Corrosion system, definition

The first three items have been discussed to some extent in the related literatm-e somewhere else [16, 17, 18]. However, it is worth it to concentrate more on the last item, t.e., corrosion system definition. 

Terminology The International Standards Organization has recently defined a corrosion inhibitor as a chemical substance which decreases the corrosion rate when present in the corrosion system at a suitable concentration, without significantly changing the concentration of any other corrosive agent. This last point is significant since it excludes chemicals employed for deaeration or pH control from the definition of a corrosion inhibitor. On the other hand, it should be noted that the inhibitor is .. . present in the corrosion system. . . , and thus arsenic when added to brasses to prevent dezin-cihcation may be classified as an inhibitor. 

The environmental boundaries of a liquid metal system are set by the containment material. This material may experience other types of corrosion on the exterior surface (of pipe or tubing for example), but it isolates the liquid metal from interaction with any external atmosphere. This specification of "contained and isolated" sets the limits for the liquid metal corrosion system. Other more genercJ areas of liquid metal/metal interaction, such as that produced when, for example, liquid steel or aluminum come into contact with materials employed in their production, are excluded by this definition. Liquid metal embrittlement will not be addressed. Information on this topic can be found elsewhere [1-3]. 

The addition of small amounts of chemicals capable of reducing corrosion of the exposed metal is a preventative measure known as corrosion inhibition. According to the ISO 8044 definition, corrosion inhibitors are chemical substances, which decrease the corrosion rate, when present in the corrosion system in sufficient concentration, without significantly changing the concentration of any other corrosive agents. 

Modem three layers pressure vessels are under study, which consist of a stressbearing component - an inner polymer liner over-wrapped with a carbon-fibre composite - and an outer aramid-material layer, mechanical and corrosion damage resistant [1]. A system for the gaseous hydrogen storage at room temperature has also been designed, adopting a definite number of linked cylindrical pressure vessels [13]. 

This behavior is characterized by a plateau region, which prevails above a definite threshold K. It is often referred to as stress-corrosion fatigue because SCC systems usually exhibit this behavior, and the most common theory assumes that the crack growth rate results from the addition of SCC, and pure fatigue crack advance. This is a type of... 

It follows that if a corrosive environment is present, it seems unlikely to be physically prevented from reaching the surface of the substrate. DeLaat reported cases of serious corrosion with bonded films, although in some at least of these the films had not been properly used. On the other hand, Peterson and Finkin carried out a very thorough survey of US Naval Air Rework Facilities in 1970-71. At that time the system would certainly have still included coatings of older formulations, without improved corrosion inhibition, but they found very few definite cases of corrosion, and in several of those the use of bonded films was probably not responsible. 

Chemicals and chemical mixtures that attack the respiratory system are categorized as corrosives, irritants, and sensitizers. Though the term irritant is often applied in the literature to chemicals that are either corrosives or irritants, the definitions used here are those that follow. These definitions are identical to those used by toxicologists and regulatory agencies to classify the hazards due to chemical inhalation. 

The literature is not entirely consistent as to the definition of high and low pressure. However, at pressures above 6000 bar the question of material choice (particularly if corrosive fluids are to be employed in the system) becomes critical and a specialized reactor design must be chosen [17,18]. As such, this discussion focuses on systems designed for use at pressures below 6000 bar. 

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