Stable pipe

The presence of these acids in crude oils and petroleum cuts causes problems for the refiner because they form stable emulsions with caustic solutions during desalting or in lubricating oil production very corrosive at high temperatures (350-400°C), they attack ordinary carbon steel, which necessitates the use of alloy piping materials. 

The phenomena are quite complex even for pipe flow. Efforts to predict the onset of instabiHty have been made using linear stabiHty theory. The analysis predicts that laminar flow in pipes is stable at all values of the Reynolds number. In practice, the laminar—turbulent transition is found to occur at a Reynolds number of about 2000, although by careful design of the pipe inlet it can be postponed to as high as 40,000. It appears that linear stabiHty analysis is not appHcable in this situation. 

Differential pressures and subatmospherie pressures should be measured by manometers with a fluid that is ehemieally stable when in eontaet with the test gas. Mereury traps should be used where neeessary to prevent the manometer fluid from entering the proeess piping. Errors in these instruments should not exeeed 0.25%. 

Another method of test is to test all sections simultaneously. In this method, the weight flow through each section is maintained in the same proportion. A separate gas cooler is required for each stream and the loop must have sufficient capacity to enable stable conditions to be obtained. In this system, the machine is tested as fully built but requires extensive shop test space to accommodate the multiple gas coolers and large test-loop piping required, if there are several sidestreams. 

The dense-phase regime can be further subdivided into three distinct regions,which are shown in Fig. 14.3. In continuous dense-phase flow the material moves by saltation over a stable creeping bed, in discontinuous dense-phase flow particles move as groups, and in the solid dense-phase the solids are extruded through the pipe as a continuous slag. 

When MEA is used in the presence of COS and CS2, they react to form heat-stable salts. Therefore, MEA systems usually include a reclaimer, The reclaimer is a kettle-type reboiler operating on a small side stream of lean solution. The temperature in the reclaimer is maintained such that the water and MEA boil to the overhead and are piped back to the stripper. The heat-stable salts remain in the reclaimer until the reclaimer is full. Then the reclaimer is shut-in and dumped to a waste disposal. Thus, the impurities are removed but the MEA bonded to the salts is also lost. 

Overdriven detonation is the condition that exists during a DDT before a state of stable detonation is reached. Transition occurs over the length of a few pipe diameters and propagation velocities np to 2000 m/s have been measnred for hydrocarbons in air. This is greater than the speed of sonnd as measnred at the flame front. Overdriven detonations are typically accompanied by side-on pressnre ratios (at the pipe wall) in the range of 50-100. A severe test for detonation flame arresters is to adjust the mn-np distance so that DDT occurs at the arrester, subjecting it to the overdriven detonation impulse. 

Overdriven detonations, not long-pipe stable detonations, provide a greater potential for mechanical damage to detonation flame arresters. 

The detonation flame arrester mnst be able to arrest ten deflagrations with and withont a pipe restriction downstream of the flame arrester and five nnrestricted stable and overdriven detonations. The UL standard states, after tests determine the maximnm nnsta-ble (overdriven) detonation, the arrester is to be snbjected to fonr additional nnstable detonations with the length of pipe that resnlted in the maximnm nnstable (overdriven) detonation. The arrester is also to be snbjected to five stable detonations. ... 

Standard Test Pipe Test Gas Stable Detona- tion Over- driven Detona- tion Deflagra- tions Test Pressure Endur- ance Burn Test... 

A denotes straight pipe fejr stable deteniatienis B denejtes straight pipe, clejsed end fejr stable deteniatienis restr. denejtes a pipe with a restricted end unrestr. denejtes a pipe with an unrestricted end... 

It is important to recognize that a cenlrijugal pump will operate only along its performance curve [10, II]. External conditions will adjust themselves, or must be adjusted in order to obtain stable operation. Each pump operates within a system, and the conditions can be anticipated if each component part is properly examined. The system consists of the friction losses of the suction and the discharge piping plus the total static head from suction to final discharge point. Figure 3-51 represents a typical system head curve superimposed on the characteristic curve for a 10 by 8-inch pump with a 12-inch diameter impeller. 

No matter how well insulated, buildings will need a continual input of heat to maintain desired temperature levels. The input required will be much smaller in a well-insulated building than in uninsulated ones - but it will still be needed. The same applies to items of plant - pipes, vessels and tanks containing hot (or cold) fluids. If there is no heat input to compensate for the loss through the insulation the temperature of the fluid will fall. A well-insulated vessel will maintain the heat of its contents for a longer period of time but it will never, on its own, keep the temperature stable. 

For stable operation of the valves some appreciable volume between them is necessary. A length equal to 50 diameters of the appropriately sized pipe is often recommended or the same volume of larger pipe. 

Although the Langelier index is probably the most frequently quoted measure of a water s corrosivity, it is at best a not very reliable guide. All that the index can do, and all that its author claimed for it is to provide an indication of a water s thermodynamic tendency to precipitate calcium carbonate. It cannot indicate if sufficient material will be deposited to completely cover all exposed metal surfaces consequently a very soft water can have a strongly positive index but still be corrosive. Similarly the index cannot take into account if the precipitate will be in the appropriate physical form, i.e. a semi-amorphous egg-shell like deposit that spreads uniformly over all the exposed surfaces rather than forming isolated crystals at a limited number of nucleation sites. The egg-shell type of deposit has been shown to be associated with the presence of organic material which affects the growth mechanism of the calcium carbonate crystals . Where a substantial and stable deposit is produced on a metal surface, this is an effective anticorrosion barrier and forms the basis of a chemical treatment to protect water pipes . However, the conditions required for such a process are not likely to arise with any natural waters. 

The effect of pH on the corrosion of zinc has already been mentioned (p. 4.170). In the range of pH values from 5 -5 to 12, zinc is quite stable, and since most natural waters come within this range little difficulty is encountered in respect of pH. The pH does, however, affect the scale-forming properties of hard water (see Section 2.3 for a discussion of the Langelier index). If the pH is below the value at which the water is in equilibrium with calcium carbonate, the calcium carbonate will tend to dissolve rather than form a scale. The same effect is produced in the presence of considerable amounts of carbon dioxide, which also favours the dissolution of calcium carbonate. In addition, it is important to note that small amounts of metallic impurities (particularly copper) in the water can cause quite severe corrosion, and as little as 0-05 p.p.m. of copper in a domestic water system can be a source of considerable trouble with galvanised tanks and pipes. 

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