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INTRODUCTION ABSTRACT Operators of pipelines and buried plant piping are often faced with the challenge of prioritizing locations for assessment and selecting defensible intervals for reassessment. Technical staff that are responsible for corrosion mitigation recognize that understanding the effect of the soil on buried structures is a critical component in developing a representative picture of the external corrosion potential of buried structures. However, it is not always apparent how to use soil analysis data effectively in buried piping programs or how to integrate pipe polarization data in establishing reinspection intervals. This paper addresses how soil analyses and related corrosion rate modeling can be integrated with indirect inspections (i.e., above ground surveys) data so that locations can be prioritized for further examination and assessment, and how the results of the modeling can be used as a substitute for default corrosion rates when setting reinspection intervals. The soil corrosiveness model developed for this purpose was derived from empirical data relating twenty-two soil and cathodic protection polarization attributes to long term corrosion pitting rates on buried steel pipe. We present a sampling approach that has proven effective in gathering information useful in corrosion evaluations, and we include discussion of the factors to consider when selecting locations for sampling and the soil sample collection and analysis process itself. Finally we describe the integration of the soil data with cathodic protection data to 1) rank the severity of the likely corrosion at each location and 2) provide quantitative estimates of the corrosion rate at each location. The integration of data is recognized as an essential aspect of direct assessment for pipeline integrity management. It is generally understood that for external corrosion to be likely in a buried piping application, a susceptible material (presumed to be a carbon steel pipeline), must be in contact with a corrosive environment (i.e., soil) to support a corrosion reaction. The first line of defense against external corrosion is addressed through the application of a coating system suitable for a buried environment. Over time, damage and degradation of the coating exposes the bare pipeline to the environment. To mitigate the potential for metal loss, cathodic protection (CP) is applied. (Figure in full paper) As Figure 1 depicts, identifying and prioritizing examination sites with the greatest likelihood of corrosion is assumed to be the location with the lowest polarization. If the CP system is effective, one would not anticipate metal loss. Instead, sites with ineffective CP performance would be considered. However, soil corrosivity can have a significant affect in selecting between the sites that have ineffective CP. In plant settings, all piping systems, buried or otherwise, are grounded to one another and to a copper grounding grid for safety purposes. This type of configuration reduces the effectiveness of traditional indirect inspection techniques such as close interval surveys. In addition, CP systems are often times unable to provide sufficient current to achieve a consistent -850 mV measured pipe to soil value.
- Research Report > New Finding (0.47)
- Research Report > Experimental Study (0.34)
- Materials (1.00)
- Food & Agriculture > Agriculture (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT All the current techniques used to measure the metallic corrosion require contact with the metal. Particularly, in the case of reinforcement corrosion, this signifies the need to reach the bar that is embedded in the concrete, which may consequently result in the disruption of the integrity of the real structures. This paper explores the feasibility of using a new method for polarizing the reinforcement or any metal in an electrolyte, without the need of direct contact with it. The polarization is obtained through the induction of current from an external electrical field. The current runs through the electrolyte and the metal in parallel, depending on the electrode arrangement. The resulting Polarization Resistance calculated is termed as Inductive, Rp= Rpi. The Inductive is calculated by the model of resistances in parallel, which requires a separate measurement of the electrolyte ohmic resistance. In this study, solutions with several resistivities and concrete specimens with and without chlorides have been used. The results indicate that electrolytes of low resistivity mask the measurement, and consequently, Rpicould not be calculated. In electrolytes with high resistivity, such as concrete, the feasibility is found to depend on the relative values of Re and Rpi. INTRODUCTION The measurement of instantaneous corrosion rate, proposed by Stern et al. [1], who developed the so-called Polarization Resistance or Linear Polarization, Rptechnique, is based on the theory of mixed potential put forth by Wagner and Traud [2]. This method determines the corrosion current through the measurement of the slope of the polarization curve around the corrosion or mixed potential, in such a way that the polarization applied to the metal is small enough such that it cannot alter the corrosion process: Rp= ?E/?/ when ?E?0 and Icorr= BRp, where B is a constant that varies from 13 to 52 mV. Thus, the Rptechnique is non-destructive in nature, which has been the main reason for its rapid generalized use in numerous metal/electrolyte systems [3][4]. In particular, this technique was applied to measure the reinforcement corrosion in the 1970s [5][6]. To polarize the metal to measure its Rp(or charge transfer resistance, RT), it is necessary to make contact with the metal, considering it as the working electrode. However, in an earlier study [7], a method that gives the Rpvalue without making physical contact with the metal was described. This method was termed as non-contacting method (NCCm), and was calibrated by gravimetric studies in distilled water-rebar considered as the metal-electrolyte system. In this paper, this method has been applied to different metal/electrolyte systems and concrete slabs to explore the limits of its application. Furthermore, the resulting values have been compared with those obtained by other contacting on site techniques [8][9][10]. EXPERIMENTAL To explore the possibilities of applying this method to different electrolytes, cells that are prepared with solutions of different resistivities, in which the steel corrodes at different rates were used. Furthermore, the concrete specimens were also prepared.
Characterization And Optimization Of The Functional Properties Of Stainless Steel Surfaces
Ladwein, Thomas L. (Aalen University of Applied Sciences) | Sorg, Matthias (Aalen University of Applied Sciences) | Schilling, Sebastian (Aalen University of Applied Sciences) | Schilling, Sybille (Aalen University of Applied Sciences)
INTRODUCTION ABSTRACT The passivation behavior of 304L, 316L and 22 %Cr duplex stainless steel has been studied as a function of mechanical. chemical and/or.electrochemical treatment. Surface energies, impedance spectra and pitting potentials were evaluated as measures to characterize the functional surface properties. Specimen blasted with glass beads always performed better than those blasted with alumina. Nitric acid has no long time benefits as a passivating agent. The influence of citric acid on the passive behavior is marginal and does in the long run not at all reach that of a air-only passivated specimen. Stainless steels owe their functional properties to the formation of a passive layer on the surface. The properties of this passive layer are very much dependent on the alloying content, but can also largely be influenced by mechanical and chemical finishing processes. These finishing treatments are made after producing the material in the steel mills and/or after further processing into the final products. In both cases mechanical treatments are mostly the first step which is followed by a chemical reaction, either by applying chemicals in form of spray, pastes or by immersion, or by reacting the steel with the oygen in the air without any further deliberate action. Commonly used chemicals are reducing acids like sulfuric or hydrofluoric, oxidizing acids, especially nitric acid, mixtures of reducing and oxidizing acids and complex formers like citric acids. The reactions with the steels vary with the character of the reagents, and are also influenced by the preceding mechanical treatment, whether grinding, blasting, polishing etc. In should also be kept in mind, that in most cases any treatment is followed by an - undeliberate - after treatment in contact with air. This latter is a rather slow reaction. Therefore it is important, when evaluating the passive properties of a stainless material, to understand the history of the material before the moment of the evaluation. Earlier work has shown that tools useful for determining the functional passive properties of stainless steels are electrochemical measurements such as linear polarization and deriving the critical pitting potential therefrom, electrochemical noise and electrochemical impedance measurements, determinations of the surface energy and also measurements of the surface topography. A combination of these measurements should help to understand the interactions of the various treatments and their influence on the functional passive properties of stainless steels. Test Materials EXPERIMENTAL Test specimens were cut in sizes 20x20 mm from a cold rolled sheet (3 mm thick) of stainless steel 1.4404 (AISI 316L), from a hot-rolled 1.4307 (AISI 304L) and a hot-rolled 1.4462 (UNS S 32205) in the as delivered condition. A copper wire was spot welded from the backside and the specimen mounted in a metallografic sample using an epoxy resin which permits a gap-free mounting. Surface preparations were applied by wet-grinding the specimen on a metallografic disc using emery paper of various grits and applying a defined force in all cases. The blasting was done with glass beads (70-110µm) and alumina (corundum) (53-75µm).
- North America > United States (0.17)
- Europe > Germany (0.15)
- Materials > Metals & Mining > Steel (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.35)