Coupling with Carbon Steel

Often the use of stainless-steel reinforcement is hmited to the outer part of the structure (skin reinforcement) or to its most critical parts for economical reasons. Furthermore, when stainless-steel bars are used in the rehabihtation of corroding structures, they are usually connected to the original carbon-steel rebars. Concern has been expressed with regard to the risk of galvanic corrosion of carbon steel induced by coupHng with stainless-steel bars. Actually, the galvanic corrosion that can arise when stainless steel is used in partial substitution of carbon steel has to be compared with that which takes place in the absence of stainless steels [30]. 

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Fracture fixation devices that are fabricated from stainless steel are unsuitable for coating or coupling with carbon because of galvanic effects (Haubold et ai, 1986). Carbon composite devices have been used reportedly with good results but such usage has not become widespread presumably because of an unaccepted cost/benefit ratio. 

Other test solutions (e.g.. Solution B) are also available to represent mild environments. Test temperature is normally 77°F (25°C), since tests have shown this temperature to be in the most severe range for hydrogen embrittlement effects. Test durations of 21-30 days are consistent with the observed rapid failure of susceptible materials. In testing CRA, the test specimen is commonly coupled to carbon steel to provide a severe hydrogen absorption condition. 

Naphthalene (qv) from coal tar continued to be the feedstock of choice ia both the United States and Germany until the late 1950s, when a shortage of naphthalene coupled with the availabihty of xylenes from a burgeoning petrochemical industry forced many companies to use o-xylene [95-47-6] (8). Air oxidation of 90% pure o-xylene to phthaUc anhydride was commercialized ia 1946 (9,10). An advantage of o-xylene is the theoretical yield to phthaUc anhydride of 1.395 kg/kg. With naphthalene, two of the ten carbon atoms are lost to carbon oxide formation and at most a 1.157-kg/kg yield is possible. Although both are suitable feedstocks, o-xylene is overwhelmingly favored. Coal-tar naphthalene is used ia some cases, eg, where it is readily available from coke operations ia steel mills (see Steel). Naphthalene can be produced by hydrodealkylation of substituted naphthalenes from refinery operations (8), but no refinery-produced napthalene is used as feedstock. Alkyl naphthalenes can be converted directiy to phthaUc anhydride, but at low yields (11,12). 

Recommended materials are outlined in the standards. Some of the recommendations in the standard are carbon steel for base plates, heat-treated forged steel for compressor wheels, heat-treated forged alloy steel for turbine wheels, and forged steel for couplings. The growth of materials technology has been so rapid especially in the area of high temperature materials the standard does not deal with it. Details of some of the materials... 

The ferritic steel 430S17 has enhanced oxidation resistance and finds some applications in sheet form, but its strength at elevated temperature is low. The higher chromium (20-30%) ferritic types show excellent oxidation resistance, but have poor elevated-temperature strength and, being difficult to produce and fabricate, are not used in large quantity. Cast versions of 27-30% Cr are quite widely used, especially where oxidation resistance, coupled with abrasion resistance, is required when high carbon contents are utilised. Such alloys are brittle. 

Access of air and water will also affect the corrosion rate. Metal inserts in corrosive plastics are most actively attacked at the plastic/metal/air interfaces with certain metals, notably aluminium titaniumand stainless steel, crevice effects (oxygen shielding and entrapment of water) frequently accelerate attack. Acceleration of corrosion by bimetallic couples between carbon-fibre-reinforced plastics and metals presents a problem in the use of these composites. 

Oxygen infiltration coupled with (steam volatile) carbon dioxide produces enhanced condensate line corrosion. The corrosion rate of steel in the system is particularly high when both gases are present. 

As reported by Steel et al. three structural isomers of bis(camphor-pyrazol-l-yl)methane (21a, 21b and 21c) are formed by coupling of camphorpyrazole 10 [i.e., (4S,7i )-7,8,8-trimethyl-4,5,6,7-tetrahydro-4,7-methano-l(2)H-indazole] with CH2CI2 (121). Isomer 21c can be separated from the other two structural isomers by crystallization or column chomatography. Deprotonation at the bridging carbon atom, subsequent reaction with carbon dioxide and acidic workup yields the enantiopure bis(camphorpyrazol-l-yl)acetic acid Hbpa (8) (Scheme 17, Fig. 19) (116). Due to missing substituents at the p5rrazolyl carbon C5 and a hence likely ortho metallation, isomers 21a and 21b are not suited for his reaction (72). 

As mentioned above, the environment has a significant effect on whether or not galvanic corrosion will be a problem. For example, carbon steel will corrode rapidly if equal or larger areas of Monel 400 are coupled with it in seawater. Conversely, carbon steel is compatible with Monel 400 in concentrated caustic solutions. Even freshwater can be sufficiently different from seawater couples incompatible in seawater work well in freshwater. For example, copper-steel and aluminum-steet couples are satisfactory for handling... 

Uniform corrosion usually occurs in fairly aggressive environments that attack the whole surface. Examples include carbon steel in seawater or acids, or aluminum alloys in strong alkali. The rate of metal loss is usually rather high, but, because it is distributed over the whole surface, the performance can usually be predicted, and managed with corrosion allowances, in most situations. Thus, sheet steel piling is often used in seawater without any corrosion protection, the corrosion rate of around 0.1 mm/yr, coupled with the relatively thick steel sections, giving an acceptable life. 

Fio. 9.3.4 Excitation with a surface coil of 9 mm diameter in a Bo gradient of the order of lOT/m by the NMR-MOUSE (a) Series train of CPMG echoes from a carbon-black filled SBR section of an intact car tyre with a steel belt. A fit of the echo envelope with an exponential decay function yields a transverse relaxation time Ti [Eidl]. (b) Variation of the pulse duration in an a — te/l — Ta — ts/ i- pulse sequence for different rf frequencies. For each frequency maxima and minima are observed which define the nominal 90° and 180° pulse widths. With decreasing rf frequency the distance of the sensitive volume from the rf coil increases. A frequency of 17.5 MHz correspond to depths of 0-0.5 mm, 16MHz to 0.5-1.0mm, and 16.5 MHz to 1.0-1.5 mm into the sample [Gut3], (c) Hahn- and solid-echo envelopes for a sample of carbon-black filled cross-linked SBR. The Hahn-echo decay is faster because of residual dipolar couplings which are partially refocused by the solid-echo [Gut3]. (d) Multi-echo excitation. 

Silicon bronzes are alloyed principally with silicon to achieve high strength, similar to carbon steel, coupled with good toughness and excellent corrosion resistance. Applications include fasteners, pumps and bearings. 

A battery of complementary techniques is often necessary (and always desirable) to provide reliable, applications-oriented characterization of the bulk properties of (catalytic) carbon materials. Arguably the most useful ones are transmission electron microscopy (TEM), thermoelectric power (TEP) measurements, electron spin resonance (ESR) spectroscopy coupled with a superconducting quantum interference device (SQUID), and Raman spectroscopy. For example, among the recently reported virtues of Raman spectroscopy is the identification of graphite whiskers [152,153] in three carbonaceous chondrite meteorites (M. Fries and A. Steele, Science Online, Feb. 28, 2008), which contain some of the oldest matter in the solar system and has thus generated tremendous interest among astrophysicists. 

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