Cooling rupture

In order to produce martensite and bainite the tube must have been overheated to at least the A3 temperature of 870°C (Fig. 13.4). When the rupture occurred the rapid outrush of boiler water and steam cooled the steel rapidly down to 264°C. The cooling rate was greatest at the rupture edge, where the section was thinnest high enough to quench the steel to martensite. In the main bulk of the tube the cooling rate was less, which is why bainite formed instead. 

Investigate the effect of the pressure surge on adjacent equipment per the 1997 edition of API RP-521. The design pressure of adjacent equipment and piping may be exceeded during a tube rupture. This is of special concern in cooling water networks. Dynamic simulation can assess the impact of a tube rupture on adjacent equipment and identify corrective measures. 

A runaway reaction occurs when an exothermic system becomes uncontrollable. The reaction leads to a rapid increase in the temperature and pressure, which if not relieved can rupture the containing vessel. A runaway reaction occurs because the rate of reaction, and therefore the rate of heat generation, increases exponentially with temperature. In contrast, the rate of cooling increases only linearly with temperature. Once the rate of heat generation exceeds available cooling, the rate of temperature increase becomes progressively faster. Runaway reactions nearly always result in two-phase flow reliefs. In reactor venting, reactions essentially fall into three classifications ... 

Two types of initiators are internal and external. Internal initiators result from failures within a plant or the plant s support utilities. Thus, vessel rupture, human error, cooling failure, and loss of offsite power are internal events. All others are external events earthquakes, tornados, fires (external or internal), and floods (external or internal). Event trees can be used to analyze either type of initiator. 

External events are accident initiators that do not fit well into the central PSA structure used for "internal events." Some "external events" such as fire due to ignition of electrical wires, or flood from a ruptured service water pipe occur inside the plant. Others, such as earthquakes and tornados, occur outside of the plant. Either may cause failures in a plant like internal events. External initiators may cause multiple failures of independent equipment thereby preventing action of presumably redundant protection systems. For example, severe offsite flooding may fli 1 the pump room and disable cooling systems. An earthquake may impede evacuation of the nearby populace. These multiple effects must be considered in the analysis of the effects of external events. 

Many accidents, particularly on batch plants, have been due to runaway reactions, that is, reactions that get out of control. The reaction becomes so rapid that the cooling system cannot prevent a rapid rise in temperature, and/or the relief valve or rupture disc cannot prevent a rapid rise in pressure, and the reactor ruptures. Examples are described in the chapter on human error (Sections 3.2.1 e and 3.2.8), although the incidents were really due to poor design, which left traps into which someone ultimately fell. 

At 8 30 A M., water pumped from a canal became available. It was used to cool other exposed spheres, but the sphere from which the initial spill of propane occurred was not protected. At 8 40 the sphere ruptured into five large fragments, producing a large fireball, killing or injuring nearly 100 people in the vicinity. 

A tube has failed in one of the four condensers about once every three years. If a condenser tube fails, the affected condenser can be removed from service by closing four isolation valves (propane vapor inlet valve), liquid propane outlet valve, cooling water supply valve, and cooling water return valve). However, if a tube fails, it is essential that the operator close the two propane isolation valves before closing the two water isolation valves. Closing the two water valves first would allow pressure to build on the tube side of the condenser and rupture the tube head. 

Interaction of a mixture in a pressure vessel at —78°C caused it to rupture when moved from the cooling bath. 

Addition of sulfuric acid to the cyano-alcohol caused a vigorous reaction which pressure-ruptured the vessel [1]. This seems likely to have been caused by insufficient cooling to prevent dehydration of the alcohol to methaciylonitrile and lack of inhibitors to prevent exothermic polymerisation of the nitrile [2],... 

Significant heat generation during the breakdown also means that cooling must be efficient if the mill is in constant use. Stronger than normal breaker plates commensurate with the overall strength of the mill body will also need to be fitted, otherwise production will be frequently interrupted due to rupture of weaker breaker plate units. 

To overcome the possibility of a vessel rupture from a hydrocarbon fire exposure several methods are available. Depressuring, insulation, water cooling or draining are usually employed in some fashion to prevent of the possibility of a vessel rupture from it s own operating pressures. A generalized method to qualitatively determine the effect of a hydrocarbon fire on the strength of vessels constructed of steel is available. With this method one can estimate the time for a vessel to rupture and therefore the need to provide protective measures. 

Thermoplastic polymers can be heated and cooled reversibly with no change to their chemical structure. Thermosets are processed or cured by a chemical reaction which is irreversible they can be softened by heating but do not return to their uncured state. The polymer type will dictate whether the compound is completely amorphous or partly crystalline at the operating temperature, and its intrinsic resistance to chemicals, mechanical stress and electrical stress. Degradation of the basic polymer, and, in particular, rupture of the main polymer chain or backbone, is the principal cause of reduction of tensile strength. 

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