Corrosion consequences

Metals and alloys do not respond alike to aU the influences of the many factors that are involved in corrosion. Consequently, it is impractical to establish any universal standard laboratoiy procedures for corrosion testing except for inspection tests. However, some details of laboratory testing need careful attention in order to achieve useful results. 

Oxygen is soluble in water to the extent of 9.4 ppm from air at 100 kPa and 20 °C, and 02 is the oxidant responsible for most metallic corrosion. Consequently, deaeration of water by purging with nitrogen or vacuum degassing may be desirable in some circumstances this should not be undertaken without circumspection, since deoxygenation may cause activation of otherwise passive metals or cause cathodic areas to become anodic (Chapter 16). At high temperatures, aqueous oxygen is consumed quite rapidly by hydrazine or sodium sulfite (Section 16.7). 

The advantages of a cationic adhesive formulation over that of a free radical one are the lack of oxygen sensitivity, less shrinkage on curing, and better adhesion. The disadvantages are that the photoinitiators are sensitive to moisture and basic materials and that the addic species can promote corrosion. Consequently, the majority of UV formulations used in industry are acrylate based and cured by a free radical mechanism. 

As discussed in previous chapters, there are many variables that affect atmospheric corrosion. Consequently, programs designed to study atmospheric corrosion have placed emphasis on standardization regarding test procedures. Several corrosion testing standards have been developed by the International Organization for Standardization (ISO) as follows ... 

Corrosion occurrence has been widely experienced in the oil and gas industry. In the following, the main corrosion processes in oil and gas phases are discussed. First of all it must be emphasized that corrosion is likely to occur only in the water phase, as the oil phase is considered non-corrosive. Consequently, the presence of free water is necessary for corrosion to occur, i.e. vaporized water in streams at temperatures above the dew point are considered non-corrosive. In addition, it is necessary, especially for mixed-phase streams (oil -i- gas -i- water) to verify the water wetting of materials if water is confined in the middle of the stream, or trapped by oil, no corrosion attack may develop. The principle factors controlling corrosion are ... 

Localized corrosion is far more treacherous in nature and far less readily predictable and controllable tlian unifonn corrosion and it is, moreover, capable of leading to unexpected damage witli disastrous consequences, especially since inspection of corrosion damage is in many cases difficult. 

The industrial value of furfuryl alcohol is a consequence of its low viscosity, high reactivity, and the outstanding chemical, mechanical, and thermal properties of its polymers, corrosion resistance, nonburning, low smoke emission, and exceUent char formation. The reactivity profile of furfuryl alcohol and resins is such that final curing can take place at ambient temperature with strong acids or at elevated temperature with latent acids. Major markets for furfuryl alcohol resins include the production of cores and molds for casting metals, corrosion-resistant fiber-reinforced plastics (FRPs), binders for refractories and corrosion-resistant cements and mortars. 

SiHcon nitride (see Nitrides) is a key material for stmctural ceramic appHcations in environments of high mechanical and thermal stress such as in vehicular propulsion engines. Properties which make this material uniquely suitable are high mechanical strength at room and elevated temperatures, good oxidation and creep resistance at high temperatures, high thermal shock resistance, exceUent abrasion and corrosion resistance, low density, and, consequently, a low moment of inertia. Additionally, siHcon nitride is made from abundant raw materials. 

Various patents (22—24) have been issued claiming the use of tetrakis(hydroxymethyl)phosphonium sulfate in, for example, water treating, pharmaceuticals (qv), and in the oil industry where this compound shows exceptional activity toward the sulfate-reducing bacteria that are a primary cause of hydrogen sulfide formation and consequent problems associated with souring and corrosion (25). 

ALkylamines are corrosive to copper, copper-containing alloys (brass), aluminum, 2inc, 2inc alloy, and galvani2ed surfaces. Aqueous solutions of aLkylamines slowly etch glass as a consequence of the basic properties of the amines in water. Carbon or stainless steel vessels and piping have been used satisfactorily for handling aLkylamines and, as noted above, some aLkylamines can act as corrosion inhibitors in boiler appHcations. 

Most of them are generally classified as poisons. Exceptions to this rule are known. A notable one is 4-dimethyl aminopyridine (DMAP) (24), which is widely used in industry as a superior acylation catalyst (27). Quaternary salts of pyridines are usually toxic, and in particular paraquat (20) exposure can have fatal consequences. Some chloropyridines, especially polychlorinated ones, should be handled with extra care because of their potential mutagenic effects. Vinylpyridines are corrosive to the skin, and can act as a sensitizer for some susceptible individuals. Niacin (27), niacinamide (26), and some pyridinecarbaldehydes can cause skin flushing. 

The corrosion resistance imparted to tantalum by the passivating surface thermal oxide layer makes the metal inert to most ha2ards associated with metals. Tantalum is noncorrosive in biological systems and consequently has a no chronic health ha2ard MSDS rating. 

The processiag costs associated with separation and corrosion are stiU significant ia the low pressure process for the process to be economical, the efficiency of recovery and recycle of the rhodium must be very high. Consequently, researchers have continued to seek new ways to faciUtate the separation and confine the corrosion. Extensive research was done with rhodium phosphine complexes bonded to soHd supports, but the resulting catalysts were not sufficiently stable, as rhodium was leached iato the product solution (27,28). A mote successful solution to the engineering problem resulted from the apphcation of a two-phase Hquid-Hquid process (29). The catalyst is synthesized with polar -SO Na groups on the phenyl rings of the triphenylphosphine. 

Compound (1) decomposes to form dichloroacetyl chloride, which in the presence of water decomposes to dichloroacetic acid and hydrochloric acid (HCl) with consequent increases in the corrosive action of the solvent on metal surfaces. Compound (2) decomposes to yield phosgene, carbon monoxide, and hydrogen chloride with an increase in the corrosive action on metal surfaces. 

For many years the usual procedure in plant design was to identify the hazards, by one of the systematic techniques described later or by waiting until an accident occurred, and then add on protec tive equipment to control future accidents or protect people from their consequences. This protective equipment is often complex and expensive and requires regular testing and maintenance. It often interferes with the smooth operation of the plant and is sometimes bypassed. Gradually the industry came to resize that, whenever possible, one should design user-friendly plants which can withstand human error and equipment failure without serious effects on safety (and output and emciency). When we handle flammable, explosive, toxic, or corrosive materials we can tolerate only very low failure rates, of people and equipment—rates which it may be impossible or impracticable to achieve consistently for long periods of time. 

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