Structures corrosive environments

Non-metallic impurities in liquid alkali metals play a major role in the corrosion of materials either by affecting metal solubilities, f orming spalli-ble corrosion products on the metal surface, promoting liquid metal embrittlement or bulk embrittlement of the surface or by sensitising the structure for further attack by other impurities e.g. O2. As in other corrosive environments the direction and magnitude of these impurity reactions... 

A metal s resistance to fatigue is markedly reduced in a corrosive environment. Many welded structures are subjected to fluctuating stresses which, with the superimposed tensile residual stress of the joint, can be dangerous. In addition to this a welded joint is a discontinuity in an engineering structure containing many possible sites of stress concentration, e.g. toe or root of the joint, weld ripple. 

In short, the current demand for cathodic protection varies according to the aggressiveness of the corrosive environment. It is for this reason that cathodic protection finds its greatest application where the pH is close to neutral. The more acid environments entail a current output that rapidly becomes uneconomic. The more alkaline environments prove less aggressive to the structure and therefore often do not justify cathodic protection. Table 10.5 provides some estimated current densities for cathodic protection that illustrate the point. 

It has been noted that the total current required to protect large structures can be substantial even in mildly corrosive environments. In seawater, for example, an initial current in the region of 200mA/m for bare steel might well be required in the North Sea. This is because the relatively high oxygen concentration and the tide and wave action all contribute to a facile cathodic reaction. Fortunately this current diminishes with time. The reason for this is the protective scale on the steel surface which forms during cathodic protection by decomposition of the seawater. 

Reinforced concrete structures that are fully immersed or buried in a corrosive environment may generally be protected using conventional cathodic... 

Applications. CVD ceramic powders such as SiC and Si3N4 are used to produce ceramic bodies for a wide variety of applications, either experimentally or in production. These include structural applications in high temperature or corrosive environments where metals are not suitable, in such areas as reciprocating engines, gas turbines, turbochargers, bearings, machinery, and process equipment. 

The interaction in an interface of device/tissue is limited by two factors. There is the corrosive environment, such as biological fluid, which contains salts and proteins among other cellular structures in which the sensor device must survive [47, 48], Second, there is the encapsulation material which may induce a toxic reaction due to poor biocompatibility and hemocompatibility [49, 50], It is crucial to use a biomaterial that can overcome both limiting factors to maintain the lifetime of the sensor device and protect the body [51, 52],... 

Adhesives and sealers can be an important part of a total corrosion protection system. Structural bonding procedures and adhesives for aluminum, polymer composites, and titanium are well established in the aerospace industry. Structural bonding of steel is gaining increasing prominence in the appliance and automotive industries. The durability of adhesive bonds has been discussed by a number of authors (see, e.g., 85). The effects of aggressive environments on adhesive bonds are of particular concern. Minford ( ) has presented a comparative evaluation of aluminum joints in salt water exposure Smith ( ) has discussed steel-epoxy bond endurance under hydrothermal stress Drain et al. (8 ) and Dodiuk et al. (8 ) have presented results on the effects of water on performance of various adhesive/substrate combinations. In this volume, the durability of adhesive bonds in the presence of water and in corrosive environments is discussed by Matienzo et al., Gosselin, and Holubka et al. The effects of aggressive environments on adhesively bonded steel structures have a number of features in common with their effects on coated steel, but the mechanical requirements placed on adhesive bonds add an additional level of complication. 

Very pure single crystals have defects that can effect corrosion, but impurities and alloying elements, grain boundaries, second phases, and inclusions often have serious effects. Welded structures invariably corrode first at the welds because of metallurgical heterogeneities that exist in and near welds. The most susceptible site or defect in a metal will be the first to be attacked on exposure to a corrosive environment. Sometimes such attack simply results in innocuous removal of the susceptible material, leaving a surface with improved corrosion resistance. (Frankel)5... 

Plastics are often used in corrosive environments for chemical tanks, water treatment plants, and piping to handle drainage, sewage, and water supply. Structural shapes for use under corrosive conditions often take advantage of the properties of RPs. Today s underground tanks must last thirty or more years without undue maintenance. To meet these criteria they must be able to maintain their structural integrity and... 

Any unit, structure, or component that is subject to vibration, or any other fluctuating stress in presence of a corrosive environment. 

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