Failures heat transfer system

Heat transfer systems are normally provided to utilize available process heat, to economize heat for distillation purposes or to preheat fuel supplies before usage. They are generally considered a secondary process support system to the main production process, however they may be so critical to the process that they might be considered a single point failure if not adequately designed. 

Hydrate formation is possible only at temperatures less than 35°C when the pressure is less than 100 bar. Hydrates are a nuisance they are capable of plugging (partially or totally) equipment in transport systems such as pipelines, filters, and valves they can accumulate in heat exchangers and reduce heat transfer as well as increase pressure drop. Finally, if deposited in rotating machinery, they can lead to rotor imbalance generating vibration and causing failure of the machine. 

Water Treatment. Water and steam chemistry must be rigorously controlled to prevent deposition of impurities and corrosion of the steam cycle. Deposition on boiler tubing walls reduces heat transfer and can lead to overheating, creep, and eventual failure. Additionally, corrosion can develop under the deposits and lead to failure. If steam is used for chemical processes or as a heat-transfer medium for food and pharmaceutical preparation there are limitations on the additives that may be used. Steam purity requirements set the allowable impurity concentrations for the rest of most cycles. Once contaminants enter the steam, there is no practical way to remove them. Thus all purification must be carried out in the boiler or preboiler part of the cycle. The principal exception is in the case of nuclear steam generators, which require very pure water. These tend to provide steam that is considerably lower in most impurities than the turbine requires. A variety of water treatments are summarized in Table 5. Although the subtieties of water treatment in steam systems are beyond the scope of this article, uses of various additives maybe summarized as follows ... 

Cooling System Corrosion Corrosion can be defined as the destmction of a metal by chemical or electrochemical reaction with its environment. In cooling systems, corrosion causes two basic problems. The first and most obvious is the failure of equipment with the resultant cost of replacement and plant downtime. The second is decreased plant efficiency to loss of heat transfer, the result of heat exchanger fouling caused by the accumulation of corrosion products. 

Loss of Heat Sink Failure of heat transfer between the primary and secondary cooling systems requiring emergency cooling. 

Fire protection systems achieve exposure protection by absorption of heat through application of extinguishing agents to structures or equipment exposed to a fire. The application of some extinguishing agents removes or reduces the heat transferred to the structures or equipment from the exposing fire, as well as limits the surface temperature of exposed structures and equipment to a level that will minimize damage and prevent failure. 

Some typical values of heat transfer coefficients are given in Table 9.5. The values provided for hr without stirrer and hc without flow, show the influence of failure of the stirrer or of the cooling system on the heat transfer. 

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