Pipe pigs

Cleaning waterlines and fuel pipelines with pipe pigs has been an acceptable practice for many years. However, cleaning pipelines that conveyed explosives with a pipe pig is innovative, and proved to be very effective and economical. 

Many tracer studies are intended to give only qualitative information such as information about the material of which an object is made or the location or route which the material or object is following. An example of this kind of application is the so-called pipe-pig used to clean long pipelines. A radiation source can be installed in the pig in order to localize it in case of blockage. In the early days of the industrial applications of radioisotopes the source in a pipe-pig was typically a lOGBq cobalt-60 source. Nowadays more sensitive radiation detectors are used and short-lived radiotracers like manganese-56 or sodium-24 with activities of 1 GBq are used. These are installed in the pig each time just before the use. 

Lead pipe pig-tails and goose-necks were also used to join other pipe materials, but the lengths involved should be limited to a few metres. 

Pipelines are cleaned and inspected using pigs . Pigs usually have a steel body fitted with rubber cups and brushes or scrapers to remove wax and rust deposits on the pipe wall, as the pig is pumped along the pipe. Sometimes spherical pigs are used for product separation or controlling liquid hold up. In field lines handling untreated crude may have to be insulated to prevent wax formation. 

Methods for (a) to (c) are electromagnetic or use eddy currents. The method for (d) is a mechanical system similar to the caliper pig, in which the probe runs over the inner wall of the pipe over pits, shallow pits and penetration holes. 

Themtal. Thermal relief is needed in a vessel or piping run that is liquid-packed and can be isolated, for example pig launchers and meter provers. Liquid is subject to thermal expansion if it is heated. It is also incompressible. The thermal expansion due to heating by the sun from a nighttime temperature of 80°F to a sun-heated temperature of 120 F can be enough to rupture piping or a vessel. The required capacity of thermal relief valves is very small. 

Gusseisen, n. cast iron pig iron, -rohr, n., -rohre, f. cast-iron pipe, guss-eisem, a. cast-iron, -fahig, a. castable. 

Even carefully built pipelines have been found to contain up to 10 tons of waste materials, mostly iron rust, sand, mud, and welding rods. Even shoes, gloves, and bottles have been removed from pipes. Cleaning can generally be achieved by pumping suitable solvents in pigging operations. 

J. Bissell, D. Acker, and L. R. Quaife. Pipeline leak-location technique utilizing a novel test fluid and trained dogs. In Proceedings Volume, number 9. 5th Pipe Line Ind Pipes Pipelines Int Pipeline Pigging Integrity Monit Int Conf (Houston, TX, 2/1-2/4), 1993. 

M. A. Keimard and J. G. McNulty. Conventional pipeline-pigging technology Pt 2 Corrosion-inhibitor deposition using pigs. Pipes Pipelines Int, 37(4) 14-20, July-August 1992. 

R. J. Purinton, Jr. and S. Mitchell. Practical applications for gelled fluid pigging. Pipe Line Ind, 66(3) 55-56, March 1987. 

Introducing mechanical cleaning of vessels (e.g. wall wipers) and pipes (e.g. pipeline pigging) that process viscous materials and require periodic cleaning with water. 

Many varieties of pigs are available, some of which are quite sophisticated. However, very simple pigs are sufficient for most pipe cleaning operations in the explosives industry. 

The pipes to be cleaned may be of almost any length. A means of ingress and egress for the pig must be provided, all valves in the line to be cleaned must be fully open. (Valves in any branch line should be kept closed, to insure the pig follows the path of least resistance — the main line.)... 

Before adopting this method at the ordnance plant, sections of pipelines were chosen for test samples, to determine if the swab and pig method would satisfactorily clean these contaminated pipes. One half the sections were cleaned by this method and the other half was thoroughly flushed with water. They were allowed to dry and then were subjected to initiation by fires. The sections that had been flushed with water ignited and burned vigorously. The sections that had been subjected to cleaning with the swab and pig had no product remaining that would support combustion. 

Example 2.10. Probably the best contemporary example of a variable-mass system would be the equations of motion for a space rocket whose mass decreases as fuel is consumed. However, to stick with chemical engineering systems, let us consider the problem sketched in Fig. 2.8. Petroleum pipelines are sometimes used for transferring several products from one location to another on a batch basis, i.e., one product at a time. To reduce product contamination at the end of a batch transfer, a leather ball or pig that just fits the pipe is inserted in one end of the hne. Inert gas is introduced behind the pig to push it through the hne, thus purging the hne of whatever hquid is in it. 

To write a force balance on the hquid stiU in the pipe as it is pushed out, we must take into account the changing mass of material. Assume the pig is weightless and fiictionless compared with the hquid in the hne. Let z be the axial position of the pig at any time. The hquid is incompressible (density p) and flows in plug flow. It exerts a frictional force proportional to the square of its velocity and to the length of pipe stiU containing hquid. 

To prevent backflow and to prohibit organisms entering the pipe, duckbill valves can be installed on the end of diffuser ports. An example of this can be seen in Pig 4.2. These valves can be selected with varying operating pressures to ensure all valves along a diffuser open at the same time as the pressure of the concentrate drops along the pipe (Mauguin and Corsin 2005). 

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