Corrosive elements

The ash analysis receives special attention because of certain trace metals in the ash that cause corrosion. Elements of prime concern are vanadium, sodium, potassium, lead, and calcium. The first four are restricted because of their contribution to corrosion at elevated temperatures however, all these elements may leave deposits on the blading. 

Specifically note that Type 7 (explosion-proof) enclosures and their associated conduit systems are neither gas or liquid tight. Consequently, corrosive gases such as hydrogen sulfide and water from rain or internal condensation can accumulate with the enclosure. Premature failure of electrical devices and interconnections often results when preventive measures such as drains, air purges, and dual rated enclosures are not used to remove or exclude these corrosive elements. Type 7 enclosures are intended for indoor use. 

Too much enphasis has be given to adhesion under dry conditions. However, corrosion is only possible if enough water is present in the ooating/metal interface to provide the electrolyte for the corrosion elements to operate. This condition is hardly imaginable without a previous significant reduction or even the loss of adhesion. Therefore "wet adhesion" is considered to be of crucial inportance to corrosion protection by organic coatings (9). 

The other major springboard for the fluorocarbon chemical industry was the "Manhattan Project to develop the atomic bomb. This required the large-scale production of highly corrosive elemental fluorine and uranium(VI) fluoride for the separation of the radioactive 235U isotope. Oils capable of resisting these materials were needed to lubricate pumps and compressors, and polymers were needed to provide seals. Peril uorinated alkanes and polymers such as PTFE and poly(chlorotrifluoroethylene) (PCTFE) proved to have the appropriate properties so practical processes had to be developed for production in the quantities required. In 1947 much of this work was declassified and was published in an extensive series of papers3 which described the fundamental chemistry on which the commercial development of various fluoro-organic products, especially fine chemicals, was subsequently based. 

Use Corrosion Resistant Materials. Some of the sludge generated is the result of corrosion or deterioration of the storage tank internals. Installation of a liner or using materials of construction which are more resistant to the corrosive elements of crude oil reduces sludge production. 

The humble deaerator, operated by the Utility Department, is an interesting and important component of any process facility. Oxygen is a highly corrosive element, and if left in the boiler feedwater, would rapidly oxidize the boiler s tubes. 

Another method which has been used for removing corrosive elements from the reactor effluent is bauxite treatment. The effluent hydrocarbons are heated and passed through the bauxite, which is usually located on the deisobutanizer feed, and the bauxite breaks down the corrosive sulfur compounds and retains them. 

NACE studies determined that the most severe corrosion problems occurred under thermal insulation at temperatures between 140° and 250° F (60° to 120° C) where the temperatures were too low to quickly boil off any intruding water. At temperatures higher than the boiling point of water, other corrosion problems can occur. The intruding water can carry chlorides and other corrosive elements that can concentrate and result in stress corrosion cracking. [15]... 

Higher-valent metal halides oxidize diaryl tellurium compounds to diaryl tellurium dihalides. Copper(II) halides can be generated in the reaction mixture from easily accessible copper(II) acetate and hydrohalic acids4. These halogenation reactions are convenient alternatives to the methods using corrosive elemental halogens or sulfuryl halides. 

A 3-mm hole developed at the bottom of an oil storage tank after 25 months of service. This premature failure of the tank raised questions as to the construction material of the tank as well as the possibility of corrosive elements (i.e., water) present in the contents of the tank. 

The filter material is easy accessible and cheap to replace, insensitive to hot particles, temperature fluctuations and corrosive elements in the flue gas. 

Review with the owner his operating procedure, include corrosive elements anticipated query him in detail. Determine low and high temperatures anticipated and their duration. Thermal shock is or may be an important factor. Review the type of cleaning to be used, water-hot, cold, steaming. The type of cleaning agents and solutions or solvents can be a factor. 

One attractive and distinctive feature of wood is that it is a readily renewable resource. It has a very low ash content and is free of sulphur and other obviously polluting or corrosive elements. In almost all other respects the characteristies of wood are less desirable than alternative fuels ... 

This removal was also reflected in the retained ash. Although silicon and aluminum were removed from the coal, their percentage concentrations in the treated ash did not differ significantly from that of the untreated coal. It is important to note that the more corrosive elements, the alkalis and alkaline earths, appear to be particularly responsive to this treatment. 

Millions of dollars are spent annually in an attempt to correct the damage resulting from corrosion. A current area of chemical research is concerned with the development of corrosion-inhibiting processes. In one type of corrosion, elemental iron is oxidized to iron(III) oxide (rust) ... 

Under certain conditions it is possible to melt small quantities of metals, alloys and related compoimds in such a way that they do not make or barely make contact with the wall of the container. Such a procedure becomes veiy desirable when one deals with corrosive elements or when products of very high purity are required. However, containerless fusion is possible only in special cases. For example, the sample may be heated to melting by means of an electric arc or a directional electron beam in this case the sample rests in a shallow depression in a cooled copper plate. The molten sample contracts due to surface tension to form an oblate spheroid whose area of contact with the copper support is so small that no contamination occurs during the short fusion process. The resolidified sample is turned over and remelted on the other side. This procedure is called button melting. For heat sources, see Part I, p. 42. 

In the case of the slightest defects in the coating corrosion elements appear on the metal substrate. As a result, areas of the substrate insulated by the coating from the corrosive medium function as the cathode and the naked areas of the substrate near the coating defects serve as the anode and acquire a more negative potential than the cathodic areas. The electrode potential difference between the anodic and cathodic areas of the substrate is a function of the ohmic potential drop on the cathode and can reach 200-300 mV. This is commensurate with the contact potential difference assumed dangerous for metal structures (0.25 V) [1]. 

Corrosion Thickness and composition of surface oxides Identification of corrosive elements (e.g.. Cl) Passivation layer composition and thickness... 

FIFE tape is used in many applications, including sealing joints, insulating conductive wires, and protecting materials from corrosive elements. FIFE demonstrates a good chemical and heat resistance, electrical insulation characteristics, as well as a low coefficient of friction. However, in general, it has less than desirable mechanical properties, in particular with respect to abrasion resistance and compression strength. 

A corroding metal snrface represents a collection of corrosion elements, with the constancy, the spread, and the attendant macroscopic interface of the anode and cathode surfaces depending on the system. The distribution of local anodic and cathode current densities and at the surface of an electrode can differ appreciably. Possibilities are = i, = +Ie, and = -is- The cur-... 

The corrosion behavior of metals cannot be predicted from the position of their standard potentials in the electrochemical series because the potential of an electrode changes with the current density. If an electrode in which only one electrode process takes place is termed a working electrode and the resultant potential, a working potential, then the differences between working potential and the Nernst equilibrium potential is called an overpotential, that is caused by reaction restraints. In general, polarization is defined as the shift in potential of working electrodes within a corrosion element. In such an element, at least two electrode reactions occur whose overpotentials are superimposed, resulting in the polarization effect. 

The cause of nonuniform corrosion is the presence of corrosion elements, that is, heterogeneous mixed electrodes. The common feature of both types of corrosion is the geometry of the damaged area. The surface spread of these areas is generally greater than the depth. Accordingly, compared with localized types of corrosion such as pitting, these types of corrosion are limited in extent. 

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