NDTnet - May 1996, Vol.1 No.05

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From needle pipes to pipelines
Tubes and pipes in technical and everyday use

by Wire/Tube Press Office Bernhard Kunzelmann

In the beginning was the hollowed-out tree trunk, one of the first tubes to be crafted by human hand. With a vast array of models in the plant world to inspire him, Homo sapiens had a much easier job inventing the tube than the wheel for which, by contrast, nature had no example to offer. Bamboo and reed are just two examples of plants with hollow stalks. Nature already knew the value of the tubular form, which combines high stability with the capacity to Transport essential substances for growth, such as water and nutrients, out of the earth.

In technical terms, a tube or pipe is a cylindrical, hard hollow body which usually has a round cross-section but can also be oval, square, rectangular or more complex in profile. It is used on the one hand to convey liquid, gas and solid matter and, on the other, as a construction element. Whatever its purpose, the term covers all sizes and diameters, from the smallest needle pipes right up to wind tunnels. No other profile shape with the same material cross-section has such a high flexural strength, which is what makes the tube so important as a load-bearing element in building.

Tubes for transporting purposes

In the past, people always tried to settle close to water. As the size of the settlements grew, it became increasingly difficult to get the water from the source - the spring, pond, river or lake - to the different dwellings. At first, people used open conduits - initially simple trenches, later stone canals. When the springs and sources were exhausted, aqueducts were used to carry water from the mountains into the towns. Some 300 years A.D., the Romans transported water from the Campagna into their capital and some of their impressive waterways can still be marvelled at in modern-day Europe.

Later, the open canals were covered over and used as closed conduits - and thus the pipeline was born. People were also quick to realize the benefits of closed pipes against open canals for removing waste water. Early pipe materials included wood and stoneware (fired clay), but also easy-to-work metals such as bronze, copper and lead. The first closed pipelines were made around 4,000 years ago of fired clay. The oldest metal pipelines date back to 200 years B.C., first made of bronze and later lead. Lead pipes were cast and chiefly used to Transport water. Copper pipes meanwhile were made from chased copper plate which was rolled and subsequently soldered together.

The advent of an economical method of producing large quantities of cast iron in the 14th century laid the foundation for the manufacture of iron pipes. Gunsmiths and cannon-makers were amongst the first to produce iron pipes. Cast iron pipes were used as early as the 15th century to carry water - some dating back to the 16th century are still in use today. Cast iron pipes also accompanied the development of a public gas supply network, for which compression-proof pipes were a matter of safety and therefore absolutely essential.

As more economical steelmaking methods were developed, an opportunity opened up for this material to be used for pipes. The first were forge-welded out of hoop steel, a method already known to gunsmiths in the Middle Ages. Around 1880, the invention of crossrolling by the Mannesmann brothers also made it possible to produce seamless pipes and tubes. With their thicker walls, seamless pipes offered greater stability at a relatively low weight. Oil-prospectors used such pipes to reach deeper reservoirs and by doing so were able to satisfy the growing demand for mineral oil which accompanied the early days of motorisation. The fact that mineral oil could be transported economically over long distances through a pipeline pushed up the demand for steel pipes even further. Soon, pipelines came to be the biggest market in this area, with demand reaching several million tonnes of welded and seamless pipes every year.

The crucial importance of how a pipe is made for the economic efficiency and environment-friendliness of industrial plant can be illustrated with the contemporary example of seamless boiler pipes with inner ribs. For years the power industry has been aiming to reduce fuel consumption and thereby cut CO2 emissions by stepping up efficiency. This can be done by working with higher operating pressures and temperatures. Consequently, plans have been made to set up new power plant in the first decades of the next century, which will run with pressure levels of up to 350 bar (today's maximum is 300 bar), at operating temperatures of around 700 "C (as opposed to 600 'C) and with efficiency increased from fts current 40% to 50%. Operating parameters of this kind can only be used for suitabie products and materials, of which seamless boiler pipes with inner ribs are one example. On account of their internal geometry, these pipes substantially improve the heat transfer between heating and the vapour phase on the inside of the pipe.

Pipes made of nonferrous metals and plastics Thanks to its good corrosion resistance, copper can be used to make pipes for the chemical industry, refrigeration technology and shipbuilding. Alongside their application for installation purposes, the usually seamless copper pipes are also used in capacitors and heat exchangers. For corrosive materials, low temperatures or stringent demands on the purity of the material carried by the pipe, Aluminium and Aluminium alloys are used in pipe construction. Meanwhile, thanks to its high resistance to many aggressive materials, titanium is well- suited to use in chemical engineering.

Plastics belong to the group of newer pipe materials. With the development of methods for producing plastics on an industrial scale in the 1930s, it also became possible to manufacture plastic pipes economically. By the middle of the 30s, plastics were already being used in Germany to make pressure pipelines. Among the chief advantages of plastics are their high corrosion resistance and a substantial chemical resistance to aggressive media. Moreover, the smooth surfaces mean that plastic pipes are not prone to incrustation, which can have a very detrimental effect on their conveying capacity. Pipes supplying drinking water are mostly made of polyethylene (PE) or polyvinyl chloride (PVC). Like ABS (acrylonftrile-butadiene-styrene copolymer) plastics, these two materials are also used for gas pipelines. Thermoplastic materials - alongside PE and PVC these include PP (polypropylene) and PVDF (polyvinylidenefluoride) - can also be used for industrial pipelines. Beyond these, PB (polybutene) and PE-X (cross- linked polyethylene) are also widespread in pipe-making. Plastic pipes find application in areas such as heating technology, shipbuilding, underwater pipelines (the crossing below a river floor from one bank to the other), irrigating and drainage plant, and well-building.

The right choice of material has a crucial bearing on the economic efficiency and safety of a pipe system. Materials therefore have to be selected according to the demands of each specific application. In steel boiler construction, for example, pipes must be made of steel with high temperature stability plus heat and scaling resistance, while special corrosion resistance is all-important in the chemical and foodstuffs industries. Meanwhile, the mineral-oil processing industry requires heat- proof or press-water-resistant steels for its pipes, gas liquefaction and separation, on the other hand, need materials which have special strength at low temperatures. This broad and highly diversified range of requirements has put a fantastic array of materials to use in pipe- making. Alongside the iron and steel, nonferrous metals and plastics mentioned above, these also take in concrete, clay, porcelain, glass and ceramics.

In addition to liquids and gases, solid matter, broken down, as dust or mixed with water in slurry form, is also pumped through pipelines. Gravel, sand or even iron ore can be conveyed in this manner. Pneumatic transportation of grain, dust and chips through pipes is also a widespread practice. Pneumatic tube conveyors, which similarly work with air, are another important mode of transporting solid matter.

Pipes may be several meters in diameter and pipelines many kilometers in length. At the other end of the scale are conduits with tiny, barely perceptible dimensions. One example of their use is as cannulas in medicine - a collective term referring to instruments with a variety of applications, including infusions, injections and transfusions. Their outer diameter ranges from over 5 millimeters to as little as 0.20 millimeters. Cannulas are made of high-quality grades of stainless steel, brass, silver or nickel silver (an alloy of copper, nickel and zinc, sometimes admixed with traces of lead, iron or tin), but also plastics such as polyethylene, polypropylene or Teflon. Often, different materials are combined with one another to produce the individual components. These tiny tubes must have extremely pronounced elastic properties. They may bend but under no circumstances snap. Their surfaces are often nickel[-plated and always highly polished, sometimes even on the inside. The best-known cannulas are hypodermic needles which, in their most common form as sterile disposable syringes, guarantee aseptic use without costly preparation for reutilisation.

Tubes for construction

No matter where we look in our cities today, we can be sure to see tubular steel constructions. They have become an indispensable element of modern building technology. Once again, we took the idea from nature: in tube-shaped straws, bamboo shoots, quills and bones, Mother Nature demonstrated the successful marriage of beauty and function. Yet these excellent static properties remained unexploited until the advent of welding technology made it possible to connect virtually all dimensions of pipes perfectly and with the necessary interaction of forces for use as construction elements.

As an extremely lightweight building element, steel tube combines high strength with low weight. Steel tubes are used as deck supports in shipbuilding, supports in steel superstructures and binders in building construction. They are used as tubular and lattice masts for overhead and overland transmission lines, for trains and trams, and for lighting. Bridges, railings, observation towers, diving platforms, television towers and roof constructions in halls or sports stadiums are all further examples. Steel tube is also a popular" building element for constructions in temporary use, such as halls, sheds, bridges, spectator stands, podiums and other structures for public events, supporting structures and scaffolding, from the small-scale for house renovation right up to building scaffolds.

In plant engineering, steel tube is used to make ladders, shelves, work tables and subframes for machinery and plant. Steel tube also found its way as a construction element into precision components for machinery and equipment. Shafts and rolls or cylinders in hydraulics and pneumatics are just two examples. Beyond these applications, a great volume of steel tube is used in the cycle industry, camping equipment manufacture, the furniture industry, vehicle and car making and the domestic appliances industry.

Be it on water, over land or in the air, the various modes of Transport would be lost without tubes and pipes. Pipes and tubular construction elements are to be found in ships, planes, trains and motor vehicles. A great variety of pipes and tubular profiles are used in car making, both in connection with the motor and with the chassis and bodywork sections. Most recent developments put them to a far more varied range of uses than before, from air suction pipes and exhaust systems through chassis components right up to side-impact tubes in doors and other safety features. One German car makers new lightweight concept takes as its basic subassembly a three-dimensional frame made up of complex Aluminium extruded sections joined together with the aid of pressure-diecast intersections.

Pipes in everyday use

We come into contact with pipes and tubes on a daily basis. It starts in the morning when we go to clean our teeth and squeeze the toothpaste from this tube, which is nothing other than a tube-shaped flexible container. We write notes with a pen, comprising one or more tubes with a smaller tube - the cartridge or refill - inside it. This is the modern equivalent of the quill, a pointed and split tube used in ancient times as a writing instrument and still used today for Arabic script.

We are surrounded everywhere we go and on a virtually constant basis by tubes and pipes, whether at home, on the move or at work. They take the form of lamp stands and furniture elements in chairs or shelves, curtain rails, telescopic aerials on portable and car radios, and rods on umbrellas or sunshades. And when we water the plants or hang out the washing, tubes are our constant companion - on the watering can or the clothes-horse. Pipes Transport electricity, water and gas directly into our homes. Tubes protect visitors to the Duesseldorf Trade Fair Center from the rigours of the Rhineland weather. Pipe constructions are responsible for a pleasant indoor temperature and prevent the hall roofs from falling on our heads. Civil engineers and architects choose special section tube constructions for windows and doors in preference to other solutions. Tubes even have a role to play in our leisure time, providing us with bicycles, training apparatus and sports equipment.

Musical pipes

Musical instrument-making would be unthinkable without tubes and pipes. The tuba illustrates the connection particularly well: the name of this brass instrument is nothing other than the Latin word for tube. Other brass and pipe instruments also take the tube form. The reed used in a variety of wind instruments such as the clarinet, saxophone, bassoon or oboe is a flexible piece of cane which is fixed into the mouthpiece of the instrument or acts as a mouthpiece itself. Organ pipes also rely on the tube shape to create their sound. They are made of lead and tin, zinc or copper and are still crafted today according to a centuries-old Tradition.

CD stands in the shape of organ pipes make for an original link between two musical words. These CD stands are just under two meters in length, accommodate up to 50 CDs and, if required, can be supplied with interior lighting. Normally out of sight but critically important for good sound quality are the bass-reflex pipes found in loudspeakers. With the proper dimensions in length and diameter, these pipes help to reproduce low-pitched tones without any distortion as a result of unwanted flow noise.

Through tubes and pipes flows the lifeblood of progress and without them our lives would not be nearly as comfortable. They make everyday life easier, safer, more attractive, more varied and more interesting. More to the point, though, they have become indispensable for our existence, shaping the development of our lives to lasting effect in the past and undoubtedly continuing to do so in the future.


©copyright Rolf Diederichs 1.May 1996, info@ndt.net
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