Mariano Iannuzzi

Aluminum Alloy Corrosion Inhibition by Vanadates

The inhibition of Al alloy corrosion by vanadates was studied in this work. Vanadium speciation is very complicated and vital to the inhibition efficacy. Critical conditions for decavanadate polymerization from clear metavanadate solutions were investigated. Decavanadate only formed when metavanadate was added to solutions of pH 3 or less. It was not possible to change the pH of a metavanadate solution without forming decavanadates, creating an orange-colored solution. According to 51 V nuclear magnetic resonance, monovanadates were present only in clear metavanadate solutions; orange solutions always contained decavanadates and never contained monovanadates. Orange decavanadate solutions containing 0.5 M NaCl at pH 8.71 exhibited no significant inhibition of the oxygen reduction reaction and increasing decavanadate concentration was detrimental. In contrast, clear metavanadate solutions containing monovanadate exhibited strong inhibition of the oxygen reduction reaction, to a level similar to chromate. At a fixed pH, increased NaVO3 concentration in clear metavanadate solutions increased inhibition efficiency.

Pre-Exposure Embrittlement and Stress Corrosion Cracking of Magnesium Alloy AZ31B in Chloride Solutions

Stress corrosion cracking of the Mg-Al-Zn AZ31B (UNS M11311) alloy was studied in sodium chloride (NaCl) solutions at different potentials and NaCl concentrations using the slow strain rate technique. Results showed that stress-strain curves were similar despite changes in potential and chloride concentration. In addition, pre-exposure tests were performed in NaCl solutions at the open-circuit potential followed by immediate straining or straining after a dry-air exposure delay. The dependence of ductility with pre-exposure time, the reversibility of embrittlement, and the fracture surface of pre-exposed samples suggested that the AZ31B alloy was susceptible to internal hydrogen embrittlement. Stress corrosion cracking and the pre-exposure embrittlement of this alloy in NaCl environments are explained assuming that crack growth rate was controlled by hydrogen diffusion.

Materials and corrosion trends in offshore and subsea oil and gas production

The ever-growing energy demand requires the exploration and the safe, profitable exploitation of unconventional reserves. The extreme environments of some of these unique prospects challenge the boundaries of traditional engineering alloys, as well as our understanding of the underlying degradation mechanisms that could lead to a failure. Despite their complexity, high-pressure and high-temperature, deep and ultra-deep, pre-salt, and Arctic reservoirs represent the most important source of innovation regarding materials technology, design methodologies, and corrosion control strategies. This paper provides an overview of trends in materials and corrosion research and development, with focus on subsea production but applicable to the entire industry. Emphasis is given to environmentally assisted cracking of high strength alloys and advanced characterization techniques based on in situ electrochemical nanoindentation and cantilever bending testing for the study of microstructure-environment interactions.

Use of the Critical Acidification Model to Estimate Critical Localized Corrosion Potentials of Duplex Stainless Steels

Crevice corrosion affects the integrity of stainless steels used in components exposed to seawater. Traditionally, crevice corrosion testing involves the use of artificial crevice formers to obtain a critical crevice potential, which is a measure of the crevice corrosion resistance of the alloy. The critical acidification model proposed by Galvele predicts that the critical crevice potential is the minimum potential required to maintain an acidic solution with a critical pH inside either a pit or a crevice. Application of Galvele’s model requires an estimation of both the diffusion length and the i vs. E behavior of the metal in the solution inside the crevice. In this work, the crevice corrosion resistance of a 22%Cr duplex stainless steel (UNS S31803) and a 25%Cr super duplex stainless steels (UNS S32750) was investigated. The i vs. E response of the two stainless steels was determined in acidified solutions of various chloride concentrations, which simulate those found in an active crevice. Critical po...

Sulfide stress cracking of nickel-containing low-alloy steels

Abstract Low-alloy steels (LAS) are extensively used in oil and gas (O&G) production due to their good mechanical properties and low cost. Even though nickel improves mechanical properties and hardenability with low penalty on weldability, which is critical for large subsea components, nickel content cannot exceed 1-wt% when used in sour service applications. The ISO 15156-2 standard limits the nickel content in LAS on the assumption that nickel concentrations above 1-wt% negatively impact sulfide stress cracking (SSC) resistance. This restriction excludes a significant number of high-strength and high-toughness alloys, such as Ni-Cr-Mo (e.g., UNS G43200 and G43400), Ni-Mo (e.g., UNS G46200), and Ni-Cr-Mo-V grades, from sour service applications and can be used only if successfully qualified. However, the standard is based on controversial research conducted more than 40 years ago. Since then, researchers have suggested that it is the microstructure that determines SSC resistance, regardless of Ni content. This review summarizes the advantages and disadvantages of nickel-containing LAS in terms of strength, weldability, hardenability, potential weight savings, and cost reduction. Likewise, the state of knowledge on the effect of nickel on hydrogen absorption as well as SSC initiation and propagation kinetics is critically reviewed.

Erratum: Sulfide stress cracking of nickel-containing low-alloy steels (Corrosion Reviews (2014) 32:34 (101-128) DOI: 10.1515/corrrev-2014-0027)

*Corresponding author: Mariano Kappes, Comisión Nacional de Energía Atómica, Instituto Sabato (UNSAM/CNEA), Av. Gral. Paz 1499, San Martín, Buenos Aires 1650, Argentina, e-mail: marianokappes@gmail.com Mariano Iannuzzi: General Electric, Oil and Gas, Eyvind Lyches vei 10, Sandvika, Bærum NO1338, Norway Raúl B. Rebak: General Electric, Global Research Center, 1 Research Circle, Schenectady, NY 12309, USA Ricardo M. Carranza: Comisión Nacional de Energía Atómica, Instituto Sabato (UNSAM/CNEA), Av. Gral. Paz 1499, San Martín, Buenos Aires 1650, Argentina Corrigendum