Failures furnace tube

Heavy ends can further degrade into carbon deposits on the insides of furnace tubes and lead to tube failure. Sometimes the tube blocks completely and prevents a serious spillage, but at other times spillages have produced costly and spectacular fu-es, as in the incident descried in Section 10.7.2 (though that one was not due to accumulation of heavy ends). To prevent tube failures, keep the concentration of heavy ends below 5% and follow the recommendations on furnace operation in Section 10.7.2 [27]. 

Equipment Failure pumps, tubes in heat exchangers and furnaces, turbine drivers and governor, compressor cylinder valves are examples of equipment which might fail and cause overpressure in the process. If an exchanger tube splits or develops a leak, high pressure fluid will enter the low side, overpressuring either the shell or the channels and associated system as the case may be. 

Extremely thin, glassy silicate scales of less than eggshell thickness may sufficiently insulate the tubes of WT boilers and the furnace tube of FT boilers for tube failure to occur through deformation and rupture. 

The Institution of Chemical Engineers markets Ha/ards Workshop 005, which is entitled Furnace Fires and Explosions. [1] One of the advertising leaflets for this workshop makes the following generalization Furnaces are comparatively simple items for a plant, and because they are unsophisticated they tend to be imperfecdy understood by operators and plant managers alike. Their tolerance to abuse is limited, and once abused their useful life can be drastically shortened. Worse still they may fail suddenly, since furnace tubes distort easily and then fracture. Such failure is often severe, with a consequential fire and/or explosion. ... 

Because hydrogen is used in the reforming reaction, materials must be selected according to API 941, except that C-V Mo should not be used (i.e., the minimum alloy for hydrogen service should be lCr-M Mo). As mentioned previously, this is because of C- Mo failures in catalytic reformers that some refiners have related to the catalytic reformer process regeneration. When selecting furnace tubes, for example, it is important to select the steel with the hydrogen resistance based on the metal temperature,... 

A Furnace Tube Failure Case History Is Revisited... 

A furnace tube failure case history is revisited... 

Elevated tenperature damage to refinery furnace tubes may consist of corrosion-dependent failures and temperature-related defects connected with degradation of the steel microstructure and creep damage. At high temperatures, a steel tube may fail due to deformation and creep fracture even at a stress level well below the yield stress, whereas at low temperatures corrosion and microstmcture degradation processes prevail. These two ranges can be determined by yield strength and rupture stress vs temperature curves [8]. 

Centrifugal pumps are subject to mechanical damage when they lose suction pressure or when the discharge flow is blocked. Furnace tubes may overheat and fail when liquid flow through the tubes is greatly reduced. Low-flow trips protect process equipment against these failures. This trip may be used to shut down a pump or block off fuel to a furnace. To test an orifice-type low-flow trip, proceed as follows ... 

Furnace energy conservation, 223 Furnace feed temperature, 26-27 Furnace fouling, 49 Furnace fuel, 315 Furnace oil, 3, 8, 11—12, 14 Furnace thumping (heat transfer equipment), 432—433 Furnace tubes, 31,298-299 failure, 298-299... 

Water-Side Cleanliness. One of the best preventive steps that can be taken to assure safe, dependable operation is the maintenance of boiler-water conditions that will ensure against any internal tube deposits that could cause overheating and failure of furnace tubes. 

However, carburization is more common in the petrochemical processing industry. A notable problem area has been the radiant and shield sections of ethylene cracking furnaces, due to high tube temperatures up to 1150°C. Apart from temperature, an increase in carbon potential of the gas mix is responsible for a higher severity of damage. High carbon potentials are associated with the ethane, propane, naphtha, and other hydrocarbons as reactants that are cracked. Carburization has been identified as the most frequent failure mechanism of ethylene furnace tubes. 

Unfortunately, at about 1250 to 1300°F the eutectic of 99 percent vanadium plus 1 percent sodium melts into a viscous, sticky liquid. At any higher temperature, the mixture will run off a tube without harm. At a lower temperature, it forms the thin protective solid I described. At 1250 to 1300°F, a thick, uneven, and corrosive mixture (perhaps 1 in. in thickness) slowly eats away at localized areas of a furnace tube. The result is extremely localized tube thinning. I was mystified when I first saw such a tube in Aruba, until the local corrosion engineer explained the failure mechanism to me. 

The failure took place in a large water-tube boiler used for generating steam in a chemical plant. The layout of the boiler is shown in Fig. 13.1. At the bottom of the boiler is a cylindrical pressure vessel - the mud drum - which contains water and sediments. At the top of the boiler is the steam drum, which contains water and steam. The two drums are connected by 200 tubes through which the water circulates. The tubes are heated from the outside by the flue gases from a coal-fired furnace. The water in the "hot" tubes moves upwards from the mud drum to the steam drum, and the water in the "cool" tubes moves downwards from the steam drum to the mud drum. A convection circuit is therefore set up where water circulates around the boiler and picks up heat in the process. The water tubes are 10 m long, have an outside diameter of 100 mm and are 5 mm thick in the wall. They are made from a steel of composition Fe-0.18% C, 0.45% Mn, 0.20% Si. The boiler operates with a working pressure of 50 bar and a water temperature of 264°C. 

With a fan-furnace heating system, once the temperature is reached, the fan is controlled to start automatically. Should fan failure occur, provision should be made to damp down the furnace automatically to avoid overheating s causing tube damage. 

At other times the burning of waste products in furnaces to save fuel and reduce pollution has caused corrosion and tube failure. 

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