Seamless steel pipe according to gost 8732 78: products for

Steel thick-walled seamless pipe is most often used for the manufacture of communications experiencing increased operating loads. It is for this reason that the production of such products is regulated by a large number of standards, and finished parts undergo strict quality control.

Below we will review the main legislative recommendations concerning the process of manufacturing seamless pipes, as well as analyze their operational features.

Normative base

Basic standards

To ensure the proper quality of seamless tubular products, all work is carried out in accordance with a number of regulatory documents. In the table below we will list those of which execution is the most important at the moment:

In addition, separate recommendations regulate the production of parts for:

• Fuel lines and oil lines.
• Petrochemical and oil industry.
• Gas pipelines and oil refineries.
• Industrial communications.
• Household and industrial gas pipelines.
• Plumbing systems.
• Shipbuilding, etc.

For each of the above industries, there is a well-defined assortment of seamless steel tubes. However, this information is relevant only for those who are professionally engaged in the design and arrangement of industrial complexes. We should study the nuances of production and the main requirements for pipelines according to GOST.

Varieties of products

Depending on the dimensions of the products, cold-rolled seamless pipes are divided into the following types:

• Particularly thick-walled - the ratio of outer diameter to wall thickness is 6 or less.
• Thick-walled - this ratio is from 6 to 12.5.
• Thin-walled - from 12.5 to 40.

Also provides for the division of products into classes depending on the mechanical characteristics and features of operation:

Production technique

Hot way

Instructions for the manufacture of such products involves the use of complex equipment, because at home a seamless pipe to do, of course, will not work. However, any master should have at least a superficial understanding of the materials with which he works, therefore we recommend that you study the flow charts described below.

Let's start the description with the “hot” technology:

• A cylindrical, square or multi-faceted all-metal bar is used as a blank for the product.. Its material can be different, but most often stainless steel of the corresponding class is used.
• To facilitate the formation of the primary cavity, the workpiece is heated in a furnace. (the temperature must be higher than the temperature at which the recrystallization of the selected steel occurs).

• The liner is being formed - a hollow cylinder. To do this, the workpiece is placed in a piercing mill, where the metal is perforated by means of a very strong pointed rod (firmware) with simultaneous rolling through the gauge rollers.

Note! In the manufacture of large diameter pipes or products with a significant wall thickness, not special machines, but presses are used.

• Then the dross comes off the liner.. Most often this is done using a hydrodynamic installation - in simple terms, the part is treated with water jets under high pressure.
• Further, the product may be subjected to additional heating, but in some cases the material does not have time to cool down until the ductility is lost., therefore, the blank cut is fed to the next operation.

• Here the most important part of machining is performed on the rolling mill - calibration and stretching. At the same time, hardened steel rolls give the pipe the necessary shape and dimensions. The maximum wall thickness of a pipe that can be made using this technique is 75 mm.
• After reducing the dimensions of the product to the design, the parts are cooled, and then subjected to cutting to size, hardening and tempering, if it is provided by GOST.
• Hardened and tempered parts arrive at the quality control stage, where their linear dimensions are analyzed and the main operational indicators are measured..

The further sequence of actions depends on the purpose for which the finished parts will be used. In some cases, threading, screwing in of pipe sleeves and anti-corrosion treatment are included in the process chain. So the products are more convenient to use, but their price increases.

Cool way

Seamless steel pipe according to GOST 8734 - 75 is produced by cold deformation technology.

Here the manufacturing scheme is somewhat different:

• Until the moment of firmware, we do everything the same way as in the case of hot-rolled varieties of pipes: we warm up the blanks, form the sleeve with the help of a piercing mill or a press, etc.

• Then the sleeve is cooled in water with simultaneous descaling.
• At the next stage, the pipe is calibrated by cold rolling. In this case, the rollers stretch and thin the walls until they reach the size we need.
• Further, other operations can be performed, such as annealing (heat treatment), etching with acids, copper plating, applying protective varnishes, etc.

Pipes that are made according to the cold deformation method may have walls no thicker than 24 mm.

Manufacturing Standards

Requirements for hot-rolled products

GOST 8732-78, placed in the title of the article, regulates the manufacture of pipes by the method of hot working.

According to this standard, the following requirements are imposed on products:

• Length - from 4 to 12.5 m. The length can be both unmeasured and measured.

Note! It is allowed to manufacture products with dimensions that are multiple to dimensional, with an allowance of 5 mm in length for each cut.

• The allowable deviation from the design dimensions in length is 10 mm for products up to 6 m, and 15 mm for pipes over 6 m long.

Limit deviations from the outer diameter are also regulated:

• With a nominal diameter of up to 50 mm - no more than 0.5 mm upwards or downwards.
• With a diameter of up to 219 - 1 mm with conventional precision manufacturing and 0.8 - with increased.
• More than 219 - 1.25 and 1 mm, respectively.

As for the tolerances in the wall thickness, they also depend on the diameter and can be from 10 to 15% of the nominal value.

The curvature requirements are as follows:

• For pipes with wall thickness up to 2 cm - not more than 1.5 mm per 1 running meter.
• For products from 2 to 3 cm - no more than 2 mm per 1 m.
• 3 cm and above - no more than 4 mm.

The range according to GOST for seamless steel pipes of hot deformation includes a variety of products. Below we present only those that are used most actively:

Standards for the production of cold pipes

Requirements for pipes produced by rolling chilled billets are governed by GOST 8734 - 75:

• Measured length - from 4.5 to 9 m.
• The maximum deviation in size for pipes of measured length is + 10 mm.
• Unmeasured length - from 1.5 to 11.5 m.
• The allowance for the cut product - 5 millimeters.

Indenting outer diameter:

• For pipes from 4 to 10 mm -0.15 mm upwards or downwards.
• For products 10-30 - 0.3 mm.
• 30-50 - 0.4 mm.
• More than 50 - 0.8 mm.

Control of wall thickness is carried out on the basis of such data:

• Pipes with a wall of 1 mm or less - a deviation of 0.12 mm is allowed.
• Wall 1-5 - no more than 10% of the nominal thickness.
• A wall over 5 - no more than 8%.

Curvature tolerances are also fairly strict:

• For parts with a section from 4 to 8 mm - 3 mm per linear meter.
• For pipes up to 10 mm - 2 mm per 1 m.
• Over 10 mm - 1 mm per 1 m.

As for the range, it is also very extensive. At the same time, groups of products with different wall thickness are clearly separated:

Main advantages and disadvantages

Rolled products that are manufactured using seamless technology have a number of operational advantages.

Below we will analyze those of them that are most relevant to the masters who carry out the installation of communications with their own hands:

• The absence of a weld in the part wall is rightly considered to be its main advantage. Since the material has a monolithic structure, it does not form areas of internal stress that are potentially dangerous to the integrity of the product. So, the seamless pipe copes much better with increasing internal pressure, effectively compensating for pressure surges.

• The use of carbon and high-alloy steels contributes to an increase in corrosion resistance. Such pipes tolerate even prolonged contact with aggressive chemicals, and the wall material does not lose its properties.

Note! This is true only if the technological production cycle was organized in accordance with all the requirements of GOST. Thus, the quality of quenching, tempering and etching of parts has a significant effect on the material's resistance to external influences.

• The use of steel with the addition of molybdenum, chromium and other materials contributes to improving the heat resistance of the product. Pipes are able to cope even with very strong heating, which allows them to be effectively used at extreme temperatures.

• An additional effect of increasing the heat resistance is to reduce the temperature deformation of the pipe: the system turns out to be quite stable, which makes it possible to effectively perform its concealed installation without fearing the destruction of the finish.
• Another advantage is a very extensive assortment. The above tables were given with the ratio of the diameter of the pipes and wall thickness, but it must be remembered that they contain only the most popular sizes. In practice, you can find a pipe for almost any section.

As for the minuses, they are very conditional:

• First, for products with thick walls often characterized by a significant mass. This imposes quite definite restrictions on the designer, since the bearing characteristics of the structure must cope with the load.
• Secondly, the flexibility of most pipes is very low. Usually this does not create problems, but when laying a pipeline or repairing it, difficulties may arise with the installation of nozzles in hard-to-reach areas. However, issues of this nature are usually solved at the design stage.
• Finally, the question of the cost of products, too, can not be called unambiguous. High quality seamless pipes are quite expensive material, but often the performance requirements do not leave us a choice: we have to buy them. On the other hand, the high cost is compensated by reliability and durability.

Conclusion

GOST for seamless steel pipes of cold and hot rolling must be strictly followed. Only in this case, the products will meet high quality standards, and will be able to cope with high operating loads. The video in this article contains a number of additional information about such products, so that craftsmen working with pipelines should carefully study it.