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Abstract a Land Ke Hr | Electrochemistry | Corrosion

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   1  Fusion-Bonded Epoxy (FBE) and Dual-Layer FBE MaterialsProvide Enhanced Performance for Pipeline Installation   By: J. Alan Kehr, Martin Rau, and Emran Siddiqui; 3M Company SUMMARY Fusion Bonded Epoxy (FBE) and 3 Layer Polyolefin (3LPO) are the most commonly used pipeline coatings in the world. Over the last few years, dual Layer FBE (DLFBE) coatingshave seen more use because of combining properties of a coating that is non-shielding tocathodic protection and the low-cost economics of FBE with damage resistance approachingthat of 3 Layer Polypropylene (3LPP) and 3 Layer Polyethylene (3LPE). FBE BASED COATING SYSTEMSFBE Single Layer. Since first introduced in 1960, single-layer FBE has proven its capabilityas a pipeline coating and is now the most commonly used pipeline coating in North America.It not only has the performance characteristics important to the application and construction processes, but also has proven performance in underground and undersea service over a long period of time. It has proven effective for line pipe, girthwelds, fittings, and bends. Whenused at a greater thickness, it has worked effectively with weight concrete and directional- bore installations. FBE Two Layer. Utilizing two layers of FBE provides great versatility in coatings for  pipeline protection. Two-layer FBE systems utilize the application of a second FBE on top of the base FBE corrosion coating. The top layer typically, but not necessarily, is depositedduring the melt (pre-gelation) stage of the primary layer. The result is an intimate chemical bond between the two layers. A significant advantage of multilayer technology is that uniquecharacteristics can be developed by selection of different coating layers with specific properties. Each layer can be designed to impart specific characteristics that combine to produce performance results that significantly exceed those of a single-layer coating.The first layer has the properties of a standalone FBE coating, providing excellent adhesionand resistance to cathodic disbondment. The top layer provides mechanical damage resistancefrom impact or gouging during handling, transportation, and construction. The combination provides the contractor faster, worry-free installation and the pipeline owner with improvedunderground coating performance. This system has been used successfully with impingementand compression-wrapped weight concrete applications. The pipeline construction servicesindustry has created girthweld coating application systems that can apply dual-layer FBE inthe field so that the entire pipeline has the same coating.   2 Pipeline Coatings - Usage History 1960 1970 1980 1990 2000 FBEFBE - Dual Layer3-Layer PE/PP    C  o  a   t   i  n  g   M  a   t  e  r   i  a   l Year Three-layer FBE   primedpolyolefin coatings .Introduced in the late1970s, 3-layer polyolefincoatings were put into practice around 1980. Thiscoating system is based onearlier pipeline coatingsand combines FBE and polyolefin materials tooffer customized systemsdesigned to fulfilenvironment requirements.This system is an effectivesolution in situations whereextraordinary coatingdamage is highly probableor elevated temperatureservice is likely.The three types of FBE based coating systems have a relatively long history as seen in Figure1. MECHANISM OF CORROSION One general definition of corrosion is the degradation of a material through environmentalinteraction.As extracted from its ores (metal oxides: Hematite Fe 2 O 3 , Bauxite Al 2 O 3· H 2 O), a significantamount of energy is put into metal placing it in a high energy state. In accordance to one of the principles of thermodynamics, materials will always seek the lowest energy state. In caseof metals they tend to lose their energy by reverting to compounds more or less similar totheir srcinal states, which in most cases is an oxide or some other compound. This process bywhich metals convert to the lower energy oxides is called corrosion. Corrosion occurs for most common engineering materials at ambient temperatures in water-containingenvironments. The aqueous environment and its electrochemical nature are also referred to asthe electrolyte and, in case of underground pipelines, is the moist soil.The corrosion reaction chemistry is electrochemical in nature. When metal atoms are exposedto an environment containing water molecules, they can give up electrons (oxidation) becoming themselves positively charged ions provided that an electrical circuit can becompleted. The oxidation is called the anodic reaction. The consumption of those electrons bythe reduction reaction of oxygen or water is commonly called the cathodic reaction. Theoxidation reaction causes the actual metal loss, but the reduction reaction must be present toconsume the electrons liberated by the oxidation, maintaining charge neutrality. Otherwise, alarge negative charge would rapidly develop between metal and electrolyte and the corrosion process would cease. CORROSION PREVENTION The principal methods for corrosion prevention on underground pipelines are coatings andcathodic protection. Figure 1. A truncated history of pipeline coatings.   3  Coatings   are intended to form a continuous film of an electrical insulating material over themetallic surface to be protected. The function of such a coating is to isolate the metal fromdirect contact with the electrolyte, interposing a high electrical resistance so thatelectrochemical reactions cannot occur.FBE systems are effective in the prevention of underfilm corrosion due to their excellent barrier properties including low oxygen permeability. Oxygen permeability of FBE is lessthan one-fifth that of polyethylene. However, FBE coatings have a higher moisture permeability rate than PE coatings. Cathodic Protection (CP) is a technique to reduce the corrosion rate of a metal surface bymaking it the cathode of an electrochemical cell. This is realized by shifting the potential of the metal in the negative direction by use of an external power source. For CP to work,current must be discharged from an earth connection called a ground bed. In the process of discharging the current in a sacrificial system, the anodes in the ground bed are consumed bycorrosion. COATINGS   Single Layer FBE . Since a New Mexico company coated the first FBE pipeline in 1960, thistechnology is now the number one pipeline-coating in North America. It is used on pipes, bends, girthwelds, and fittings. It is also used in the oil, gas, and water markets. It has beeninstalled in the ocean, the arctic, in the mountains and in the plains. 1 Figure 2   shows theimprovement in cathodic disbondment resistance of FBE pipecoatings in the last fifty years. FBE Cathodic-Disbondment-Resistance Improves with Chemistry 90 days, 23 o C, 3% ASTM G 8 electrolyte, -1.5 V05101520253035196519801995Year     C  a   t   h  o   d   i  c   D   i  s   b  o  n   d  m  e  n   t  -  m  m  r   Figure 2. There have been significant improvements in FBE coating technology in thenearly fifty years in the market.   4 Long years of experience demonstrate the following benefits for single layer FBE:1.   Excellent adhesion to steel; good chemical resistance2.    Non-shielding to CP – if it fails, it fails friendly3.    No reported cases of stress-corrosion cracking (SCC) of pipe coated with FBE4.   Resistant to biological, insect, termite, and root attack 5.   Installation friendly ã   Excellent penetration resistance, good abrasion and gouge resistance ã   Good impact resistance o   Impact damage is limited to the point of contact o   Damage is easily seen   o   Damage is easily repaired ã   Good flexibility Dual Layer FBE . The first dual-layer FBE (DLFBE), introduced in 1992, was for high-operating temperature pipelines. That was followed in 1998 by the first abrasion resistantouter (ARO) coating for directional drill pipeline installation. DLFBE, see Figure 3 maintainsthe excellent performance and installation characteristics of single-layer FBE, but provideseven better damage resistance, with a slight reduction in flexibility. The dual-layer system provides many of the advantages of three-layer systems – see Table 1.The ARO system utilizes a high performance FBE as a base layer with a top coat of amechanically hard FBE, which ensures a tough outer layer resistant to gouge, impact,abrasion and penetration. Today’s dual FBE system is sometimes used for the entire pipe linelength (Kern River project, 1150 km of 30 and 42 inch pipe at a nominal thickness of 500microns; Koyali-Ratlam pipeline Project in India, 262 km). Figure 3. Dual Layer FBE system The relative cost between single-layer FBE, dual layer FBE, and three-layer polyolefincoating systems depend on many variables, such as: commodity (solid epoxy, PE) costs thataffect coating materials, applicator plant productivity, and coating thickness specifications.Those costs will also vary from region to region and applicator to applicator. Pipe diameter and wall thickness can play a role because most specifications call for increased polyolefinthickness as pipe diameter goes up – see Figure 4.
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