Separate protection systems

A tank with a fixed cover of plain carbon steel for storing 60°C warm, softened boiler feed water that had a tar-pitch epoxy resin coating showed pits up to 2.5 mm deep after 10 years of service without cathodic protection. Two separate protection systems were built into the tank because the water level varied as a result of service conditions. A ring anode attached to plastic supports was installed near the bottom of the tank and was connected to a potential-controlled protection rectifier. The side walls were protected by three vertical anodes with fixed adjustable protection current equipment. 

Transferring the plant to a safe state using a separate protection system. 

If two diverse and separate protection systems have been installed in accordance with the principles set out above, then any failure of one syston should always be completely independent from a failure of the other system. Hence the probability of simultaneous failure of both systems can be modeled in probabilistic (or quantitative) risk assessmoits as the multiple of the two wholly independent systans failure probabilities. 

Barrier polymers are used for many packagiag and protective applications. As barriers they separate a system, such as an article of food or an electronic component, from an environment. That is, they limit the iatroduction of matter from the environment iato the system or limit the loss of matter from the system or both. In many cases the environment is simply room air, but the environment can be very different, such as ia the case of protecting a submerged system from water. 

Since the standard insulation level (BIL) of a machine, equipment or a system is already defined, according to Tables 11,6. 14.1, 32.1(A), 13.2 and 13.3. the mtichines are aecordingly designed for this btisic insulation (BIL) only. When the prospective surges are expected to be more severe than this, separate protection becomes imperative. This is particularly important for a rotating machine w hich, besides being a dry equipment, also has only a limited space within the stator slots and hence has the smallest BIL of all, as is evident from Table I 1.6. compared to Tables 14.1, 32.1(A) and 13.2. For its comprehensive protection it can be considered in two parts,... 

In the cathodic protection of storage tanks, potentials should be measured in at least three places, i.e., at each end and at the top of the cover [16]. Widely different polarized areas arise due to the small distance which is normally the case between the impressed current anodes and the tank. Since such tanks are often buried under asphalt, it is recommended that permanent reference electrodes or fixed measuring points (plastic tubes under valve boxes) be installed. These should be located in areas not easily accessible to the cathodic protection current, for example between two tanks or between the tank wall and foundations. Since storage tanks usually have several anodes located near the tank, equalizing currents can flow between the differently loaded anodes on switching off the protection system and thus falsify the potential measurement. In such cases the anodes should be separated. 

If the individual materials are separated by insulating couplings but connected to a protection system, the connections must be made through diodes to avoid bimetallic corrosion when the protection system is shut down (see Fig. 11-6). Furthermore, the different protection currents should be adjusted via variable resistors. 

Figure 11 -7 shows the basic circuit diagram for a tank with two domes. The protection current flows via the two interconnected openers of the cover grounding switch to the cathode connection. If one of the covers is opened, the protection current circuit is broken and the tank grounded via the closing contact. The unconnected cable connection of the tank is without current and can be used for measuring potential. By this method, only one tank at a time is separated from the protection system while the other parts of the installations are still supplied with protection current. 

Figure 20-9 shows the negative effect of uninsulated heating elements on corrosion protection. In a 250-liter tank, an electric tube heating element with a 0.05-m surface area was screwed into the upper third without electrical separation, and in the lower third a tinned copper tube heat exchanger with a 0.61 -m surface area was built in. The Cu heat exchanger was short-circuited for measurements, as required. For cathodic protection, a potential-controlled protection system with impressed current anodes was installed between the two heating elements. The measurements were carried out with two different samples of water with different conductivities. 

Manually Controlled System A manually controlled system comprises one or more transformer-rectifiers each with its associated control panels which supply the d.c. to the various anodes installed in the water box spaces. Each transformer-rectifier is provided with its own control panel where each anode is provided with a fuse, shunt and variable resistor. These enable the current to each anode to be adjusted as required. Reference cells should be provided in order to monitor the cathodic protection system. In the case of a major power station, one transformer-rectifier and associated control panel should be provided for separate protection of screens, circulating water pumps and for each main condenser and associated equipment. 

A passive fire protection system requires no action to occur for it to function per its design intent. Examples of passive fire protection methods are fireproofing, spill containment, and physical separation of units and buildings. 

Fire protection systems should be maintained until materials that pose a hazard are removed. A fire water system should be the last item removed or deactivated. When necessary, decommissioning plans must be reviewed with the AHJ. Fires have occurred during removal of equipment due to cutting operations, material still in the equipment, and other hazards. A separate fire hazard analysis should be conducted to determine fire hazards that may be present during a decommissioning of a unit or plant. 

Fire barriers should be considered when the spacing recommended can not be met and hazards are not easily mitigated with active fire protection systems. Barriers, such as walls, partitions, and floors, provide physical separation of spaces and materials. The effectiveness of a fire barrier is dependant on its fire resistance, materials of construction, and the number of penetrations. Inattention to the integrity of penetrations is one of the primary reasons fire barriers fail to provide proper protection. Factors to consider in the design and placement of fire barriers include ... 

Approved lightning protection systems are the integrally mounted system, the separately mounted shielding system (mast type), and the separately mounted shielding system (overhead ground wire). Details of all of these systems are described in the Ref... 

Over the last several decades, separate classification systems have been developed for radioactive and hazardous chemical wastes based on a variety of considerations, the most prevalent being the source of the waste. These classification systems have served their intended purpose of facilitating development of health-protective strategies for waste management and disposal reasonably well. However, they have exhibited a number of shortcomings and undesirable ramifications, which indicate that a new approach to classification of hazardous wastes would be beneficial. 

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