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This study conducts a comparative electrochemical evaluation of three types of pearlitic steels used in flexible pipelines for oil transport in marine environments. The steels have been manufactured with chemical composition and geometry variations to optimize operation performance under adverse conditions. Electrochemical tests were conducted using solutions simulating marine environments with NaCl and CO2, and at high temperatures. The results indicated that spheroidized (SC) steel demonstrated the best corrosion resistance under these specific conditions. Additionally, the Raman spectroscopy characterization technique was used to analyze the layers of corrosion products formed during the tests, identifying the presence of FeCO3 (siderite) and other corrosive oxides. These discoveries are valuable for selecting and improving materials in flexible pipelines used in oil production in marine waters. The study highlights the importance of the cementite morphology present in pearlite as a relevant factor in the corrosive behavior of steels, contributing to the development of more efficient and durable solutions for the offshore oil and gas industry. [ABSTRACT FROM AUTHOR]

The dynamic transformation (DT) of austenite to ferrite and the retransformation of the dynamically transformed ferrite back into the more stable austenite were studied at temperatures above the Ae3. For this purpose, compression tests were carried out on a C-Mn and a Nb microalloyed steel over the temperature range 870-960 °C. The samples were deformed to a strain of 0.75 at a strain rate of 1 s−1 and held isothermally for times of 1-1000 s to permit retransformation. The samples were water quenched after testing and the volume fractions of retransformed ferrite were measured to allow for the construction of TTRT (time-temperature-reverse transformation) curves. The present type of diagram can be combined with strain-temperature-transformation (STT) curves to model the occurrence of dynamic transformation and retransformation during thermomechanical processing. [ABSTRACT FROM AUTHOR]

The dynamic transformation (DT) of austenite to ferrite and the retransformation of the dynamically transformed ferrite back into the more stable austenite were studied at temperatures above the Ae3. For this purpose, compression tests were carried out on a C-Mn and a Nb microalloyed steel over the temperature range 870-960 °C. The samples were deformed to a strain of 0.75 at a strain rate of 1 s−1 and held isothermally for times of 1-1000 s to permit retransformation. The samples were water quenched after testing and the volume fractions of retransformed ferrite were measured to allow for the construction of TTRT (time-temperature-reverse transformation) curves. The present type of diagram can be combined with strain-temperature-transformation (STT) curves to model the occurrence of dynamic transformation and retransformation during thermomechanical processing. [ABSTRACT FROM AUTHOR]

A five-pass rolling schedule is simulated by means of torsion testing. The first and last pass temperatures are 920 and 860 °C with 15° of cooling between passes. All of the rolling is carried out above the Ae3 temperature of 845 °C that applies to this steel. Interpass times of 10, 20, and 30 s are employed, which correspond to cooling rates of 1.5, 0.75, and 0.5 °C s−1, respectively. Samples were quenched before and after the first, third, and fifth passes in order to determine the amount of dynamic ferrite produced in a given pass. The data also allow for estimation of the amounts of ferrite that retransform to austenite during the time between passes. The volume fractions of ferrite and martensite (prior austenite) were determined by optical metallography. The amount of dynamic ferrite formed and retained increased with pass number. The volume fraction of ferrite that retransformed increased with pass number, averaging about 4, 6, and 9% for the 10, 20, and 30 s interpass times, respectively. The simulations indicate that ferrite is unavoidably produced during plate rolling and that the microstructure present at the initiation of accelerated cooling does not consist solely of austenite. [ABSTRACT FROM AUTHOR]