Methods of Prevention

Five methods for prevention or minimization of damage due to erosion-corrosion are used. In order of importance they are  

Stress corrosion cracking (SCC) refers to cracking caused by the simultaneous presence of tensile stress and a specific corrosive medium. 

Cross sections of SCC frequently show branched cracks. This river branching pattern is unique to SCC and is used in failure analysis to identify when this form of corrosion has occurred. 

This cracking phenomenon has serious consequences since it can occur at stresses within the range of a typical design. 

The two classic cases of stress-corrosion cracking are the season cracking of brass, and the caustic embrittlement of steel. Both of these obsolete terms describe the environmental conditions 

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The second approach, changing the environment, is a widely used, practical method of preventing corrosion. In aqueous systems, there are three ways to effect a change in environment to inhibit corrosion (/) form a protective film of calcium carbonate on the metal surface using the natural calcium and alkalinity in the water, (2) remove the corrosive oxygen from the water, either by mechanical or chemical deaeration, and (3) add corrosion inhibitors. 

Methods of preventing hydrate formation include adding heat to assure that the temperature is always above the hydrate formation temperature, lowering the hydrate formation temperature with chemical inhibition, or dehydrating the gas so that water vapor will not condense into free water. It is also feasible to design the process so that if hydrates form they can be melted before they plug equipment. 

The American Institute of Chemical Engineers (AIChE) has been involved with process safety and loss control for chemical and petrochemical plants for more than thirty years. Through its strong ties with process designers, builders, operators, safety professionals, and academia, AIChE has enhanced communication and fostered improvements in the safety standards of the industry. Its publications and symposia on causes of accidents and methods of prevention have become information resources for the chemical engineering profession. 

One of the most effective methods of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service. Once the conditions of service and environment have been determined that the equipment must withstand, there are several materials available commercially that can be selected to perform an effective service in a compatible environment. Some of the major problems arise from popular misconceptions for example, the use of stainless steel. Stainless steel is not stainless and is not the most corrosion-resistant material. Compatibility of material with service environment is therefore essential. For example, in a hydrogen sulfide environment, high-strength alloys (i.e., yield strength above 90,000 psi or Rc 20 to 22) should be avoided. In material selection some factors that are important to consider are material s physical and chemical properties, economics and availability. 

These materials are designed to reduce water from condensation dripping on equipment, etc. They often incorporate particles of cork so that water is absorbed. They are generally thick films to provide some insulation and have a rough textured surface finish to increase the surface area and encourage water evaporation. In general, physical methods of prevention such as adequate ventilation, etc. are more effective. 

Two methods of preventing overheating are available either general ventilation to provide fairly even conditions over the whole space at working level or local ventilation to give spot cooling for localized hot spots. 

Prevention Methods of prevention already summarised may be used singly or in combination. Elimination of sulphur and certain of its compounds are most effective but more recently more resistant materials such as polythene or asbestos are used to replace iron and concrete where acid corrosion in severe. 

Edwards, A. M., Proc. Symp. on Developments in Methods of Prevention and Control of Corrosion in Buildings, British Iron and Steel Federation, London (1966)... 

Fig. 9.6 Method of preventing corrosion by premature condensation of acidic vapours. pH measured continuously at point X automatically controls flow of sodium hydroxide...

The results of development work on processes indicate that the two main methods of preventing the duplex microstructure from forming appear to be fast-firing, or increasing the amount of / "-alumina at low temperatures. Based on these results, Duncan et al. [20] and Zyl et al. [21] have described production processes starting from aluminum oxy-hydroxides or aluminum hydroxides as precursors for the synthesis of the solid electrolyte "-alumina. Duncan et al. described an alumina precursor which substitutes in part or wholly for or-alumina in an established... 

M. D. Clark, P. L. Walker, K. L. Schreiner, and P. D. Nguyen. Methods of preventing well fracture proppant flow-back. Patent US 6116342, 2000. 

S. E. Lindow, Methods of preventing frost injury caused by epiphytic ice-nucle-ation-active bacteria. Plant Disease March ill (1983). 

Combinations of antiemetics may be the most effective method of preventing PONV for high-risk patients.7,42 Droperidol plus a 5-HT3 antagonist or dexamethasone plus a 5-HT3 antagonist are effective combinations.43,44 Three-drug combinations such as dexamethasone, droperidol, and a 5-HT3 antagonist have not been formally studied but may be a reasonable approach.42... 

Risky foods include tap water uncooked foods, including seafood, fruits, and vegetables and foods that are stored inadequately, particularly buffet-style meals. Additionally, alcohol consumption of more than five drinks per day has been demonstrated to be a risk factor, especially in males.30 Education about the types of foods to avoid during travel can be an effective method of prevention. 

Schweigert, M.K., Mackenzie, D.P., and Sarlo, K., Occupational asthma and allergy associated with the use of enzymes in the detergent industry a review of the epidemiology, toxicology and methods of prevention, Clin Exp Allergy, 30, 1511, 2000. 

Removal of FMOC-OH can be achieved by liquid-liquid extraction (normally into pentane).A more elegant method of preventing interference of FMOC-OH is to react excess FMOC with a very hydrophobic amine (e.g. I -aminoadamantane) to form a derivative which elutes after the peaks of interest. 

Bowie, C. R, 1918, Oil-Storage Tanks and Reservoirs with a Brief Discussion of Losses of Oil in Storage and Methods of Prevention U.S. Bureau of Mines Bulletin No. 155, Petroleum Technology Report No. 41, 76 pp. 

Possible change in the sample Examples of methods of prevention... 

The causes of furnace blasts occurring in soda-regeneration plants when water is spilt into molten sodium carbonate, sodium chloride, sodium hydroxide, sodium sulfate or sodium sulfide are discussed, together with methods of prevention. 

Cathodic protection is another method of preventing rusting, as shown in Figure 11.29. As in galvanizing, a more reactive metal is attached to the iron object. This reactive metal acts as a sacrificial anode, and the iron becomes the cathode of a galvanic cell. Unlike galvanizing, the metal used in cathodic protection does not completely cover the iron. Because the sacrificial anode is slowly destroyed by oxidation, it must be replaced periodically. 

Nelson, H. W. (1973). A new theory to explain physical explosions. Tappi 56(3), 123. Nelson, H. W. (1978). Method of preventing explosions using a smelt water explosion inhibitor. U.S. Patent 4,106,978. 

Increased awareness of medication errors and methods of prevention throughout the health care system... 

A selective method of preventing the expression of adhesion molecules or cytokines is the use of antisense oligonucleotides. These oligonucleotides are short sequences of nucleic acids complementary to mRNA sequences of specific proteins of interest. If delivered to the cytoplasmic compartment of cells these oligonucleotides are able to form a complex with their target mRNA. In this way the translation of mRNA into protein by ribosomes is inhibited. The subsequent mRNA degradation by RNAse H results in reduced expression of the protein (see also Chapter 5 for a description of antisense ohgonucleotides as therapeutic modalities). 

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