Guide Techno-protection


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Guide Techno-protection - 1

Corrosion process The Corrosion is the result of a chemical or electrochemical reaction between a metal and it’s environment, which produces a deterioration of the metal and it’s properties. The identity of a metal is determined by its corrosion potential and is measured in millivolts. This measurement may vary from one zone to another depending on the surrounding medium. The zone where the corrosion process may be initiated is known as the anodic zone. An anodic zone is defined by the most negative potential. The corrosion of a metal is an oxidization process called an anodic reaction. A cathodic zone creates a secondary process known as the cathodic reaction. This is a reduction process by which the electrons created by the anodic reaction is consumed, resulting in the two processes balancing their charges. Fe Fe2+ + 2e- In order for the corrosion process to occur, there must be an anodic zone and a cathodic zone. Depending on the circumstances, these two zones can be positioned close together on a metal’s surface, or far apart. The two zones co-exist creating an electrochemical process in which the surrounding medium acts as a transport system for ions. This pathway is defined as the electrolyte. One of the key elements for the corrosion process is the soil surrounding the metal surface. In addition to the soil being an electrolyte, the properties of the soil may inhibit or enhance the corrosion. Such processes including soil resistivity (velocity of the current traveling through the ground), directly effect the formation, rate and placement of corrosion on the metal surface. A less resistive soil, results in an accelerated corrosion reaction. Furthermore, soils with the following parameters may also influence the location and formation of the anodic zones. • Low oxygenated soil • Ground of low resistivity • Presence of sulfato-reducing bacteria • Soil saturated with water • Organic contamination (compost, refuse, ...) • Contact with highly conductive materials (ashes,coal,salts, ...) • Dissimilar materials Cathodic zone Corrosion Anodic zone soil Metallic structure Transfert of electrons Iron dissolution

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Guide Techno-protection - 2

On a metal structure placed in a soil environment, localized corrosion attacks are a particular concern. The metal structure may go through numerous layers of soil. With every layer there is a transition in soil composition, shifting aggressiveness with varying layers of resistivity. These resistive regions (both anodic and cathodic) typically decrease with incremental depth, however the corrosion process will be amplified on the metal structure where the various layers of soil intersect. In understanding the corrosion process and the various elements involved that directly effect this...

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Guide Techno-protection - 3

INTRODUCTION Techno protection is a well known electrochemical technique using the cathodic protection concept for stopping the corrosion process of underground metallic structures. METHODOLOGY The techno protection can be applied via two methods: 1)Techno protection impressed current (TPIM) The TPIM works by using anodes composed of a noble metal that is fed by an external current source such as a rectifier. Through the rectifier, a voltage is applied to the structure that, in turn, generates a potential difference between the structure and the anodes. This difference protects the metal...

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Guide Techno-protection - 4

Techno protection imposed current (TPIM) The Techno Protection Impressed Current application is an electrochemical technique, which inclusively transforms all of the metal stuctures in to a permanent cathodic state. By implementing an external source of current, the rectifier, controls and maintains polarization of the metal stuctures in an effective manner. With the introduction of a foreign anodic zone, the anode, a cathodic zone is created on the metal stuctures surface, which provides a controlled immunity from natural corrosive influences. This Techno Protection application ensures an...

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Guide Techno-protection - 5

Techno protection by sacrificial anodes (TPSA) This Techno Protection by sacrificial anode application utilizes the intrinsic characteristics of the anode system to polarize the metal stuctures. By implementing this electrochemical technique the metal stuctures are brought completely to a cathodic state. The introduction of a foreign anodic zone, the sacrificial anode, a cathodic zone is created on the metal stuctures surface that provides a controlled immunity from natural corrosive influences. This Techno Protection application ensures a distinct extension of the service life expectancy...

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