Stress metal

In general, the higher the residual or applied metal stress, the more severe the corrosion at a given acidic pH. This explains why many heat exchanger tube ends are often attacked so severely (Fig. 7.1). Tube ends that have been rolled or welded often contain high residual stress. Further, crevices are sometimes present in which acidic species may concentrate (see Chap. 2, Crevice Corrosion ). Screens, rolled sheet metal, and other highly worked metals (not stress relieved) are also prone to attack. 

The condition of the test metal is important. Clean metal samples with uniform finishes are preferred. The accelerating effects of surface defects lead to deceptive results in samples. The ratio of the area of a defect to the total surface area of the metal is much higlier in a sample than in any metal in service. This is an indication of the inaccuracy of tests made on metals with improper finishes. The sample metal should have the same type of heat treatment as the metal to be used in service. Different heat treatments have different effects on corrosion. Heat treatment may improve or reduce the corrosion resistance of a metal in an unpredictable manner. For the purpose of selectivity, a metal stress corrosion test may be performed. General trends of the performance of a material can be obtained from such tests however, it is difficult to reproduce the stress that actually will occur during service. 

The Reduction of the Pressure bv Depressuring - The reduction of pressure in a vessel exposed to fire has the advantages of not only reducing the metal stress to a value that will not result in failure, but also of reducing markedly the quantity of fuel that might feed the fire. 

Pressure can liave a significant impact on safety. Extreme pressures can cause severe metal stress, which can lead to a vessel rupture or explosion. High temperatures, plugged lines, and many other condiUons can cause increased pressure. 

Spannungs-freiglUhen, n. Metal.) stress-relief anneal, -grad, m. degree of tension, spannungslos, a. without tension or strain Elec.) dead. 

MAWP is calculated using nominal standard steel plates (but could be other metal—use code stresses) thickness, using maximum vessel operating temperature for metal stress determinations. See Ref [1] Par. UG-98. 

An important area of work utilizing TEM involves the study of metals and mietal oxides.. Explosively formed or fractured metals are of special interest using this technique (Refs 35 46), as are studies of metallic smoke particles (Ref 17) and metallic stress phenomena (Ref 34)... 

In these boilers, various interrelated, complex surface chemistry reactions may occur at the metal-water interface, which (apart from the development of a desirable protective magnetite film) can lead to the formation of unwanted deposits. These surface reactions are influenced by the specific heat flux, operating temperatures, and the areas and degree of local metal stress resulting within a particular boiler. 

NOTE Water hammer is caused by sudden interruptions in flow as when steam meets draining condensate. The steam produces instantaneous surges of pressurized water that hits valves, elbows, and tees at high velocity. This produces a hammering sound and leads to metal stress and possible failure. 

Instantaneous surges of water under pressure caused by sudden interruptions in water flow in a pipe or water system, producing a hammering sound and leading to metal stress and possible eventual failure. Water hammer can develop where a steam main is incorrectly pitched, has un-drained pockets or where steam flows up and meets draining condensate flowing down causing a temporary interruption in both flows. 

Jackson, P.J., Naranjo, C.M., McClure, P.R. Roth, E.J. (1985). The molecular response of cadmium resistant Datura innoxia cells to heavy metal stress. In Cellular and Molecular Biology of Plant Stress, ed. J.L. Key and T. Kosuge, pp. 145-60. New York Alan R. Liss. 

Microbes that lack a specific active transport system for removing toxic metals may be able to sequester heavy metals either inside or outside of the cell. Intracellular sequestration occurs when cytoplasmic metal-binding molecules are produced in response to metal stress, preventing the metals from interacting with vital cell structures. The two most common molecules used for intracellular... 

Mathew, P. and N.R. Menon. 1993. Heavy metal stress induced variations in 0 N ratio in two tropical bivalves Pema indica (Kuriakose Nair) and Donax incamatus Gmelin. Indian Jour. Exper. Biol. 31 694-698. 

Calabrese, A., J.R. Maclnnes, D.A. Nelson, and J.E. Miller. 1977. Survival and growth of bivalve larvae under heavy-metal stress. Mar. Biol. 41 179-184. 

Bringezu K, Lichtenberger O, Leopold I, Neumann D. Heavy metal stress of Silene vulgaris. J Plant Physiol 1999 154 536-546. 

A. halleri is found on sites with high levels of Zn, Cd and Pb, but while plants constitutively accumulate Zn and Cd, they do not accumulate Pb (Bert et al. 2002). Individuals from non-metallicolous (i.e., environments where there is no metal stress) populations have a higher capacity to hyper-accumulate than do plants adapted to contaminated sites. Among back-cross progenies from the hybrid A. halleri x A. lyrata, segregation was observed... 

Plants exposed to heavy metal stress often increase the pH of the growing medium in order to reduce their uptake. We have recorded such a response in Sinapis alba L cv. Nakielska plants grown in the presence of (Figure 5) (Wihska-Krysiak and Gawrohski, 2002). This parameter... 

Krupa, Z., Baranowska, M., and Orzol, D., Can anthocyanins be considered as heavy metal stress indicator in higher plants Acta Physiol Plant., 18, 147, 1996. 

Carbon deposits cause hot spots. A temperature gradient exists between the hot spot and the cooler adjacent metal. The result is high metal stress, distortion, and cracking. 

Kaye JZ, Baross JA (2002) Salinity, pressure, and heavy-metal stress response of moderately halophilic bacteria isolated from hydrothermal-vent environments. EOS 83 F1450... 

M. N. V. Prasad and J. Hagemeyer, Heavy Metal Stress in Plants, Springer-Verlag, Berlin, 1999, p. 356. 

Various mechanisms have been developed by plants to alleviate stress imposed by exposure to toxic metal concentrations. Although the biochemical and molecular bases of adaptation and resistance of plant communities to high metal levels will be discussed extensively in Chapter 3, a survey summarising the possible anti-metal stress defence strategies and mechanisms forms an essential part of this chapter on toxicology. Every plant species, whether it is resistant or not to high metal concentrations, possesses defence responses against increased metal concentrations in the cell indeed. 

Ahner, B.A., Wei, L., Oleson, J.R., and Ogura, N. (2002) Glutathione and other low molecular weight thiols in marine phytoplankton under metal stress. Mar. Ecol. Prog. Ser. 232, 93-103. 

Surface Instability and the Internal Decay of Metals Stress-Corrosion Cracking... 

Another form of corrosion is due in part to the mechanical forces applied to metals, stress corrosion. When the corrosion reaction occurs with hydrogen evolution, hydrogen atoms, owing to their small size, can enter the metallic lattice and thus reduce the strength of the interatomic bonds. This is known as hydrogen embrittlement. If afterwards we apply a mechanical stress to the metal there is a greater possibility that it will rupture. Corrosion fatigue can have similar effects. This has been held responsible for some aeroplane crashes. 

Coordination complexes in which the metal is coordinated by a bio-ligand present in a biological matrix (e.g., metal-binding peptides which are enzymatically synthesized in living organisms exposed to heavy metal stress). 

Suzuki and Banfield (1999) classify methods of microbial uranium accumulation as either metabolism dependent or metabolism independent. The former consists of precipitation or complexa-tion with metabohcally produced ligands, processes induced by active cellular pumping of metals, or enzyme-mediated changes in redox state. Examples include precipitation of uranyl phosphates due the activity of enzymes such as phosphatases, formation of chelating agents in response to metal stress, and precipitation of uraninite through enzymatic uranium reduction. 

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