Temperature coefficient of linear expansion of steel

Linear extension of pipelines

13.12.2018

When planning the installation of a pipeline, it is necessary to take into account the coefficient of linear expansion of the material (LEC). This is a physical quantity that reflects the change in body size with increasing temperature (by 1K) and constant pressure. The materials from which the pipes are made have fixed linear expansion values, which simplifies the design.

Carbon steels

The table shows the values ​​of the linear expansion coefficient of carbon steel in the temperature range from -173 to 1000°C. When such steel is heated, its TCLE increases and can reach 19.8·10-6 deg-1 (for U8 steel) in the temperature range 27-650°C.

Since carbon steel consists almost entirely of iron and does not contain nickel or chromium additives, its thermal expansion coefficient is largely determined by the coefficient of linear expansion of this main component.
For example, the maximum coefficient of linear expansion of steel 20, like that of iron, is 14.8·10-6 deg-1 in the temperature range from 27 to 700°C. Linear expansion coefficients of carbon steel

PEX pipe joining method

PEX pipe products are produced from different types of cross-linked polyethylene and differ in their characteristics. Types of markings:

1. RE-Ha. Cross-linked using the peroxide method. Uniform structure with the largest number of cross-linked molecules, durable and safe for human health.
2. PE-Xb. Crosslinked using the silane method. No less durable products than peroxide polyethylene pipes, but more rigid and less able to restore their original shape. Some varieties contain chemicals and are intended only for the manufacture of cable sheaths. Therefore, when choosing water pipes, you need to be guided by the data in the hygiene certificate;
3. PE-Xs made from radiation cross-linked polyethylene are more rigid, prone to creases and are inferior in structure uniformity to peroxide materials.

Chromium-nickel low- and medium-alloy steels

The table shows the temperature coefficients of linear expansion of low- and medium-alloy chromium-nickel steels of common grades at temperatures from -268 to 1000°C.

The highest TCLE of the grades considered in the table is possessed by chromium-nickel steel 12Х2Н4А and 12ХН3А, which in the range of 27-600°С is equal to 15.6·10-6 deg-1.
Linear expansion coefficients of chromium-nickel steel

Chrome steels

Chromium steels have a coefficient of linear expansion on average from 10 to 13·10-6 deg-1.
Additionally, it is worth noting steel ShKh15 and 40Kh, the value of TCLE of which is 13.4...15.7·10-6 deg-1. Linear expansion coefficients of chromium steel

Connection methods

Polyethylene pipes are connected in three ways:

1. Compression fittings. Compression-type fittings are easier to install and can be used to assemble cold and hot water supply pipelines.
2. Press fittings. With the help of press fittings, permanent joints of parts are obtained. Due to the property of the material to restore its shape after deformation, the polymer molecules in the joint area straighten after crimping and fill all the gaps between the pipe and the connecting elements. The result is a pipeline with very reliable connections that do not require additional maintenance.
3. Electric welded couplings. The electric welding method promotes the formation of monolithic joints that are not inferior in strength to the product itself.

Chrome-nickel steels with nickel content up to 20%

The table shows the linear expansion coefficients of chromium-nickel steels with a nickel content of up to 20%.
This type of steel includes a significant variety of grades that have a wide range of thermal expansion coefficients - from 8 to 17.5 10-6 deg-1 at temperatures up to 100°C and from 10 to 24.6 10-6 deg-1 in the range up to 1000°C. Linear expansion coefficients of chromium-nickel steel with nickel content up to 20%

Chemical resistance of polyethylene

The polyethylene in the product has good resistance to various aggressive chemicals: nitric acid of various concentrations, ammonia (gaseous, dry, 100%, pure, aqueous solution, saturated in the cold), technical acetone, gasoline, tartaric acid, any wine, water (distilled, demineralized, demineralized, mineral, sea), potassium salts, compressed air containing oils, copper and magnesium salts, waste gases of sewage systems, etc., containing carbon dioxide, hydrochloric acid, sulfur dioxide, mercury, hydrogen sulfide, sulfur , urea, soap solution, etc.

Chrome-nickel steels and alloys with a nickel content of more than 20%

Chromium-nickel steels with a nickel content of more than 20% have a linear temperature expansion coefficient of up to 19.8·10-6 deg-1 (alloy KhN46B).
The steel of this type with the lowest TCLE value is 04ХН40МДТУ; its average linear expansion coefficient at temperatures up to 100°С is 8.2·10-6 deg-1. Linear expansion coefficients of chromium-nickel steel with a nickel content of more than 20%

Manganese and chromium-manganese steels

The table presents the average values ​​of the coefficients of thermal linear expansion of manganese and chromium-manganese steels in the temperature range from -269 to 1000°C.
It should be noted that 30KhGSA steel has the minimum TCLE at high temperatures. Linear expansion coefficients of manganese and chromium-manganese steel

Chrome-molybdenum steels

Chromium-molybdenum steels, compared to other types, have relatively low TCLE values.
The linear expansion coefficients of steel of this type are 9.7...15.5·10-6 deg-1 at temperatures up to 1000°C. Linear expansion coefficients of chrome-molybdenum steel

Chrome tungsten and chrome vanadium steels

The table shows the average linear expansion coefficients of chrome-tungsten and chrome-vanadium steels for the temperature range from 27 to 1000°C.
The table shows that these types of steel have similar TCLE values. Linear expansion coefficients of chrome-tungsten and chrome-vanadium steel

Tips on how to choose

The selection of pipes should begin with a visual inspection. They must have a smooth surface. Slight waviness and the presence of longitudinal stripes are acceptable provided that they do not thicken the wall beyond the permitted values. In addition, the pipes must have a uniform color, and the surfaces must be free of cracks, bubbles, foreign inclusions, and cavities.

Information on the main characteristics of pipes is included in the marking. From it you can find out what type of stitching was used in manufacturing, as well as the geometric parameters of the product.

Popular manufacturers

Pipe products from the following brands have proven well:

1. TECEflex (Germany). The company produces pipes of the PE-Xs brand. Crosslinking is carried out by the electron beam method. Ethylene vinyl alcohol is used for anti-diffusion protection. It forms an oxygen-blocking layer that is resistant to mechanical damage.
2. UNIDELTA (Italy). Manufactures pipes with an internal protective layer of EVOH, cross-linked using the silane method.
3. REHAU (Germany). The company produces products from peroxide polyethylene with an external anti-diffusion coating, painted red.

approximate price

Materials made from cross-linked polyethylene are cheaper than polypropylene products, which are also used for assembling plumbing and heating systems. The cost of PEX pipes depends on the method of cross-linking polyethylene.

Chromium-cobalt steels and alloys

Chromium-cobalt steels have a temperature coefficient of linear expansion of 12...17.7·10-6 deg-1 at temperatures up to 300°C and 15.5...17.8·10-6 deg-1 at high temperatures.
Of particular note is steel 40K44Kh20N20M4V4B4, the average expansion coefficient of which practically does not change in the range from 300 to 1000°C. Coefficients of linear expansion of chromium-cobalt steel

Silicon, titanium and other steels and alloys

The table contains the values ​​of the average linear expansion coefficient of titanium, silicon and other steels and alloys in the temperature range from 27 to 1000°C.
The steel types considered have a relatively low TCLE, which, for example, for E16 steel is only 7·10-6 deg-1 at a temperature of 27-100°C. Linear expansion coefficients of silicon, titanium and other steels and alloys

Sources:

1. Novitsky L.A. Thermophysical properties of materials at low temperatures.
2. Physical properties of steels and alloys used in energy. Directory. Ed. Neymarka B.E. M.-L.: Energy, 1967.
3. Tables of physical quantities. Directory. Ed. I.K. Kikoina. M.: Atomizdat, 1976.
4. Kuzminov Yu.S. Ferroelectric crystals for controlling laser radiation. M.: Nauka, 1982.
5. Solntsev Yu.N., Stepanov G.A. Materials in cryogenic technology. Directory. L.: Mechanical Engineering, 1982.
6. Pridantsev M.V. etc. Structural steels. Directory. M.: Metallurgy, 1980.
7. Ulyanin E.A., Sorokina N.A. Steels and alloys in cryogenic technology. Directory. M.: Metallurgy, 1984.

Kinds

The material is divided into types depending on the method of stitching:

1. Peroxide. Cross-linked with hydrogen peroxide. The process takes place under pressure and covers up to 85% of the molecules.
2. Silane. Chemically cross-linked, when the raw material is saturated with organic silanides and hydrated. The resulting polymer has up to 70% cross-linked structure.
3. Radiation. During cross-linking, the polymer is exposed to the energy of ionizing radiation. The proportion of linked molecules is up to 60%.
4. Nitric. Nitrogen compounds are used for crosslinking. The structure of polyethylene with this method is 70% cross-linked.