Surfaces pipes

For pipelines in service in chemical plants, it is not usually convenient to place a radiation source inside the pipe and position it to irradiate each welded joint. The radioisotope source container maybe placed on the outer surface of the pipe. The radiation beams then pass through two pipe wall thicknesses to expose films placed diametrically opposite the radiation source, also on the outside of the pipe wall. Other methods, such as magnetic particle inspection of welds in steel pipe, or ultrasonic inspection of welds in pipes of all materials, supplement x-rays in many critical appHcations. The ultrasonic tests can often detect the thin, laminar discontinuities parallel to the pipe surface or the incomplete fusion discontinuities along the weld... 

The cobalt deposition rate on new, replacement, or decontaminated recirculation piping surface has been reduced by pretreating the piping using an atmosphere of oxygenated wet steam to form an oxide film (25). Studies have been conducted for both PWRs and BWRs to reduce the cobalt content of materials used in the nuclear parts of the plants, particularly in hardened and wear surfaces where cobalt-base alloys ( 50% Co) are used (26). Some low cobalt materials have been developed however, the use of the materials is limited to replacement parts or new plants. 

Table 5-2 shows values of (h + h ) from single horizontal oxidized pipe surfaces. 

External coils spaced away from the tank wall exhibit a coefficient of around 5.7 W/(m -°C) [1 Btu/(h-ft of coil surface-°F)j. Direct contact with the tank wall produces higher coefficients, but these are difficult to predict since they are strongly dependent upon the degree of contact. The use of beat-transfer cements does improve performance. These puttylike materials of high thermal conductivity are troweled or camked into the space between the coil and the tank or pipe surface. 

Cascade coolers are a series of standard pipes, usually manifolded in parallel, and connected in series by vertically or horizontally oriented U-bends. Process fluid flows inside the pipe entering at the bottom and water trickles from the top downward over the external pipe surface. The water is collected from a trough under the pipe sections, cooled, and recirculated over the pipe sections. The pipe material can be any of the metallic and also glass, impeiMous graphite, and ceramics. The tubeside coefficient and pressure drop is as in any circular duct. The water coefficient (with Re number less than 2100) is calculated from the following equation by W.H. McAdams, TB. Drew, and G.S. Bays Jr., from the ASME trans. 62, 627-631 (1940). 

Figure 3.15 Knife dislodging a dry tubercle from a steel pipe surface.

Pits are more numerous and deeper on the apparent bottom of the pipe. Surfaces between pits are covered with a tenacious, black oxide layer. 

Figure 6.18 Pinhead-sized, shell-like organisms covering a carbon steel pipe surface.

The first term in Eq. (3-27) represents the voltage drop between the reference electrode over the pipeline and the pipe surface. The second term represents the potential difference AU measured at the soil surface (ground level) perpendicular (directly above) to the pipeline. Average values of the values measured to the left and right of the pipeline are to be used (see Fig. 3-24) [2]. In this way stray IR components can be eliminated. The third term comprises the current densities where, in the switched-off state of the protection installation, there is a cell current J. In the normal case J = 0 and also correspondingly AU f = 0 as well as = t/ ff On... 

The impressed current enters the pipe surface at a defect of radius r. The defect can be considered as a point source at a sufficiently large distance compared to the diameter of the pipe. The potential on the surface of the soil is from Table 24-1, line 5 ... 

Fig. 5-12 Effect of external polarization (t/g) on potentials in the crevice between pipe surface and nonadherent PE coating, carbonate-bicarbonate solution at70 C.

The annular space between the outer pipe and the surrounding rock is filled with cement over the whole depth up to the ground in new wells. The purpose of this is to seal the deposits at the top and to keep the fresh water and salt water zones separate. In addition, it serves as a protection against pressure from the rock and as corrosion protection which, however, is only effective so long as there is no current exit caused by extended corrosion of cells or due to foreign anodic influences. The cement Ailing of the borehole casing is usually not uniformly spread over the pipe surface. It has to be remembered that there can be sections which are either not covered or are only thinly covered with cement. 

Here I /G. is the heat exchanger contact resistance. The reason for rhe contact resistance is that there exists a resistance to heat flow between the outer surface of the pipe and the collar of the plate tins. Normally, the fins are attached to the pipes by mechanical expansion of the tubes out into rhe plate-fin collars. Because of this manufacturing method, the contact will not be ideal. Small gaps between the pipe surface and rhe collar of the tins will occur. 

The friction factor depends on the Reynolds number and duct wall relative roughness e/D, where e is the average height ol the roughness in rhe duct wall. The friction factor is shown in Fig. 9.46. For a Urge Reynolds number, the friction factor / is considered constant for rough pipe surfaces. The friction pressure loss is Ap c. ... 

The other detonability length scale is the detonation cell width, X (also called cell size) which is the transverse dimension of diamond shaped cells generated by the transverse wave stmctnre at a detonation front. It has a fish scale pattern (see Figure 4-4). Detonation cell widths are nsnally measured by the traces (soot) deposited on smoke foils inserted in test vessels or piping surfaces. The more reactive the gas-air mixture, the smaller is the cell size. The same is tme for chemical indnction length as a qualitative measure of detonability. The cell width, X, is a parameter that is of practical importance. The transition from dehagration to detonation, propagation, and transmission of a detonation, can to some extent be eval-... 

The authors point out that the emissivity, e, for many pipe surfaces ranges from 0.87-0.92 at approximately 70°F for highly polished aluminum, e = 0.23-0.28. 

Branch lines transfer oil from a ring main circuit to the oil-burning equipment. Where a residual oil fuel is to be used, there will be some cooling of the oil immediately adjacent to the pipe surfaces and this will show as a small increase in viscosity. To keep this variation to a minimum and so prevent any difficulties in atomization at the oil burner, care should be taken over the length and diameter of branch lines. Provision should always be made to isolate and drain branch lines. 

All compressor types have moving parts, high noise levels, high pressures, and high-temperature cylinder and discharge-piping surfaces. 

Recently, sheets of high density polyethylene extruded on to the pipe surface over an adhesive have become available and the use of polyethylene or epoxy powders sintered on to the steel surface is becoming more frequent. 

The British Gas version uses magnetic saturation, and can identify corrosion on both internal and external pipe surfaces. The specification for seamless pipe is ... 

Flood Coat application of coal-tar or bituminous coatings to pipelines by flooding the heated coating materials over the pipe surface wrappings and slings are used to pull the coat underneath the pipe. 

Weekman and Myers (W2) examined the fluid-flow characteristics of cocurrent downward flow of gas and liquid. The pulsing effect first noted by Larkins et al. was also observed in this work. Pressure-drop data could be correlated satisfactorily by a relation similar to those used for two-phase flow in pipes. Surface-active agents were observed to have a pronounced influence upon flow regime transition and pressure drop. 

Region l (Re < 2000) corresponds to streamline motion and a single curve represents all the data, irrespective of the roughness of the pipe surface. The equation of the curve is R/pu2 = 8/Re. 

Now the friction factor R/pu2 is a function of the Reynolds number Re and the relative roughness e/d of the pipe surface which will normally be constant along a given pipe. The Reynolds number is given by ... 

Oil of viscosity 10 mN s/m2 and density 950 kg/m3 is pumped 8 km from an oil refinery to a distribution depot through a 75 inm diameter pipeline and is then despatched to customers at a rale of 500 tonne/day. Allowance must be made for periods of maintenance which may interrupt the supply from the refinery for up to 72 hours. If the maximum permissible pressure drop over the pipeline is 3450 kN/m2, what is the shortest time in which the storage tanks can be completely recharged after a 72 hour shutdown Take the roughness of the pipe surface as 0.05 mm. 

Oil with a viscosity of 10 mN s/m2 and density 900 kg/nr is flowing through a 500 mm diameter pipe 10 km long. The pressure difference between the two ends of the pipe is lO N/m2. What will the pressure drop he at the same flowrate if it is necessary to replace the pipe hy one only 300 mm diameter Assume the pipe surface to be smooth. 

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