Corrosão sob tensão de aço inoxidável austenítico soldado em ambiente evaporativo de gotejamento de água do mar sintética: ensaios estáticos

Abstract:

Pressure vessels, piping, heat exchangers and stainless steel equipment for use on offshore oil extraction platforms operate at temperatures up to 120 ºC and are subject to stress corrosion cracking in chloride containing environments, mainly exposed to sea water. In general, these components involve processes of union by arc-welding, presenting microstructural alteration and residual tension, due to the heat input. Stress corrosion cracking susceptibility tests were conducted under the drop of synthetic sea water in welded joints of UNS S31603 austenitic stainless steel at temperatures of 70 ºC, 90 ºC and 110 ºC and tensile stresses of 70 %, 90 % and 110 % of the material’s calculated yield strength. The tests employed four point bending devices for 500 h and dripping of synthetic sea water in the center of the test specimen, with a frequency of 10 drops/min. The results showed that the cracking mechanism involves localized corrosion and nucleation of cracks at the bottom of pits. For all tensile stresses studied, at a temperature of 70 ºC, the presence of crack nucleation was identified, with a depth of nearly 140 μm. All specimens tested with a temperature of 90 ºC showed cracking with depth of around 5 mm. In the temperature of 110 ºC, it was observed the presence of cracks with greater depth, in some cases causing the fracture of the specimen. It was observed that the formation of a salt deposit was fundamental for the crack nucleation, especially at the higher temperatures. The welded region did not exhibited a relevant role in the nucleation of the stress corrosion cracks on these experiments.


Reference:
PEREIRA, Henrique Boschetti; MOREIRA, Marcelo Ferreira; ALMEIDA, Neusvaldo Lira de; MIRANDA, Hélio C.; BAPTISTA, Ilson Palmieri. Corrosão sob tensão de aço inoxidável austenítico soldado em ambiente evaporativo de gotejamento de água do mar sintética: ensaios estáticos. In: INTERNATIONAL CORROSION MEETING, INTERCORR, 7., 2018, Fortaleza. Proceedings… São Paulo: ABRACO, 2018. 12 p.  

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