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Results
Evaluation Of Ac Corrosion In Pipelines Buried Using Ac-Probe
Panossian, Zehbour (Researcher Institute for Technological Research) | Laurino, Eduardo W. (Consultant Petrobras/Transpetro) | Abud Filho, Sérgio E. (Researcher Institute for Technological Research) | de L.Oliver, João Hipólito (Consultant Petrobras/Transpetro) | de Almeida, Neusvaldo L. (Researcher Institute for Technological Research) | de S.Pimenta, Gutemberg (Consultant Petrobras/Cenpes) | P.Filho, Mário Leite (Researcher Institute for Technological Research) | de C.Albertini, José Álvaro (Enginnering Petrobras/Transpetro) | de L.Silva, Diogo (Technical Institute for Technological Research)
ABSTRACT: Corrosion by alternating current in buried pipelines has been investigated for several years since the first AC-induced corrosion failure in the 60's. After this occurrence, many research groups have been studied the phenomena in order to understand the mechanism and to purpose reliable criteria to access the probability of AC-induced corrosion in buried pipelines. However, the proposed criteria are contradictory and inefficient because they consider the influence of direct and alternating stray currents separately. In order to purpose a reliable criterion for AC-induced corrosion, it is necessary to consider the coupling between DC and AC currents. Thus, the field measurements should give information about the level of AC interference, the cathodic protection potential, the level of the DC and AC potential coupling and all this measurements must be carried out without the IR-drop influence. This work has as an objective to describe a new technique developed to verify the thermodynamic probability of AC-induced corrosion. Field results obtained through the described new technique are presented and discussed. INTRODUCTION AC-induced corrosion has been studied by corrosion experts for many years1. Consequently, there are many papers describing laboratory and field studies concerning the phenomenon of AC-induced corrosion of buried pipelines and several propositions are presented on the mechanisms of this type of corrosion. An important manual, published by CEOCOR in 2001 2, deals with the corrosion phenomenon as such and presents guidelines for risk assessments and mitigation measures. A recently published guide 3 presents an overview of the state-of-art of AC-induced corrosion as well as field measurement procedures and countermeasures for the mitigation of AC-induced corrosion on metallic pipelines. One of the main objectives of this guide is to emphasize the casual link with the AC power lines, overhead lines or cables and to facilitate communication between professionals working in the areas of electricity transmission and cathodic protection. Buried pipelines are usually painted with anticorrosive organic coatings and cathodically protected. The latter negatively polarizes the metal to be protected and operates in the regions where the organic coating presents defects preventing corrosion of the metallic substrate. The combination of these two preventive measures provides the durability of the metallic substrate. The intensity of this current will depend on the system impedance. During the positive cycle of AC voltage, the current will flow from the metal into the electrolyte. If the current intensity is sufficiently high, the corrosion of the metal will occur in acidic conditions and possible metal passivation with oxygen evolution will occur in alkaline conditions (anodic cycle) 4. During the negative cycle of AC voltage, the current will flow from the electrolyte into the metal and will cause an overprotection, the higher the current, the higher the overprotection (cathodic cycle). Figure 1a shows, schematically, the potential of a cathodically protected pipeline free of AC current interference and Figure 1b shows the waveform of the ACpotential interference in a cathodically protected pipeline, as well as the cycles responsible for the corrosion (or passivation) and the overprotection, respectively.
- South America > Brazil (0.50)
- North America > United States > Texas (0.28)
Effect of Inert Gases (Pure Nitrogen, Nitrogen And Carbon Dioxide Mixtures) On the Corrosiveness of Anhydrous Ethanol (E100)
Moreira, Anna Ramus (IPT Institute for Technological Research) | Panossian, Zehbour (IPT Institute for Technological Research) | Pimenta, Gutemberg Souza (Petrobras) | de Oliveira, Viviane (INT National Institute of Technology) | Brugnelli, Renata Angelon (IPT Institute for Technological Research)
INTRODUCTION ABSTRACT The objective of this work was to study the effect of inert gases (pure nitrogen, nitrogen and carbon dioxide mixtures) on the corrosiveness of anhydrous ethanol (E100) through laboratory tests. Initially, preliminary tests were conducted in order to establish the test conditions which showed that inerting tests must be done in hermetic cells. After methodology establishment, seven E100 lots were tested. The obtained results showed that different lots of N2 inerted E100 present different corrosiveness to carbon steel; CO2 injection in E100 provides an increase in its acidity, but this increase is not responsible for its corrosiveness; for nonaggressive N2 inerted E100, the presence of CO2 does not cause a deleterious effect; for aggressive N2 inerted E100, the presence of CO2 causes a slight intensification of corrosion (the higher the CO2 content in the inert gas, the greater the corrosion rate); crevices enhance corrosion process of carbon steel by E100; the corrosion rate of carbon steel, even in aggressive N2 inerted E100, are negligible. Thus, for short-term inerting corrosion tests, the weight loss is not an adequate response for the evaluation of E100 aggressiveness. Detailed visual inspection and maximum pit depth determination are more prone for this purpose Anhydrous ethanol (E100) is an important option, worldwide, as an alternative source of renewable energy, due to its advantages such as being a renewable natural source as well as an environmentally friendly fuel. In this sense, Brazil is already known as a potential E100 producer to supply national and international needs, not only to maintain this scenario but also to become one of the world's biggest ethanol exporters. In Brazil itself, E100 may be transported by means of trucks or pipes; whereas ships are used to transport it to foreign countries. To distant places, barges are used for economical purposes. Thus, for E100 exportation, security standards must be in agreement with the International Convention for the Safety of Life at Sea - SOLAS which is an organization that establishes minimum standards for ships construction, security equipments, emergency procedures, ship inspections and certificate emissions. Regarding maritime fuel transportation, SOLAS stipulates that, when the volume is over 20,000 tons, it is necessary to inert the tanks in order to avoid fire and explosion as well as maintaining the quality of the cargo1,2,3. In practice, ship tank inerting is done with nitrogen gas (N2) and gas mixtures such as N2 and carbon dioxide (CO2) or N2 and argon (Ar)3. Inerting gases may be produced in industrial plants or by using shipboard generators. In general, shipboard generators produce N2 with 15 % CO2 and are the most widely used due to their simplicity, high production capacity and their low initial cost3. Another alternative is the usage of gases generated by shipboard boilers, which also contain CO2. Whatever the inert gas is, one must have the guarantee that the cargo quality is not altered.
- Materials > Chemicals > Industrial Gases (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Renewable > Biofuel > Ethanol (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Reservoir Description and Dynamics (1.00)
- Health, Safety, Environment & Sustainability (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)