Nonmetallic materials, corrosion

Recommended practice for applying statistics to analysis of corrosion data Practice for operating light- and water-exposure apparatus (carbon-arc Type) for exposure of nonmetallic materials Method for detecting susceptibility to intergranular attack in wrought nickel-rich, chromium-bearing alloys... 

Nomnetallics As stated, corrosion of metals apphes specifically to chemical or electrochemical attack. The deterioration of plastics and other nonmetallic materials, which are susceptible to sweUing crazing, cracking, softening, and so on, is essentially physiochemical rather than electrochemical in nature. Nonmetallic materials can either be rapidly deteriorated when exposed to a particular enviromnent or, at the other extreme, be practicidly unaffected. Under some conditions, a nonmetallic may show evidence of gradual deterioration. However, it is seldom possible to evaluate its chemical resistance by measurements of weight loss alone, as is most generally done for metals. 

Crevice Corrosion Crevice corrosion occurs within or adjacent to a crevice formed by contact with another piece of the same or another metal or with a nonmetallic material. When this occurs, the intensity of attack is usually more severe than on surrounding areas of the same surface. 

Paralleling the corrosion problem is one involving compatibility of any well fluid with nonmetallic materials used in well completion apparatus. All injection wells and many producing wells are equipped with packers to isolate the casing annulus from the high temperature, pressure, and salinity characteristic of the petroleum reservoir environment. Conventional packers, as well as other well tools, utilize elastomeric materials to mechanically seal appropriate locations. 

Thermal transmission testing is an excellent way of detecting various types of anomalies such as surface corrosion under paint before the corrosion becomes visually evident. Thin, single-layer structures, such as aircraft skin panels, can be inspected for surface and subsurface discontinuities. This test is simple and inexpensive, although materials with poor heat-transfer properties are difficult to test, and the joint must be accessible from both sides. For nonmetallic materials, the defect diameter must be on the order of 4 times its depth below the surface to obtain a reliable thermal indication. For metals, the defect diameter must be approximately 8 times its depth. Some bright surfaces such as bare copper and aluminum do not emit sufficient infrared radiation and may require a darkening coating on their surface. 

RO permeate distribution piping considerations need to be mindful of the fact that the permeate is highly corrosive. Retrofitting an RO system into a facility with carbon steel permeate piping is difficult, as the piping will corrode. Nonmetallic materials such as plastics and fiberglass are recommended for low-pressure RO product distribution piping. 

Ceramic Ceramics are nonmetallic materials that have been created under intense heat. Ceramics tend to be extremely hard, heat-resistant and corrosion-resistant. They are generally poor conductors of temperature changes or electricity. Ceramics are used in low-tech and high-tech applications, ranging from the insulators in spark plugs to the heat shield on the Space Shuttle. 

The miscellaneous materials committees include paint, paper, packaging, rubber textiles, and plastics. The miscellaneous subjects committees include emission spectroscopy, fire standards, appearance of materials, microscopy, and resource recovery. The materials for specific applications committees include electronics, tires, consumer products, and food-service equipment. The corrosion, deterioration, and degradation of materials committees include corrosion of metals, erosion and wear, and durability of nonmetallic materials. 

The term corrosion may also be applied to nonmetals, and these are touched on in this article, but the chemistry in this case will be different, and the wide variety of nonmetallic materials precludes detailed coverage here. 

Corrosion tests have inevitable limitations in their capacities to mimic actual service conditions of equipment. Standard, ambient pressure, immersion test procedures, with intermittent fluid refreshment, are available for both metallic and nonmetallic materials, but are limited to the ambient pressure boiling point of the fluid, and provide limited scope to simulate the effects of stress, geometry, heat transfer, and fluid flow. Such fesf procedures can be conducted at plant pressures and temperatures in autoclaves, and can be upgraded to focus on specific factors such as fluid flow and heat transfer. Even so a laboratory test, however elaborate, is a poor substitute for a test in the plant itself. 

In modem technology an increasing number of nonmetallic materials, such as semiconductors, oxides, ionic crystals, and polymers, is employed, which corrode or degrade via chemical rather than electrochemical mechanisms. Corrosion protection of these materials by inhibitors is currently only marginally studied and will be an important future challenge for inhibitor science. For the important case of oxides, similar concepts as employed for the stabilization of passive films in the inhibition of localized corrosion should be applicable. 

Chemical plants are designed and constructed with a variety of metals, alloys, and nonmetallic materials such as plastics. The nature and mechanism of degradation of these materials differ. Corrosion of metals and alloys in aqueous media occurs by electrochemical mechanisms, whereas the degradation of a plastic is by the penetration of chemicals into its matrix. Nevertheless, the term corrosion is used liberally to describe the oxidation of metals in aqueous solutions or gas phases and the deterioration of plastics by chemical attack. 

Bleach plant corrosion testing has included corrosion coupon testing, electrochemical testing, electrochemical protection testing, and nonmetallic materials evaluation. Coupon exposure tests have been used to rank candidate materials for these applications. Nonmetallic materials including thermoplastics, thermosets, brick, and tile are widely used in the bleach plant. 

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