a Resumo A necessidade de aços microligados, resistentes aos ambientes agressivos encontrados nas jazidas de petróleo e gás, como no pré-sal que contem quantidades consideráveis de ácido sulfídrico (H 2 S) e dióxido de carbono (CO 2 ), requer que todos os setores envolvidos na cadeia produtiva da indústria petroleira conheçam os fatores que influenciam os processos de corrosão e falhas provocadas pelo hidrogênio em tubulações e peças fabricadas com aços microligados. Assim, através de uma coleção de publicações selecionadas e USP, foi elaborado este texto, o qual não pretende ser uma revisão bibliográfica completa, mas sim indicar os principais fatores científicos e tecnológicos que estão envolvidos nas falhas provocadas por hidrogênio na presença de H 2 S, particularmente, quando relacionadas ao fenômeno de trincamento induzido por hidrogênio (Hydrogen Induced Cracking-HIC). Por ser um fenômeno complexo que envolve várias etapas, o tema foi abordado em termos das variáveis ambientais e metalúrgicas. O HIC se inicia com o processo de corrosão do aço, assim é preciso considerar os fatores do meio corrosivo (presença de H 2 S). Além disso, é necessário conhecer as interações dos compostos presentes no meio corrosivo com a superfície do metal e como elas afetam a adsorção e a entrada de hidrogênio atômico no aço. As etapas seguintes são a difusão, aprisionamento do hidrogênio e trincamento do metal, as quais estão relacionadas diretamente com a composição química do aço e microestrutura, fatores que dependem fortemente da fabricação do aço. Pretende-se, com esta revisão, dar uma visão geral dos conhecimentos quanto às falhas provocadas por hidrogênio e quais são os próximos desafios no desenvolvimento de tubulações para transporte de derivados de petróleo e gás natural. Palavras-chave: Aços microligados; Sulfeto de hidrogênio; Corrosão; Trincamento induzido por hidrogênio. AbstractThe need for microalloyed steels resistant to harsh environments in oil and gas fields, such as pre-salt which contain considerable amounts of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ), requires that all sectors involved in petroleum industry know the factors that influence the processes of corrosion and failures by hydrogen in pipelines and components fabricated with microalloyed steels. This text was prepared from a collection of selected publications and research done at the Electrochemical Processes Laboratory of Metallurgical and Materials Engineering Department, Polytechnic School, São Paulo University. This document does not intend to be a complete or exhaustive review of the literature, but rather to address the main scientific and technological factors associated with failures by hydrogen in the presence of wet hydrogen sulfide (H 2 S), particularly, when related to the Hydrogen Induced Cracking (HIC) phenomenon. This complex phenomenon that involves several successive stages, HIC phenomena were discussed in terms of environmental and metallurgical variables. The HIC starts with the process of corrosion of steel, therefo...

High strength low alloy (HSLA) steels are used for the construction of pipelines for oil and natural gas transportation. For such applications pipelines must exhibit mechanical resistance and resistance to corrosion and hydrogen induced cracking (HIC). API 5L X65 steels are the main materials used for this purpose. However, for economic reasons, the use of steels of superior grades would be of interest. This work presents a comparative study of the corrosion and HIC resistances of an API 5L X65 and an API 5L X80 steel in deaerated solution A of NACE TM0284 standard. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization experiments were performed in non-sour and sour (H 2 S-saturated) media, and HIC resistance tests were carried out in the sour medium. Scanning electron microscopy (SEM) and optical microscopy (OM) characterizations of polished and corroded samples were also done. Electrochemical tests showed that the API 5L X80 steel is slightly more susceptible to surface corrosion, which can be probably linked to its higher inclusion content and smaller grain sizes, it was also susceptible to HIC. Mn and S-rich inclusions found in the crack path indicate that this microstructural feature may play a key role in crack propagation and HIC susceptibility

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Pitting corrosion resistance of two austenitic stainless steels, 18Cr8Ni (Type 304L or UNS S30403 stainless steel) and 17Cr6Mn5Ni, was evaluated in three electrolytic solutions containing a fixed concentration of 0.6M sodium chloride and different additions of sodium sulfate, 0.06M, 0.15M or 0.6M. Cyclic potentiodynamic polarization tests were performed on as-received samples and on specimens annealed at 1010°C, 1040°C, 1070°C or 1100°C. The best pitting corrosion resistance was presented by the 17Cr6Mn5Ni steel annealed at 1070°C or 1100°C, with lower delta ferrite contents, in the electrolyte with the highest sulfate concentration. It can be found that the addition of sodium sulfate inhibits pitting corrosion and has a better inhibitor effect in the high manganese steel.

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The paper compares Hydrogen Induced Cracking (HIC) resistance and Hydrogen Permeation (HP) results for two API X65 microalloyed steels, with different contents of Mn and Nb: one containing low Mn and high Nb (L-Mn) and the other, high Mn and low Nb (H-Mn). The main objective is to correlate the microstructural differences between these steels with hydrogen diffusion and trapping behavior and hydrogen-induced cracking resistance. Both steel plates were characterized with optical and scanning electron microscopy in their transverse sections, in relation to the rolling direction. HIC resistance tests were made in accordance with the NACE TM0284-11 standard; samples obtained from the transverse section were also submitted to Hydrogen Permeation tests, based on the ASTM G148-97 standard. NACE solution A saturated with H2S was used in the two procedures. Besides, Thermal Desorption Spectroscopy measurements were made, in order to show which steel trapped more hydrogen atoms, and carbides/carbonitrides volume fractions were estimated with ThermoCalc software. The L-Mn steel presents a homogeneous microstructure through the plate thickness, composed of refined ferrite and small pearlite islands. The H-Mn steel has a heterogeneous microstructure through the plate thickness, composed of ferrite and pearlite bands, and presents centerline segregation. Hydrogen permeation tests showed that, despite all the microstructural differences, the hydrogen effective diffusion coefficient (Deff) was almost the same for both steels – the Deff obtained for the L-Mn steel is slightly higher than for the H-Mn steel. Contrary to expectations, the L-Mn steel presented higher hydrogen subsurface concentration (C0) and number of trapping sites per unit volume (Nt) values. Thermal Desorption Spectroscopy analysis confirmed that the L-Mn steel traps more H atoms than the H-Mn one. These results, along with the similar Deff values, can be explained by the presence of nanoprecipitates of microalloying elements, which, according to ThermoCalc simulations, appear in higher volume fraction in the L-Mn steel. Finally, the HIC tests results showed that the L-Mn steel has a better performance in sour environments; this behaviour is related with its special microstructural features.

ResumoAços inoxidáveis supermartensíticos (AISM) surgiram em meados dos anos 1990, após algumas empresas petroleiras e centros de pesquisa empreenderem projetos para desenvolver aços inoxidáveis com boa resistência mecânica e resistência à corrosão. A força motriz destes projetos foi a procura de aços inoxidáveis alternativos para os aços duplex e superduplex na extração de reservas de petróleo "offshore", devido a seu alto custo e a problemas de produção naquela época. Os AISM são derivados dos aços martensíticos inoxidáveis convencionais, possuem menor teor de carbono, para permitir melhor soldabilidade e melhorar a resistência à corrosão, adição de níquel para evitar a presencia de ferrita delta (δ) e adição de Mo, que também aumenta a resistência à corrosão. Através de ensaios de polarização potenciodinâmica foi avaliada a resistência à corrosão de um AISM 13Cr-5Ni-2Mo, denominado neste trabalho como AIS_2Mo, para três diferentes ambientes, NaCl, NaCl+CO2 e NaCl+H2S (soluções desaeradas). O material foi recebido como chapas laminadas a quente, as quais foram normalizadas a 1.050°C (½ hora/ar) e posteriormente revenidas a 600°C (2 horas/óleo). O melhor desempenho foi observado no eletrólito contendo apenas NaCl, com potencial de pite ao redor de 40 mV (ECS); o ambiente mais agressivo foi a mistura NaCl+H2S, com potencial de pite ao redor de -300mV (ECS), a mistura NaCl+CO2 teve potencial de pite intermediário, com valor 60 mV (ECS) abaixo do eletrólito contendo só NaCl. Palavras-chave: Corrosão por pite; Aço inoxidável supermartensítico; NaCl; CO2; H2S. BEHAVIOR OF A SUPERMARTENSITIC STAINLESS STEEL 13Cr-5Ni-2Mo IN THEENVIRONMENTS: NaCl, NaCl+CO2 e NaCl+H2S Abstract Supermartensitic Stainless Steels (SMSS) appeared in the middle 90's, after some oil and gas industries together with research institutes started projects to develop stainless steels containing good corrosion and mechanical properties. The driving force for this project was the search for new stainless steels as alternative to duplex and superduplex stainless steels, used in offshore oil extraction which have high costs and production troubles. SMSS are derived from conventional martensitic stainless steels, containing lower carbon (<0,02%C) to allow better weldability and improve intergranular corrosion resistance (because decrease in the formation of Cr23C6 precipitates), nickel is added to avoid the delta ferrite phase and molybdenum also is added to improve the corrosion resistance. Through potenciodynamic polarization tests the corrosion resistance of a SMSS with 13Cr-5Ni-2Mo, called here AIS_2Mo, was evaluated in three different electrolytes: NaCl, NaCl+CO2 and NaCl+H2S (deaerated solutions). The material was received as hot rolled plates, which were austenitized at 1,050°C (0,5 hours and air quenching) followed by tempering at 600 °C (2 hours and oil quenching). The best performance was observed in the electrolyte containing only NaCl, showing pitting potential (Ep) around 40 mV (ECS), the most aggressive environment was the mix of NaCl+H2S ...

Pipelines produced from High Strength Low Alloy steels (HSLA) are a safe and cheap way to transport large quantities of petroleum and gas. HSLA steels offers mechanical and economic advantages. When HSLA steels are exposed to environments containing hydrogen sulphide (H2S), the steel can corrode and generate atomic hydrogen in the surface wich can diffuse and trapped, leading loss of mechanical properties and subsequent failures. The infrastructure to transport oil and gas represent a high cost investment, in adittion, they must be free from degradation processes that can causes severe health and environmental impacts. For this reason, the development of materials with high performance in aggressive environments is required. However, the relationship between microstructure and Hydrogen Induced Cracking can not be generalized, since the susceptibility to cracking depends of several factors, like number of trap sites, binding trap energy, microstructural distribution and trap sizes. In addition, the presence of regions of low ductility can result in easy cracks nucleation and propagation. This thesis contributed to the understanding of the mechanisms that lead to hydrogen embrittlement and hydrogen damage, showing the relationship between microstructure, corrosion rate, diffusion and cracking, I ncreasing the scientific knowledge about the standard tests actually used to evaluate the performance of microalloyed steels in sour environments.