Resistance control protection

Resistance control protection Increase in resistance of corrosion cell R... 

In addition to secondarv resistance control, other devices such as reactors and thyristors (solid-state controllable rectifiers) are used to control wound-rotor motors. Fixed secondary reactors combined with resistors can provide veiy constant accelerating torque with a minimum number of accelerating steps. The change in slip frequency with speed continually changes the effective reac tance and hence the value of resistance associated with the reactor. The secondaiy reactors, resistors, and contacts can be varied in design to provide the proper accelerating speed-torque curve for the protection of belt conveyors and similar loads. 

Cathodic protection. The potential must be kept below the protection potential. An efficient method for internal protection of pipe joints is the resistance-controlled cathodic protection (RCP) (see Section 10.4).4. 

For pipe systems of stainless steel carrying chlorinated seawater, internal localized corrosion can be very efficiently prevented by the application of Resistance-controlled Cathodic Protection (RCP). A resistance is simply inserted between the sacrificial anode and the pipeline, and this makes a system that is particularly suitable when there is a low diffusion-limiting cathodic current in the critical potential range [10.29]. Typical of the method is that the current output from the anode is kept low, which has the consequence that the voltage drops are low and the protected pipe length from each anode is long. 

Organic coatings include phenol formaldehyde, epoxy, polyacryl and polyacryl acid resins, polyamide, polyolefin, bitumen and rubber. The required properties of lining materials in combination with cathodic protection are given in Section 5.2.1. In addition, adequate resistance to water vapor diffusion is required (see Section 5.2.2). These properties are discussed in the basic standard for internal cathodic protection [2], which also reports how these properties can be assured by testing with the aid of Ref. 3. It is convenient to limit the protection potential region to [7 5 = -0.8 V in the presence of resin coatings, which makes potential-controlled protection current equipment necessary. 

The electrical conductivity of the electrolyte, the temperature, and the surface condition determines the galvanic action of the sacrificial metal coating. An increase in the cathodic overpotential is responsible for the corrosion resistance of the coating layer. Figure 16.8 shows the principle of cathodic control protection by a sacrificial metal coating. 

Arc-resistant control equipment, including low voltage (LV) and medium voltage (MV) control centers, are designed, tested and built to contain and redirect the energy away from personnel. The level of protection for those working around arc-resistant equipment is defined by an Accessibility Type. 

Several differential mass balance models have been proposed to characterize mass transfer kinetics. Among them, the model proposed by Sovova (1994), based on extraction from broken and intact cells (BICs), has been widely used. In this model, the solutes are stored in particle cells and protected by the cell wall. During the pretreatment step, to reduce the particle size and increase the surface area between the solute and fluid, some of the cells are broken and solutes become accessible to the fluid. These easily accessible solutes are denoted as x. The remaining solutes retained in unbroken cells are referred to as intact cells and defined as x. Thus, internal and external resistance control the extraction. Sovova (2005) also proposed a more complete model with additional parameters to consider equilibrium relationships. However, this modified model has not been widely used, due to its complexity, and most published work continues to use the older BIC model with mass transfer coefficients in the fluid (k ) and solid (k) phases, and x as the main parameter. The following assumptions are usually considered ... 

Zhou D, Gruen DM, Qin LC, McCauley TG, Krauss AR (1998) Control of diamond film microstructure by Ar additions to CH4/H2 microwave plasmas. 1 Appl Phys 84 1981. Sumant AV, Krauss AR, Gruen DM, Auciello O, Erdemir A, Williams M, Artiles AF Adams W (2005) UltrananocrystaUine Diamond Film as a Wear-Resistant and Protective Coating for Mechanical Seal Applications. Tribol Trans 48 24. 

Lead and many of its ahoys exhibit excehent corrosion resistance owing to the rapid formation of a passive, impermeable, insoluble protective film when the lead is exposed to the corrosive solution (see Corrosion and corrosion control). 

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