Tubing metal

Fig. 6. Boiler water contamination of the steam caused superheater deposits, which led to tube metal overheating and failure.

FIG. 27-40 Elffect of departure from nucleate boiling (DNB) on tube-metal temperature. 

General description. Burnthrough as discussed here specifically refers to the melting of tube metal in the vicinity of the weld such that a cavity is formed. If burnthrough is severe, a continuous channel may be produced that can cause leakage. 

Tubeside fouling Shellside fouling Tube metal wall Tubeside film resistance Shellside film resistance... 

Metall-salzUSsung, /. metallic-salt solution, -saure, /. metallic acid (as HMn04). -schlacke,/. metal slag, -schlauch, m. (flexible) metallic tube, metallic hose, -schliff,... 

Often this may be assumed based upon the temperature of the fluids flowing on each side of the tube wall. For a more accurate estimate, and one that requires a trial-and-error solution, neglecting the drop-through tube metal wall (usually small) ... 

Flexible tubes Metallic tubes complying with BS 669, Part 2 or BS 6501 shall be used other than with small portable appliances or with domestic-type appliances, in which case they shall comply with BS 669 Part 1. A manual valve shall be fitted on the inlet side in close proximity to the tube. The pipework shall be adequately supported such that the tube does not support the weight of the attached pipework. Tubes shall be installed so that they are neither twisted nor subjected to torsional strain, have flexing in one plane only, and are not subject to sharp bends near end fittings. 

This type of stress-related corrosion process may result in boiler failure through a sudden and violent rupturing of the boiler tube metal. Austenitic stainless steels also are corroded by SCC mechanisms in the presence of concentrated chlorides (chloride-induced SCC). 

Metals Metals are used as collapsible tubes and in aerosol containers. The most common metals in use are tin, aluminum, and lead. Tin is the most expensive, while lead is the cheapest. Laminates of tin-coated lead provide the appearance and oxidation resistance of straight tin at lower prices [89]. Tin is the most chemically inert of all collapsible tube metals. It offers a good appearance and compatibility with a wide range of products. Aluminum tubes provide the attractiveness of tin at relatively lower cost. Lead has the lowest cost of all tube metals and is widely used for nonfood products such as adhesives. However, with internal linings, lead tubes are used for such products as fluoride toothpaste. If the product is not compatible with bare metal, the interior can be flushed with wax-type formulations or with resin solutions. 

The expl props, as detd by Haid et al (Ref 8), indicate that Ca azide is the most powerful of the alkaline earth azides. Although Curtius found that this salt did not expl by percussion, Wohler Martin (Ref 5) and Haid et al (Ref 8) obtained deton by impact (Refs 7 12). When heated rapidly Ca(Nj)3 expl between 144-156°. Heated in a capillary tube, metallic Ca appears at 120-130° (Ref 11) and in vacuo expl between 160-170° (Ref 14). The kinetics of the thermal decompn has been studied by Andreev (Ref 10), Garner Reeves (Ref 19) and others ionic conductance of the solid by Jacobs Tompkins (Ref 18) in the temp range 290-370°K, and initiation and propogation of expln by Bowden Williams (Ref 16) who measured the rate of deton as 770 m/sec. 

Tt = the receiving metal temperature, °F (this is the radiant tube metal or tube skin temperature). 

A typical process heater tube diameter is 4 to 10 in. Tube thickness is usually between V4 and V2 in. Heater tubes are often constructed out of chrome steel. A high chrome content is 13 percent. The chrome content increases the heat resistance of the tube. A tube with a 11 to 13 percent chrome content can normally withstand a skin temperature of up to 1300 to 1350°F. A low-chrome-content tube of perhaps 3 percent may be limited to 1200°F tube metal temperature. Naturally, the pressure, thickness, and diameter of the tube all affect its maximum skin temperature limitations. 

When the tube metal temperature exceeds a value of 1300 to 1400°F, it becomes plastic. This means that the pressure inside the tube causes... 

The feed-effluent heat exchanger is assumed to be single-pass, countercurrent shell-and-tube design. Three partial differential equations are used for the temperatures of gas on tube side, gas on shell side, and the tube metal Eqs. (6.11), (6.12), and (6.13), respectively. The overall heat transfer coefficients on both tube and shell sides, U, and U are constant and are equal to 0.284 kJ s-1 m-2 K-1. Equal heat transfer area per volume is assumed for the shell and tube sides (A,/V, = As/Vs) and is 157 m2/m3, based... 

The FEHE is modeled by assuming the cold gas has a temperature Tc in the nth lump, into which heat is transferred at a rate Qc from the hotter tube metal at temperature TMn ... 

The hot gas flows countercurrently and has a temperature THn in the nth lump. Heat is transferred from the hot gas into the tube metal at a rate Q, ... 

Compared to a fired reformer, catalyst tube damage is less likely. This is because direct flame impingement cannot occur, and flue gas distribution is not a concern. The maximum tube metal temperature is also limited to the temperature of the shell-side gases. Since die reformer burners have been eliminated, process control is less complicated. And the lack of a flue gas stream reduces emissions of NOx and C02 by as much as 60% to 75%203. 

The shutdown setpoint was found to have been mistakenly raised to the maximum of the instruments setpoint range, or 1600° F (870° C). (The tube metal high temperature... 

The shutdown setpoint was found to have been mistakenly raised to the maximum of the instrument s setpoint range or 1600° F (870° C). (The tube-metal high temperature alarm should have been fixed at 830° F (443° C) and the shutdown temperature should have been 850° F (454° C).) The investigating team concluded the limited burner shutdown instrumentation had not been properly inspected and tested to insure the necessary high degree of reliability. Perhaps the instrumentation was troublesome. If just a high tube metal temperature warning alarm would have sounded, the loss may have been minimized. 

Heat exchangers are treated in a manner similar to columns (i.e., 12Cr clad shells and channels and 5Cr- Mo tubes are usually used above 550° F [288°C]). When selecting materials for exchangers, one must take into account crevices, changes in direction, and actual tube metal temperatures (since the tubes are exposed to fluids of different temperatures). 

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