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Today communications from polymeric materials have forced out the majority of metal analogs. However steel remains also now widespread alloy of which pipelines are manufactured. One of the main characteristics of steel pipes having impact on operational accessory – diameter. This indicator is obligatory by drawing up construction schemes.

## Types of steel pipes on way of their production

Steel pipes are used when laying water supplies and gas transmission communications. Such products have set of merits from which it is possible to distinguish high strength, resistance to longitudinal expansion. Essential lack of such products is that they have weak resistance to corrosion influences. All steel pipes are classified by way of production and assignment.

One of the most widespread kinds of steel pipes are electrowelded products. They are also called straight-line-seam. Are carried out from sheet steel. Application of electrowelding equipment allows to receive small equal seam. Such pipes are used when laying water communications and gas transmission systems. It is quite simple to determine diameters of pipelines of this kind by normative documentation. Range of the sizes of section in this case is 10-1420 mm.

The following kind of steel pipes – spiral. Such products are made of steel which is produced in rolls. As well as the previous type, these parts have seam, however it does not differ in the minimum width. Thus, spiral pipes are not capable to maintain high rates of pressure (unlike electrowelded). Because of it they are not applied to laying of gas transmission systems.

The modern industry allows to release designs which have no seam at all. Seamless pipes are carried out from special preparations. It should be noted that such products are made in two ways: hot and cold.

Range of diameters of products which have no seam fluctuates ranging from 10 up to 550 mm. The lack of seam considerably increases strength characteristics of these pipes that allows to use them in responsible communications.

Pay attention! Normative documentation exercises control of seamless products, however it extends only to parts which diameter does not exceed 250 mm.

## Diameters of steel pipes: for what these indicators and as they are defined are necessary

Knowing exact value of diameter which the water or gas pipe has, there is possibility of calculation of volume of the substance transported on communications. Use of such pipes in construction demands accurate definition of the dimensional characteristics necessary for calculations of economic systems.

It is possible to give heating system as example. Diameter of pipes in such communications has to be accurately calculated in order that during the winter period the system provided uniform warming up of premises.

Today there are several widespread methods allowing to calculate diameter of steel pipes. The size table which can be found in the regulating documentation is the simplest of them. It is also possible to determine this parameter by online calculators. Such programs are on the profile websites in network therefore it is possible to find them.

Independent calculation of diameter of communication is made by means of mathematical expressions. The type of formula depends on operational assignment of communication. For example, apply the following equation to determination of diameter of heating pipe:

**D = sqrt ((3.14 x Q) / (V x DT)), where:**

- D – diameter (internal);
- Q – the indicator of heat flux calculated in kW;
- V – speed of the substance transported on the pipeline (it is measured in m/s);
- DT – the difference of temperatures in the initial and final point of system (input and output);
- sqrt – square root.

The similar formula allows to define pipe diameter quite precisely. Designation of this indicator in schemes gives the chance to correctly calculate the required pressure and amount of the transported substance for unit of time.

## What diameters of pipes exist: their versions

Today diameters are subdivided into several types depending on what is characterized by this size. For use of this parameter in calculations it is recommended to study types of diameters.

Conditional pass of pipes (DN). Indicator of internal space of pipe. This parameter is calculated in mm or inches. In the second case rounding of size is made. Knowledge of this parameter allows to select accessories (fitting) of the necessary size to pipes.

Nominal diameter. This indicator very much reminds the previous type, however has some differences. For example, the main characteristic of nominal parameter is its high accuracy which does not suffer roundings.

Inside diameter (Du). This indicator is the physical quantity which is measured in mm. Inside diameter is used at calculations of passability of pipeline design. You should not confuse this size with the nominal diameter of pipes.

Pay attention! For calculation of this parameter there is special formula: Dy = Dn — 2S.

Outside diameter (Dn). In this parameter all pipes made of steel are subdivided into 3 main groups: small, average and big. Each group has own range of the sizes and the assignment. It is the simplest to determine this indicator by the table of steel pipes.

It should be noted such parameter as wall thickness. This size belongs to physical and has impact on qualitative characteristics of part. For example, the volume of product and its weight depend on wall thickness. Wall thickness in mm is calculated.

**For its definition often use the following simple formula:**

- T = Dn — Du

## Systems of measurement of diameters of pipes: table (inches and millimeters)

Products which diameter is calculated in inches (for example, 5 ″) are used when laying water communications and gas transmission designs. On the Internet it is possible to meet the tables containing this size both in millimeters, and in inches. Some of schemes combine in themselves both systems of measurement that is very convenient. The five-inch pipe corresponds to standard indicator of inside diameter, equal 125 mm.

Measurement of diameter of pipes in inches is applied during mounting of water transport and gas transmission lines as it simplifies the general calculation. One inch is equal to 25.4 mm. It is important to remember that at measurement of pipe 1 inch has other size, namely 33.5 mm. It speaks quite simply: dimensions of pipes are calculated on inside diameter, but not on external. By drawing up the mounting plan and scheme it is necessary to consider this discrepancy. Similar information allows to answer question of how to measure pipe diameter and not to make at the same time mistake.

Useful information! As a rule, no problems arise when mounting only of steel articles as they are measured in inches. However at emergence of need of replacement of old communication from steel on plastic there can be confusion. Therefore it is worth remembering that the actual and metric sizes of inch differ.

In most cases laying of inch pipes does not cause any difficulties. The nature of discrepancy consists in designation of steel articles (water and pipeline) which are implemented and marked by the nominal diameter while their actual section has other sizes. It is possible to give simple calculation of dimensions of pipe which outside diameter is 140 mm, and wall thickness – 5.5 mm as example.

**For determination of actual diameter the simple equation is used:**

- D = Dn – t x 2

After implementation of the necessary values this formula takes the following form: D = 140 – 5.5 x 2 = 129 mm. This indicator corresponds to real pipe diameter at which the section of outside wall is 140 mm. However conditional pass or inside diameter of inch pipe (or millimetric) is the predominating value. In this case this size is 125 mm, in it the majority of construction calculations is made.

For joining of steel and plastic pipes special transitional elements – fitting are used. Similar adapters allow to connect two pipes with different indicators of section made of different materials. Not to be mistaken when mounting communication or its replacement, it is recommended to consider both external, and internal diameters of steel pipes.

## Outside diameter of pipes (Dn): classification of steel articles

As already it has been told above, internal and outside diameters differ from each other. The first of them is used at designation of separate elements of pipeline designs. Implementation of steel articles is also carried out on inside diameter. This indicator is important if it is necessary to carry out mounting calculations of water supply system or the gas line. In turn, outside diameter is used for definition of strength pipeline characteristics and its resilience to mechanical loadings.

Outside diameter of steel pipes – characteristic by which all products from this material are classified.

**Depending on this parameter allocate three main kinds of pipelines:**

- small;
- averages;
- big.

Pipes which belong to group of small have the range of diameters from 10 to 102 mm. Products of the average size can have section from 102 to 426 mm. Range of diameters of big steel pipes begins from 426 mm. In turn, determination of inside diameter is recommended to be done according to the table.

Small pipes are used when mounting communications in inhabited constructions. By means of average products city water transport lines are laid and also they are actively exploited by the companies which are engaged in oil production (crude). The main spheres in which big products from steel have found application are oil transmission and gas transmission areas. From big parts collect through lines. Diameter of gas pipes can reach 1220 mm.

## Standard diameters of steel pipes: table and description

When finding inside diameter the indicator corresponding to the amount of conditional pass is rounded to 0 or 5. Thus, when determining this characteristic there is standardization of the size to the closest parameter of the metric system.

Knowing this information, it is simpler to carry out calculation of pipe diameter. As this parameter is measured in millimeters and inches, already it has been told above.

Pay attention! Products with a diameter from 426 to 1220 mm have the greatest distribution caused by operational suitability. Data of pipe from steel are applied as through lines to gas pipelines and oil pipelines, sewerages and also designs used for irrigation of fields.

In residential buildings apply steel water pipes which diameter is 15 or 20 mm (sometimes 32). For the sewerage more dimensional products are used that is caused by need of withdrawal of drains. Heating systems consist of small pipes.

Normative documents contain more detailed tables which contain information not only on section, but also on other geometrical characteristics. It is the simplest to determine diameter of pipes by them (in millimeters and inches). It is important to remember that by means of application of special tables it is possible to calculate necessary indicator of section (internal or outside) both steel, and other kinds of pipes.

## Finding of diameter of steel pipes: the table with thickness

Use of the special tables which are located in normative documentation allows to determine necessary parameter very quickly. It can be inside or outside diameter and also auxiliary geometrical characteristics, such as wall thickness, weight, etc. are specified.

It should be noted that the difference between the outside diameter of metal pipes and Du can reach 7 mm (depending on kind of metal rolling). For example, the steel electrowelded components used when mounting economic communications can differ on these indicators on 5-10 mm.

The key indicator indicating product accessory, certainly, is inside diameter. Pipes are also designated by the outside size of section which is necessary condition when calculating mechanical resistance.

Pay attention! The sizes of the products having inch marking the easiest are defined by means of tabular method. It is important to remember that when joining lines from steel with pipelines from other material (for example, plastics) it is necessary to take in attention not only Du, but also Dn.

The popularity of tabular method is caused by the fact that the combined pipeline designs are widespread in the modern world. Such systems comprise steel pipes and polymeric elements (fitting).

## Table of steel pipes: diameters, the price for meter

The cost of one meter of data of products is determined by their weight. In this case certain dependence is traced: the product from steel, the more its weight is thicker. It is possible to find set of tables which contain information on the prices of the different parts classified by inside diameter in the Internet. Steel pipes belong to mid-price segment. They are more expensive polymeric, however exceed them on durability and resilience to pressure.

It should be noted that for production of steel pipes different alloys and protective additives can be used. It also has impact on the final cost of products. For example, galvanized parts or pipes from stainless steel have higher price, than the elements made of normal steel.

Thus, diameter of water pipes and gas transmission products has impact on their cost. Parts which have section over 100 mm are practically not used in life. The cost of such pipes is quite high as 1 m of part can weigh more than 10 kg. The heaviest pipe has diameter of 1220 mm and thickness of wall of 16 mm. The weight of meter of such part is about 475 kg.

Diameter – necessary characteristic without which laying of pipeline design is impossible. When determining this parameter it is necessary to understand accurately that there are several its versions. In tables which can be found in the corresponding normative documentation the inside diameter of steel articles most often is specified. If you have decided to use special formula for determination of section, it is recommended to pay attention to the examples containing the decision.