When assembling transportation networks for various purposes, for example, heating communications or highways designed for the distillation of oil and gas, until recently, mainly ordinary pipes made of steel were used. For the most part, products of this type still cope quite well with their work. However, such pipes still have one rather serious drawback. Whatever the thickness of their walls, they cannot protect the distilled liquid from the cold in the winter.
The result of freezing water or coolant in the mains usually becomes the failure of the latter. At the same time, in steel networks during the cold season, there are, among other things, significant heat losses, which makes their operation much more expensive.
What are PPU pipes
To prevent freezing of liquids transported along the highways, the latter, when assembling the network on the street, is either laid very deep underground, or they are additionally insulated using special materials. Both that and other methods differ in labor input and technological complexity. Therefore, recently, pipes of a special design - pre-insulated - have become increasingly popular.
Products of this type are insulated at the production stage using a modern insulator, characterized by a very low degree of thermal conductivity - polyurethane foam. Such pipes cost more than usual. However, the lines assembled from them can serve in the future without the need for repair for a decade.
PPU pipe construction
Externally, such products are very similar to well-known to many sandwich chimneys. That is, they consist of three main layers:
the steel pipe itself, through which liquid will be pumped in the future;
a layer of polyurethane foam;
outer containment.
In the layer of polyurethane foam in such pipes pass special signal cables. Due to their presence, it is always possible to accurately determine the location of an accident on the highway and quickly carry out repairs.
What specifications may have
Pre-insulated pipes are now available in a wide assortment on the market. Such products may vary in:
The cost of products of this variety directly depends on their diameter and thickness of the insulating layer. According to the last indicator, PPU pipes are selected taking into account the climate of the region in which the network is supposed to be assembled, as well as the depth of the latter. In warm areas, pipelines with a thickness of the insulation layer of 5 cm are usually collected. In the northern regions, pipes with an insulating layer of 10 cm or more are used.
Signal cables in the insulation layer of such products, depending on the diameter, can be laid two or three.
GOST Standards
Pre-insulated pipes are produced in our country with strict observance of the requirements of GOST. The insulation used in the manufacture of such products, in any case, must meet the following requirements:
water absorption by volume - 10%;
compressive elasticity - not less than 0.3 MPa (deformation in all directions - up to 10%);
density - up to 60 kg / m 3 .
When heated to 110 ° C, the length of the insulator used in the assembly of pipes of the PUF pipe should not exceed 3%.
Polyurethane foam for pipe insulation can be manufactured using various technologies. But most often such material is made on the basis of carbon dioxide and freon. In most cases, in the manufacture of PPU pipes, polyurethane foam of such well-known brands as Dau, Izolan, Huntsman, and Elostokam is used.
Design Types
There are currently two main types of pre-insulated pipes on the market:
Products of the first variety are made of ordinary or galvanized steel with polyurethane foam insulation. Outside, such pipes are sheathed with sheets of hard steel or stainless steel.
Flexible products of this type are manufactured using similar technology. However, such pipes are not sheathed in steel, but in corrugated plastic. Of course, such products are not too flexible. After all, polyurethane foam - the material itself is quite rigid and not too elastic. However, it is still possible to bend the pipes of this variety a little when laying.
Of course, in the manufacture of plastic shells of pre-insulated pipes, GOSTs are also observed without fail. Used for their assembly is usually the highest quality light stabilized material.
Sometimes protective shells with an insulating layer can be supplied separately from the pipes themselves. In this case, before installation, when assembling the trunk, the pipes are pre-tested for leaks and then coated with an anti-corrosion compound.
How is an insulation layer applied to a PU foam pipe
Many domestic plants produce such products. Pre-insulated pipes are also supplied to the Russian market, of course, by foreign companies.
Judging by the reviews, then domestic products of this type in quality today at a lower cost are practically inferior to imported ones. For example, such products manufactured by the Novosibirsk Pre-insulated Pipe Plant, the Oryol Pipe Insulation Plant, the Stroiizolyatsiya Plant (Seversk), etc., deserved excellent customer reviews.
In any case, in the manufacture of such products, specialists without fail, among other things, make sure that the adhesion between the polyurethane foam and the steel pipe is as strong as possible. So that the insulation does not slip on steel and holds as reliably as possible, before applying it, the base should be carefully cleaned until a rough surface is formed while rust is removed.
When foaming the polyurethane foam itself, the specified thermal regime must be precisely maintained. The adhesion between the inner shell and the foam filler can also be improved by treating the latter discharge.
To prevent the still-frozen insulator from leaking out, a special metal plug is attached from the end of the pipe. After the material has hardened, this element is removed from the pipe of the preisolated PPU. Such products go on sale with an open end of the polyurethane foam layer.
Scope of use
The most widely used PPU pipes at the moment are, of course, primarily in industry. Such products are used during assembly mainly:
oil pipelines;
gas pipelines;
steam pipelines.
Very often, pre-insulated pipes are also used for heating networks intended for pumping heated liquids. Such communications are usually mounted in hot shops of enterprises of different specializations.
Recently, pre-insulated pipes began to gain immense popularity among public utilities. Organizations of this specialization use these products when laying centralized heating systems and water pipelines in cities and towns. The use of such pipes in this case can significantly improve the quality of public services.
Main advantages
Pre-insulated pipes for heating mains, water pipelines, oil pipelines, etc., or rather, for assembly, are used in our country, therefore, quite often. But what explains the popularity of modern products of this type?
The unconditional advantages of PPU pipes, in comparison with ordinary ones, include:
the ability to install any communications in the shortest possible time and with minimal labor;
reduction in heat loss (usually from 40% to 2%);
a significant increase in the efficiency of pipelines;
increase the life of networks by 2-5 times;
reduction in pipeline repair costs.
Due to the presence of a protective shell, such highways are practically not afraid of the effects of aggressive environments. It is allowed to lay PPU pipelines without grounding and preliminary arrangement of drainage. Polyurethane foam differs, among other things, in that it does not leak moisture. Consequently, steel pipes insulated using this material are much less susceptible to rust.
disadvantages
There are practically no disadvantages of PPU pipes. Perhaps the only drawback of such products is their rather high cost. However, this minus is more than compensated by the long service life of PPU highways and the lack of the need for their frequent repairs.
Mounting Features
PPU pipes are made, thus, from high-quality steel. Therefore, their installation is carried out using welding. Of course, the laying of pre-insulated pipes during the assembly of various industrial and utility networks is carried out according to a special technology. Polyurethane foam - material, unfortunately, does not tolerate too high temperatures. Therefore, when welding such pipes, special protective shields are mandatory.
After connecting the segments of the master, performing the assembly of the PPU line, without fail, check the quality of the joints made. After the metal has completely cooled down at the joints, special couplings are applied to the pipes, among other things. A feature of such structural elements of PPU-highways is that they are made of heat-shrinkable material. After cooling, such a coupling decreases in size and tightly fits the weld, thereby ensuring complete tightness. When using docking elements of this type, a small cavity remains in the joints of the pipes, into which subsequently the mounting foam or polyurethane foam is poured.
The technology described above is used both in the assembly of large industrial highways and small household engineering communications networks.