# Steel pipe diameters: how to plan communications correctly

Steel pipe diameters: how to plan communications correctly

Today, communications made of polymer materials have displaced most metal analogues. However, steel still remains a common alloy from which pipelines are made. One of the main characteristics of steel pipes that affects the operational affiliation is the diameter. This indicator is mandatory when drawing up building schemes. The diameters of steel pipes are regulated by the relevant GOST standards.

## Types of steel pipes according to the method of their production

Steel pipes are used in laying water supply systems and gas transmission communications. Such products have many positive qualities, among which one can distinguish high strength, resistance to linear expansion. A significant disadvantage of such products is that they have poor resistance to corrosion. All steel pipes are classified according to the method of manufacture and purpose.

One of the most common types of steel pipes are electro-welded products. They are also called straight-seam. They are made of sheet steel. The use of electric welding equipment allows you to get a small smooth seam. Such pipes are used in laying water utilities and gas transmission systems. The diameters of pipelines of this type are quite easy to determine with the help of regulatory documentation (GOST 10704-91). The cross-section size range in this case is 10-1420 mm.

The next type of steel pipes is spiral pipes. Such products are made of steel, which is produced in rolls. Like the previous type, these parts have a seam, but it does not differ in the minimum width. Thus, spiral-welded pipes are not able to withstand high pressure values (unlike electric-welded ones). Because of this, they are not used for laying gas transmission systems. These products are regulated by GOST 8696-74.

Modern industry allows us to produce designs that do not have a seam at all. Seamless pipes are made of special blanks. It is worth noting that such products are made in two ways: hot and cold. In GOST, the diameters of steel pipes are prescribed in special tables containing other geometric characteristics of products, which simplifies the search. Seamless parts are regulated by GOST 8732-78 and GOST 8734-75.

The diameter range of products that do not have a seam ranges from 10 to 550 mm. The absence of a seam significantly increases the strength characteristics of these pipes, which allows them to be used in responsible communications.

Pay attention! Regulatory documentation controls seamless products, but it applies only to parts whose diameter does not exceed 250 mm.

## Steel pipe diameters: why these indicators are needed and how they are determined

Knowing the exact value of the diameter that a water or gas pipe has, it becomes possible to calculate the volume of the substance transported through communications. The use of such pipes in construction requires a clear definition of the dimensional characteristics necessary for the calculations of economic systems.

An example is the heating system. The diameter of pipes in such communications should be clearly calculated so that in winter the system provides uniform heating of residential premises.

To date, there are several common methods for calculating the diameter of steel pipes. The size chart, which can be found in the regulatory documentation, is the simplest of them. You can also determine this parameter using online calculators. Such programs are located on specialized sites on the web, so it is not difficult to find them.

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

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

D – diameter (internal);

Q is the heat flow indicator, calculated in kW;

V is the velocity of the substance transported through the pipeline (measured in m/s);

DT – temperature difference at the start and end point of the system (input/output);

sqrt is the square root.

Such a formula allows you to fairly accurately determine the diameter of the pipe. The designation of this indicator in the diagrams makes it possible to correctly calculate the required pressure and the amount of transported substance per unit of time.

### What pipe diameters exist: their varieties

Today, diameters are divided into several types, depending on what exactly characterizes this value. To use this parameter in calculations, it is recommended to study the types of diameters.

Conditional passage of pipes (DN). An indicator of the internal space of the pipe. This parameter is calculated in mm or inches. In the second case, the value is rounded. Knowledge of this parameter allows you to select components (fittings) of the right size for pipes.

Nominal diameter. This indicator is very similar to the previous type, but it has some differences. For example, the main characteristic of a nominal parameter is its high accuracy, which does not tolerate rounding.

Inner diameter (Dy). This indicator is a physical quantity that is measured in mm. The inner diameter is used to calculate the patency of the pipeline structure. Do not confuse this value with the nominal diameter of the pipes.

Pay attention! There is a special formula for calculating this parameter: Dy = Dn — 2S.

Outer diameter (Dn). According to this parameter, all pipes made of steel are divided into 3 main groups: small, medium and large. Each group has its own size range and its own purpose. The easiest way to determine this indicator is by the table of steel pipes. GOST standards regulating such products can be easily found on the Internet using the search bar of your browser.

It is necessary to note such a parameter as the thickness of the walls. This value refers to the physical and affects the quality characteristics of the part. For example, the volume of the product and its mass depend on the thickness of the walls. The wall thickness is calculated in mm. To determine it , the following simple formula is often used:

t = Dn — Dy

## Pipe diameter measurement systems: table (inches and millimeters)

Products whose diameter is calculated in inches (for example, 5″) are used for laying water utilities and gas transmission structures. On the Internet, you can find tables containing this value in both millimeters and inches. Some of the schemes combine both measurement systems, which is very convenient. A five-inch pipe corresponds to a standard internal diameter of 125 mm.

Measuring the diameter of pipes in inches is used during the installation of water and gas transmission lines, as this simplifies the overall calculation. One inch is equal to 25.4 mm. It is important to remember that when measuring a pipe, 1 inch has a different size, namely 33.5 mm. This is explained quite simply: the dimensions of the pipes are calculated by the inner diameter, and not by the outer. When drawing up the installation plan and scheme, it is necessary to take into account this discrepancy. Such information allows you to answer the question of how to measure the diameter of the pipe and avoid making mistakes.

Table 1. Dd in millimeters and inch steel pipe size designation system:

Dy, mm | Thread diameter, inches |

150 | 6″ |

40 | 1 1/2″ |

80 | 3″ |

15 | 1/2″ |

100 | 4″ |

32 | 1 1/4″ |

50 | 2″ |

125 | 5″ |

25 | 1″ |

Useful information! As a rule, no problems arise when installing only steel products, since they are measured in inches. However, if there is a need to replace the old steel communication with plastic, confusion may occur. Therefore, it is worth remembering that the actual and metric inch sizes are different.

In most cases, laying inch pipes does not cause any difficulties. The nature of the discrepancy lies in the designation of steel products (water and gas pipelines), which are sold and marked with a nominal diameter, while their actual cross-section has other dimensions. As an example, a simple calculation of the dimensions of a pipe with an outer diameter of 140 mm and a wall thickness of 5.5 mm can be given.

A simple equation is used to determine the actual diameter:

D = Dn – t x 2

After the introduction of the necessary values, this formula takes the following form: D = 140 – 5.5 x 2 = 129 mm. This indicator corresponds to the actual diameter of the pipe, which has a cross-section of the outer wall of 140 mm. However, the conditional passage or the inner diameter of an inch pipe (or millimeter) is the dominant value. In this case, this value is 125 mm, it is according to it that most construction calculations are made.

Special transition elements – fittings are used for joining steel and plastic pipes. Such adapters allow you to connect two pipes with different cross-section indicators made of different materials. In order not to make a mistake when installing communication or replacing it, it is recommended to take into account both external and internal diameters of steel pipes.

## Outer diameter of pipes (Dn): classification of steel products

As mentioned above, the inner and outer diameters differ from each other. The first of them is used when designating individual elements of pipeline structures. The realization of steel products is also carried out according to the inner diameter. This indicator is important if it is necessary to carry out installation calculations of a water pipe or a gas line. In turn, the outer diameter is used to determine the strength characteristics of the pipeline and its resistance to mechanical loads.

The outer diameter of steel pipes is a characteristic by which all products made of this material are classified. Depending on this parameter , there are three main types of pipelines:

- small;
- medium;
- big.

Pipes that belong to the small group have a diameter range from 10 to 102 mm. Medium-sized products can have a cross-section from 102 to 426 mm. The diameter range of large steel pipes starts from 426 mm. In turn, it is recommended to determine the inner diameter according to the table.

Small pipes are used in the installation of communications in residential buildings. By means of medium-sized products, urban water transport lines are laid, and they are also actively exploited by companies that are engaged in the extraction of oil (crude). The main areas in which large steel products have found application are the oil and gas transportation areas. Trunk lines are assembled from large parts. The diameter of gas pipes can reach 1220 mm.

### Standard diameters of steel pipes: table and description

When the inner diameter is found, the indicator corresponding to the dimensions of the conditional passage is rounded to 0 or 5. Thus, when determining this characteristic, the size is standardized to the nearest parameter of the metric system.

Related article:

GOST standards of steel pipes: the main standards of quality products

Different types of metal products. Varieties of pipes. Manufacturing methods. Technical characteristics of steel pipes according to the standard.

Knowing this information, it is easier to calculate the diameter of the pipe. How this parameter is measured in millimeters and inches has already been mentioned above.

Pay attention! The most widespread, due to operational suitability, are products with a diameter from 426 to 1220 mm. These steel pipes are used as main lines for gas and oil pipelines, sewers, as well as structures used for irrigation of fields.

In residential buildings, steel water pipes are used, the diameter of which is 15 or 20 mm (sometimes 32). For sewerage, larger products are used, which is due to the need for drainage of drains. Heating systems consist of small pipes.

Table 2. The impact of diameter on the operational sphere:

Operational scope | Diameter, mm |

Water pipes in residential buildings | 15-32 |

Gas pipelines in residential buildings | |

Sewage systems | 50-100 |

Gas and oil transportation lines | 426-1220 |

Regulatory documents contain more detailed tables that contain information not only about the cross section, but also about other geometric characteristics. They are the easiest way to determine the diameter of the pipes (in millimeters and inches). It is important to remember that by using special tables, you can calculate the necessary cross-section indicator (internal or external) both steel and other types of pipes.

### Finding the diameter of steel pipes: GOST table with thicknesses

The use of special tables located in the regulatory documentation allows you to quickly determine the required parameter. This can be an inner or outer diameter, and auxiliary geometric characteristics such as wall thickness, mass, etc. are also indicated.

It is worth noting that the difference between the outer diameter of the metal pipes and the Du can reach 7 mm (depending on the type of rolled metal). For example, electric-welded steel parts used in the installation of utility communications may differ in these indicators by 5-10 mm.

Table 3. Diameters and thickness of electric welded steel pipes:

Inner diameter (Dy), mm | Outer diameter, (Dn) mm | Wall thickness, mm |

80 | 89 | 3 |

15 | 20-22 | 1,5 |

50 | 57 | 3 |

100 | 108 | 3,5 |

32 | 42 | 2 |

20 | 25-28 | 1,5-2 |

40 | 48 | 3 |

25 | 30-32 | 2 |

The main indicator indicating the ownership of the product, of course, is the inner diameter. Pipes are also indicated by the external cross-section value, which is a necessary condition for calculating mechanical resistance.

Pay attention! The dimensions of products with inch markings are most easily determined by the tabular method. It is important to remember that when connecting lines made of steel with pipelines made of other material (for example, plastic), it is necessary to take into account not only Dy, but also Dn.

The popularity of the tabular method is due to the fact that combined pipeline structures are common in the modern world. Such systems contain steel pipes and polymer elements (fittings).

## Table of steel pipes: diameters, price per meter of rolled products

The cost of one meter of these products is determined by their weight. In this case, there is a certain dependence: the thicker the steel product, the greater its weight. On the Internet, you can find many tables that contain information about the prices of various parts classified by internal diameter. Steel pipes belong to the middle price segment. They are more expensive than polymer ones, but they are superior in strength and resistance to pressure.

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

Table 4. The cost of the most popular water and gas pipes made of steel:

Dy, mm | Price, rub. (per 1 m) |

50 | 80-170 |

15 | 32-70 |

40 | 80-108 |

32 | 53-95 |

20 | 40-50 |

Thus, the diameter of water pipes and gas transportation products has an impact on their cost. Parts that have a cross-section of more than 100 mm are practically not used in everyday life. The cost of such pipes is quite high, since 1 m of the part can weigh more than 10 kg. The heaviest pipe has a diameter of 1220 mm and a wall thickness of 16 mm. The weight of a meter of such a part is approximately 475 kg.

Diameter is a necessary characteristic, without which it is impossible to lay a pipeline structure. When determining this parameter, it is necessary to clearly understand that there are several varieties of it. In the tables that can be found in the relevant regulatory documentation, the inner diameter of steel products is most often indicated. If you decide to use a special formula to determine the cross section, it is recommended to pay attention to the examples containing the solution.