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Abstract The heat-treatable and weldable alpha-beta titanium alloy, UNS R55400, was developed as a higher strength alternative to the highly corrosion-resistant UNS R56404 (ASTM Grade 29) titanium alloy used as tubular components for corrosive, extreme high pressure, high temperature (XHPHT) and deep water hydrocarbon production service. Recently approved for sour service, this alloy exhibits very comparable resistance to UNS R56404 in acidic, sour and non-sour chloride-rich aqueous environments commonly associated with upstream and offshore hydrocarbon production. This paper presents an expanded laboratory test database on critical corrosion modes for UNS R55400 pipe exposed to relevant oilfield production environments which include sour well fluid brines, a heavy chloride/bromide brine well completion fluid, injected methanol, organic acid- and HCl-based well acidizing solutions, and seawater. The alloy’s elevated reducing acid chloride resistance exhibited in these tests is correlated with electrochemical parameters derived from cathodic/anodic polarization testing and alloy corrosion rates derived from dilute boiling HCl media. Corrosion performance comparison between UNS R55400 and other common high strength oilfield titanium alloys is made across these specific production service environments to provide guidance for alloy selection and use. Introduction The new UNS R55400 titanium alloy was developed as a higher strength alternative to ASTM Grade 29 titanium (UNS R56404) for highly stressed tubular and forged components used in corrosive, high pressure, high temperature (HPHT) energy extraction service. Relevant, projected applications include offshore production risers, deepwater well-work over/completion/landing, tubular strings, drill pipe strings, and deep sour HPHT well Oil Country Tubular Goods (OCTG)/production tubing and liners. This heat-treatable alpha-beta titanium alloy features higher strength (862 or 896 MPa minimum yield strength), elevated strength-to-density for lighter weight components, and an overall corrosion resistance similar to that of UNS R56404. With the nominal composition in weight percent of Ti-5.5Al-4.3Zr-5.7V-1.3Mo-0.10 O-0.06Pd, this extra low interstitial (ELI) alloy formulation ennobled via minor Pd addition was designed to resist crevice and stress corrosion, and provide good fracture resistance in aqueous chloride environments up to ~300°C, while being highly weldable via fusion or solid-state welding methods.
- Geology > Geological Subdiscipline > Geomechanics (0.46)
- Geology > Mineral > Halide (0.34)
Abstract Titanium is used for many applications, ranging from chemical, to biomedical, to decorative ones. Its versatility is due to its excellent specific mechanical resistance, high durability and biocompatibility. Titanium presents excellent corrosion resistance in natural environments thanks to the presence of a well protective passive layer of TiO2, but its use in industrial environments may require a significantly better behavior with respect to what is commonly observed. By means of anodic oxidation it is possible to increase at the metal surface the thickness of TiO2, increasing the barrier effect. This research aims to study the surface modification of titanium alloys in order to increase the pure titanium durability in highly aggressive environment and to obtain a potential economical alternative to titanium-palladium alloys currently on the market. Introduction Titanium presents an outstanding corrosion resistance, which is ascribed to the thin, protective oxide layer that forms spontaneously on its surface when exposed to the air . On account of such behavior, this metal and its alloys are generally used in severe conditions, e.g., in acid environments, or in presence of high concentrations of corrosive agents (chlorides, fluorides), often in combination with high temperatures. This is the typical case of the desalination plants heat exchangers, mainly multistage flashing (MSF) ones, where the use of titanium allows reducing tubes thickness and improving the components service life. Still, in such aggressive conditions, the natural corrosion resistance of titanium is not always sufficient, in particular considering pitting and crevice corrosion in hot seawater and brine. To solve these issues, industries are forced to move to very expensive titanium alloys, specifically the palladium containing alloy (UNS R52400, which contains 0.12-0.25% by weight of palladium, Figure 1) . Unfortunately, alloying titanium with palladium involves a not negligible increase in production costs associated. On the other hand, in the last decades much work has been done on the optimization of titanium surfaces, focusing on the increase in thickness of the amorphous oxide layer and to modify its morphology and structure, in order to either improve its corrosion resistance or generate new properties strictly correlated to the obtaining of a crystalline oxide .