One of the most important oil discoveries of the last 10 years, in the wholeworld, was made in Brazilian offshore deep waters. The so called BrazilianPre-salt province comprises reservoirs below a layer of variable thickness ofsalt, which can reach up to 2,000m. Since 2006 several oil fields werediscovered in this province and the initial evaluation shows that the oilreserves of the fields evaluated so far may, in the future, double the currentBrazilian proven oil reserves. Among the technological challenges that are being faced to put these hugereserves into production, an important one is the material selection forcorrosive environments. High pressures coupled to variable CO2 contents makethe use of carbon steel in wells, risers and topsides pipings nearlyimpossible, requiring extensive use of Corrosion Resistant Alloys (CRAs). This paper describes the work that was done to optimize the material selectionfor the initial pre-salt production development projects. This includes effortsto simulate the corrosive environment in wells, which are subjected toextremely high pressures and variable concentrations of CO2. Interactionbetween fatigue and corrosion in deep water risers and the materialsrequirements for the topside of floating production units had also to be takeninto account, as well as materials to withstand extremely low temperatures thatmay occur in the piping of the CO2 compression plant for injection in thereservoir, due to situations of depressurization (one important assumption inthe pre-salt development is not to vent the CO2 produced with the associatedgas. This CO2 will be reinjected in the reservoir, improving the oil recoveryor disposed in aquifers close to the producing reservoirs). In parallel with the materials selection process, a great effort is beingcarried out on research and development, aiming to optimize and improve thematerials used in the production systems. The most important lines of researchare:Development and test of new metallic alloys for production wells;Test of coatings for water and gas injection well tubing;Alternative routes for fabrication of metallurgically bonded pipes;Use of non-metallic materials for risers. Introduction The impact of Presalt Discovery Offshore Brazil The Brazilian offshore province began to attract the attention of the oilindustry a couple of decades ago. Since then, the development of giantdeepwater fields in Campos Basin such as Marlim, Albacora and Roncador haveproved the basin potential (Ref.1, 2). But this potential seems to have reacheda new scale in 2006, with the huge Tupi discovery (later on renamed as LulaField, complying with to Brazilian Law that requires that oilfields take thenames of sea animals). The Lula field is located in Santos Basin deep waters(2,200m), south of Campos Basin, below a salt layer which, in some locationsreaches more than 2,000m thick (Fig. 1). The Lula Field alone has estimatedtotal reserves of more than 6 billion boe and. other discoveries in SantosBasin adjacent explorations blocks, such as Guará, Iracema (located in the sameexploration block as Lula), Carioca and others, have confirmed how prolificthis new province was. Moreover, as the salt layer extends north of SantosBasin, into Campos and EspÍrito Santo Basins (Fig. 2), several discoveries weremade in Presalt layers of these Basins, including areas where oil was alreadybeing produced (from post-salt reservoirs) such as Jubarte Field, in EspÍritoSanto, allowing fast connection of the new pre-salt wells to existingproduction facilities.
The interest in renewable and cleaner fuels has stimulated ethanol production in the last decades. Some of the drivers for that ever increasing production were the Brazilian Alcohol Program, Kyoto Protocol and the replacement in USA of the octane booster MBTE (methyl-tert-buthyl ether) for ethanol. The world’s largest producers of ethanol are The United States of America and Brazil, where the main sources are corn and sugar cane, respectively. Production flow via pipeline is the safest and most cost effective way to connect the producers, usually spread across the country, to the distribution terminals. However, in USA there are evidences that ethanol may have caused stress corrosion cracking (SCC) in pipelines and also in storage tanks. Controversially, in Brazil ethanol has been transported and stored since the 1970’s without any indication of SCC. The aim of this work is to evaluate the susceptibility of the steel API 5L X70 [1] to SCC in different ethanol (corn and sugar cane) using slow strain rate testing (SSRT). These tests were carried out on notched specimens according to NACE TM 0111 [2]. The SSRT results carried out in corn ethanol have shown a considerable reduction of plastic elongation and a mixed fracture micromechanism of quasi-cleavage and intergranular facets clearly indicating a susceptibility of the API 5L X70 steel to SCC. The SSRT also demonstrated that the carbon steel tested here is completely immune to SCC in sugar cane ethanol.
Stress corrosion cracking (SCC) of UNS S31603 austenitic stainless steel (ASS), UNS S32205 duplex stainless steel (DSS) and UNS S32750 super duplex stainless steel (SDSS) was investigated. SCC tests were carried out at 110 ºC for 500 h under drops of synthetic seawater (DET, drop evaporation test). Two loading conditions were investigated: 50 % and 100 % of the experimental yield strength of each steel. DSS and SDSS specimens showed no susceptibility to SCC under loading of 50 % of their yield strength, contrary to ASS, but all steels fractured at the highest load. SCC nucleated under the salt deposit formed on the surface of all specimens. SCC propagation was mainly transgranular, but SCC propagation of DSS also featured crack ramification in the austenite phase. In addition, SDSS also presented crack propagation along the ferrite/austenite interfaces. Transgranular cleavage fracture was also observed in all fractured specimens, but DSS also presented ferrite/austenite interfacial brittle fracture, while SDSS also featured intergranular brittle fracture.
The usage of superduplex stainless steels in offshore petroleum production has increased considerably in the last years. Particularly, the use as flowline pipes for oil production needs careful research on the effect of critical environmental conditions on the stress corrosion resistance of welded joints. In this work, welded joints of UNS S32750 were produced by automatic gas tungsten arc welding (GTAW-orbital) using a J-groove weld geometry. The welded joints were evaluated using slow strain rate tensile tests in acid solutions containing hydrogen sulfide (H 2 S) and chloride. H 2 S partial pressure and pH were varied to determine safe operating conditions. Specimens tested at pH = 3.5 and p(H 2 S) = 3.75 and 6.75 showed brittle behavior. The specimens tested with lower p(H 2 S) or higher pH exhibited ductile behavior. KEY WORDS: gas tungsten arc welding, slow strain rate tensile test, sour solutions, sulfide stress corrosion, superduplex stainless steel ISSN 0010-9312 (print), 1938-159X (online) 12/000011/$5.00+$0.50/0 © 2012, NACE International CORROSION SCIENCE SECTION
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