Cooling failure mechanisms

Many sources contain scattered information concerning cooling water system corrosion and defects, and many literature studies describe corrosion processes and mechanisms from a predominantly theoretical viewpoint. Until now, however, no source discusses cooling water system corrosion with emphasis on identification and elimination of specific problems. Much of the information in this book is unique every significant form of attack is thoroughly detailed. Color photos illustrate each failure mechanism, and case histories further describe industrial problems. 

Now let us consider utility failure as a cause of overpressure. Failure of the utility supphes (e.g., electric power, cooling water, steam, instrument air or instrument power, or fuel) to refinery plant facihties wiU in many instances result in emergency conditions with potential for overpressuring equipment. Although utility supply systems are designed for reliability by the appropriate selection of multiple generation and distribution systems, spare equipment, backup systems, etc., the possibility of failure still remains. Possible failure mechanisms of each utility must, therefore, be examined and evaluated to determine the associated requirements for overpressure protection. The basic rules for these considerations are as follows ... 

Ultimate failure of noncooled specimen NC occurred at 49 min very suddenly through a complex mixed global-local mode, as shown in Figure 6.29. This failure mechanism will be further discussed in detail in Chapter 7. Water-cooled specimens WCl and WC2 did not fail during the plaimed fire endurance time 60 and 120 min, respectively. 

Thermomechanically induced failures are a consequence of the internal stresses which can be established because of the mismatch between the thermal expansion coefficient of the plastic ( 25x 10 per°C), and those of the die and the leadframe ( 12x 10 per°C). These stresses build up when the plastic cools down after moulding, and cyclic stresses are induced by changes in temperature during service. Until recently, the most frequently reported failure mechanism caused by the internal stresses was fracture of either the bond wires or the... 

The hydrocarbon lubricating and sealing oils used in mechanical pumps must not be allowed to backstream or creep to the DP and contaminate the DP oil Power failure, cooling failure, or mistakes in operating a diffusion-pumped system can result in pump oil contaminating the processing chamber. In some applications, cryopumps or turbopumps are used instead of DPs to avoid the possibility of oil contamination. 

All areas of the cooling water system where a specific form of damage is likely to be found are described. The corrosion or failure causes and mechanisms are also described. Especially important factors influencing the corrosion process are listed. Detailed descriptions of each failure mode are given, along with many common, and some not-so-common, case histories. Descriptions of closely related and similarly appearing damage mechanisms allow discrimination between failure modes and avoidance of common mistakes and misconceptions. 

Various clinical manifestations may be present in a patient in shock. For example, in the early stages of shock the extremities may be warm because compensatory mechanisms are initiated and the blood flow to the skin and extremities is maintained. If the condition is untreated, the skin and extremities become cool and clammy because of the failure of the compensatory mechanisms and the progression of shock. Thus, more advanced shock may be referred to as... 

Safety. The MR is much safer than the MASR. (1) The reaction zone contains a much smaller amount of the reaction mixture (hazardous material), which always enhances process safety. (2) In case of pump failure, the reaction automatically stops since the liquid falls down from the reaction zone. (3) There is no need to filter the monolithic catalyst after the reaction has been completed. Filtration of the fine catalysts particles used in slurry reactors is a troublesome and time-consuming operation. Moreover, metallic catalysts used in fine chemicals manufacture are pyrophoric, which makes this operation risky. In a slurry reactor there is a risk of thermal runaways. (4) If the cooling capacity is insufficient (e.g. by a mechanical failure) a temperature increase can lead to an increase in reaction, and thus heat generation rate. 

Figure 1-7 presents the causes of losses for the largest chemical accidents. By far the largest cause of loss in a chemical plant is due to mechanical failure. Failures of this type are usually due to a problem with maintenance. Pumps, valves, and control equipment will fail if not properly maintained. The second largest cause is operator error. For example, valves are not opened or closed in the proper sequence or reactants are not charged to a reactor in the correct order. Process upsets caused by, for example, power or cooling water failures account for 11 % of the losses. 

Typical pressure versus time curves for runaway reactions are illustrated in Figure 8-2. Assume that an exothermic reaction is occurring within a reactor. If cooling is lost because of a loss of cooling water supply, failure of a valve, or other scenario, then the reactor temperature will rise. As the temperature rises, the reaction rate increases, leading to an increase in heat production. This self-accelerating mechanism results in a runaway reaction. 

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