content. As a result, the described alloy was developed: a solid solution based on chromium, alloyed with nickel and nitrogen impurities for stabilization of the austenitic microstructure.The corrosion resistance of steel is enhanced as a result of adding molybdenum and copper impurities. As established in [2], the nominal pitting resistance equivalent (PRE) of the new steel is 50, which is higher than the PRE of 6% molybdenum austenitic corrosion-resistant steel and alloy 626 based on nickel. We should also note that, despite the presence of chromium and nitrogen, alloy 33 displays a high degree of thermal stability, which may be explained by the austenitic microstructure and balanced chemical composition.Weldability and Activation Behavior. As shown by the tests carried out according to ISO requirements, the impact toughness of alloy 33 is 280 J/m 2. After arc welding of a plate of thickness 15 mm with a tungsten electrode in a shielding gas medium (GTAW, Gas Tungsten Arc Welding) with the same mater...
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