Stainless steel is a material that is particularly resistant to corrosion. Pipes made from it can last for decades even when exposed to an aggressive environment. In addition, stainless steel products have an attractive appearance. But in order to take full advantage of these advantages, you need to know the types of any stainless pipes, their main dimensions and characteristics.
Properties of stainless steel pipes
The main requirement for all steel grades in this category is a high content of chromium in it. The minimum content of this metal is regulated at 12%. It creates a special film on the surface of the product that protects the material from external influences. It also contributes to the fact that the medium pumped through the pipeline is also not subject to changes. This is especially important for drinking water and food mains.
Inexpensive steel grades are limited only by the presence of chromium. They differ in plasticity and resistance to deformations. To give special strength and resistance to corrosion, molybdenum, nickel, titanium and other alloying additives are added to the composition.
In addition to chromium, the presence of sulfur and its compounds in steel is also regulated. It is believed that their maximum content should not exceed 0.02%.
The surface of stainless steel profiles can be polished on special machines to a mirror state. This not only gives an attractive appearance, but also creates additional protection against sources of corrosion. Despite the increased price of polished products, they are in demand as a design element.
Classification of stainless steel pipes
According to the shape of the internal section, they distinguish:
- square and rectangular.
Corrugated options are considered a separate class. They are characterized by special plasticity and the ability to undergo repeated cycles of compression and tension both in the longitudinal and transverse directions.
With various methods of manufacturing stainless steel, they may differ in the presence or absence of a seam on the finished product. According to this parameter, pipes are distinguished:
- straight seam,
- spiral stitch.
The production of solid profiles is carried out without the use of welding, by rolling on special blanks. Such products have increased tensile strength and are able to withstand significant loads. Therefore, they are used in pipelines with high pressure or where special reliability is required.
The method of manufacturing without seam formation leads to an increase in the cost of the output product. It is unprofitable to use these products in the domestic sphere.
Production and standard sizes of seamless stainless pipes are regulated by GOST 9940-81 and 9941-81.
Straight seam welding
The blanks for this technology are steel sheets. They are bent on special presses into a circle of the required diameter. The edges of the sheets at the junction are welded together to form a seam running along the entire length.
Welding methods can be different, but the main one is electric welding.
The parameters and requirements for the production of straight-seam stainless steel pipes are set out in GOST 11068-81.
Spiral stitch technology
The production is also based on the welding of bent steel sheet. But the joining of the edges does not go in a straight line, but in a spiral covering the entire length.
Such a seam is considered more durable, since it excludes the formation of longitudinal cracks. But its total length is greater than in the straight-line version. This also leads to higher welding costs.
The production of spiral pipes is regulated by GOST 8696-74.
Degree of heating
According to the methods of heat treatment in the manufacture of stainless products, there are:
- cold worked method. Made without heat. If necessary, heat treatment of the finished product is carried out.
- Thermally deformed. When forming a profile, the workpiece is subjected to slight heating.
- Hot-formed. The pipe is formed from steel heated to a red-hot state.
The cold method is more complicated, but gives the finished products greater strength. Therefore, cold-formed pipes are produced with a smaller wall thickness than those made using hot technology.
The differences between the standards governing the production of seamless pipes are precisely in the temperature regime during manufacture. GOST 9940-81 is intended for the hot-worked method, and GOST 9941-81 is for cold and heat-worked production.
In addition to this value itself, there is an indicator showing the ratio of diameter to wall thickness. The larger it is, the thinner the product is considered. This parameter is denoted SDR.
There are the following categories:
- especially thin-walled — SDR > 40;
- thin-walled — SDR = 13 — 40;
- thick-walled — SDR = 6 — 13;
- especially thick-walled – SDR < 6.
Depending on the additional surface treatment after manufacture, three types of pipes are distinguished:
- Matte. Only bumps and burrs are removed.
- Sanded. The material is only subjected to initial grinding using fine-grained abrasives.
- Polished (mirror). Finishing the surface after grinding to the final gloss. There are methods of mechanical, chemical and electrolytic polishing.
Applications of stainless pipes
The corrosion resistance of such products determines their use in pumping aggressive media and in particularly critical sections of conventional pipelines. And the lack of contact with the pumped substance allows them to be used in the food industry.
The beautiful appearance of the polished surface is used in the design of residential and industrial premises.
It is possible to create street structures from stainless profiles.
Determining the weight of a running meter
For large batches of pipe products, prices are indicated by weight — per ton. It is more convenient, since the assortment of pipes is reduced. The price of metal of the same quality does not depend on the diameter and wall thickness. Only in retail trade and for household purposes, the cost is calculated based on the length in meters.
To recalculate prices, you need to know the weight of 1 linear meter of pipe with the required characteristics. Required data for calculations:
- material density,
- diameter (and for rectangular sections — length and width)
- wall thickness.
For plumbing products, the diameter is often indicated in inches. The correspondence is something like this:
- 1/2 inch = 15mm
- 3/4 = 20 mm
- 1 inch = 25mm
The specific densities of the most common steel grades are shown in the table in the figure:
It turns out that the difference between the minimum and maximum values does not exceed 3%. Therefore, an accurate density value is only required when calculating large batches. For normal calculations, it is enough to substitute the average number — 7850 kg / m3.
The weight of a linear meter of a stainless pipe of circular cross section is calculated by the formula Р= S*h*T, where:
- S — surface area \u003d 3.142 * outer diameter of the pipe;
- h is the wall thickness;
- T is the specific gravity.
The weight of 1 meter of rectangular and square profiles is even easier to determine. The perimeter of the section (twice the sum of the width and height) is multiplied by the wall thickness and by the specific gravity.
Diameters and walls of stainless pipes size chart. Part 1.
|D, mm||Wall thickness, mm|
|Weight of 1 linear meter, kg|
Table. Part 2
The cost of a stainless pipe depends on many parameters: steel grade, the presence or absence of a seam, and the method of manufacture. For household pipes of small diameter, the quality of surface grinding also affects.
Therefore, it is worth considering only some differences in individual characteristics.
Prices per kilogram (ton) are weakly dependent on the diameters and walls of a particular pipe. The difference usually does not exceed 10-20%.
The grade of steel from which the pipe is made has a much stronger effect on the cost. With other identical characteristics, the price varies significantly. So, steel 12X13 costs 180 — 200 rubles / kg, and exactly the same pipe, but from the brand 08X18H10T 330 — 350 rubles / kg.
Comparison by production methods:
- A seamless pipe made of steel grade 08X18H10T, manufactured by the cold-formed method, costs about 330 rubles / kg.
- The price for hot-formed production will be 90 — 120 rubles / kg.