Heaters bending

Heater bending usually takes place on bars fastened to the manifold plate tangentially to the groove curvature, and the heater is pushed into the groove with each bending. The minimum bend radius of a tubular heater depends on its diameter and is 5-16 mm [1]. This technique requires a certain amount of experience. 

The most common type of commercial pyrolysis equipment is the direct fired tubular heater in which the reacting material flows through several tubes connected in series. The tubes receive thermal energy by being immersed in an oil or gas furnace. The pyrolysis products are cooled rapidly after leaving the furnace and enter the separation train. Constraints on materials of construction limit the maximum temperature of the tubes to 1500 °F. Thus the effluent from the tubes should be restricted to temperatures of 1475 °F or less. You may presume that all reactor tubes and return bends are exposed to a thermal flux of 10,000 BTU/... 

A typical firebox temperature is 1500°F. Thus, the heater tubes can reach 1300°F on loss of the process flow, even though the fuel flow has been immediately stopped. Tubes with a low chrome content may bend and distort as a result of such overheating. Even at 1000°F, residual liquid left in the tubes when flow is lost may thermally degrade to a carbonaceous solid or heavy polymer that fouls the interior of the tubes. 

Startup heaters - electrical or direct-fired types - are used to heat synthesis gas for the converter dining startup. Some of the problems encountered with these heaters are hydrogen-induced tracks, overheating and flame impingement, thinning at bends, and furnace explosions. Normally, SS321 is used for startup heater coils and the downstream pipeline88. 

The entire 8-inch (20 cm) piping system was insulated and steam traced except for the heater tubes within the heater. Operations assumed the heat transfer fluid froze in the four heater tube passes. Each pass was a bare 4-inch (10 cm) diameter heater tube with 5 bends and the equivalent of 72 ft. (22 m) of straight pipe. The foreman and the operations team discussed the situation and decided to light and maintain a small fire on the burner to slowly thaw the material in the heater tubes. This method had been successful for a startup several weeks earlier. 

It was easy to spot two failed tubes during an inspection of the heater after the fire. One of the 4-inch (10 cm) diameter tubes was swollen like a bubble with a split that was about 2.5 inches (6.4 cm) wide and 4.5 inches (11.4 cm) long. The other tube failure was smaller. The failures were about 6 ft. (1.9 m) from the bottom bend of the tube. 

The tubes of a heater are connected in series by return bends. When cleaning will not be required, welded return bends may be used. Generally, however, each tube will have a header at one end with a removable plug for cleaning. If much cleaning is required, removable plugs will be provided at both ends of each tube. 

In the downhole U-shaped heater of American design (U.S. Patent No. 3004603,10-17-1961), a U-bend piece made of refractory ceramics is installed below the combustion chamber of the heater. Through its walls, the U-bend transfers the heat of combustion to the bottomhole of the well. The products of combustion are then removed from the well through a parallel string of tubing. As the gas-air mixture is supplied to the downhole heater, it is cooled by circulating water. In a variant of the U-shaped heater, a small diameter pipe connects the combustion chamber with... 

RELAY, THERMAL - A switching relay in which a small heater warms a bimetal element which bends to provide the switching force. 

Nakabeppu et al. [58] describe the use of composite cantilevers made from tin or gold deposited on conventional silicon nitride AFM probes to detect spatial variations in temperature across an indium/tin oxide heater. Differential thermal expansion of the bimetallic elements causes the beam to bend. This movement is monitored using the AFM optical lever deflection detection system. In order to separate thermal deflection of the beam from displacement of the cantilever caused by the sample topography, an intermittent contact mode of operation is employed. Measurements were made under vacuum so as to minimize heat loss. A more practical use of this technology is in the form of miniature chemical and thermal sensors [59]. This approach has been used to perform thermal analysis on picolitre volumes of materisd deposited on the end of a bimetallic cantilever [60]. Arrays of such devices have applications as highly sensitive electronic noses . 

Simple bending is carried out by locally heating along the bend line, from both sides, until the material is pliable, using a strip heater. A strip heater can easily be constructed using a heating element inside a box stmc-ture, with the top made from a heat-resisting material. 

Apart from pneumatic conveying, these pipe-bend reaction problems can be of great concern in oil refineries, especially at the outlet of heaters, in particular distillation-unit charge furnaces, where there is... 

Strip heaters present most of the same construction varieties as the band heaters. Strip heaters are commonly used to apply surface heating to dies and molds. Sometimes they act as a radiant heat source in thermoforming or plastic-bending applications. 

Radiant heaters are nonconductive sources that work exceptionally well in plastic thermoforming and bending and welding applications by replasticizing the polymer before the final production processes. The more conamonly accepted industry styles of radiant heaters are ceramic infrared units. Quartz-faced and black body... 

Tubular heaters (see Figure 5.10) have found a use in HR system designs because of their potential to bend and be adapted to the shape of the manifold, and because of their good durability and linear temperature characteristic. 

If a heater is bent according to the dimensions on the manifold drawing, it will not entirely fit into the groove. Manifold manufacturers use special templates for the bending. When ordering spare heaters for non-standard manifolds, it is usually necessary to send the manifold to the manufacturer, or else spare heaters should be purchased together with the manifold. 

U-bend and double U-bend specimens LP turbines, piping, feedwater heaters, condensers, boilers Detects general corrosion, pitting, and SCC double U-bends simulate crevice and galvanic effects... 

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