Analysis Of Steel Pipe Size System

Basic parameter system of steel pipe

The size unit of steel pipe is based on the nominal pipe diameter as a parameter to indicate the size of the outer diameter of the pipe. The standard NPS uses the imperial unit. The larger the outer diameter, the larger the value. In the public service system, it is expressed by the diameter nominal (DN). For example, DN100 corresponds to NPS 4, and 4 NPS corresponds to an outer diameter of 114.3 mm. There is a corresponding relationship between DN and NPS. Both are dimensionless units. The pipe specifications need to be defined in conjunction with the wall thickness parameter (Schedule).

Wall thickness and schedule (Schedule)

The higher the SCH value, the thicker the wall thickness. The thicker the wall thickness, the stronger the pressure resistance. SCH 40 is a common standard wall thickness. SCH 80 has a thicker wall thickness and is more suitable for high-pressure scenarios. Stainless steel pipes and carbon steel pipes all use the NPS system, but the actual wall thickness corresponding to SCH may be slightly different due to differences in material standards.

Carbon steel pipe wall thickness comparison (ANSI B36.10 standard)

Stainless steel pipe wall thickness comparison (ASME B36.19 standard)

Stainless steel pipe

Stainless steel is widely used in food, natural gas and oil fields. Its design and manufacturing follow ASME B36.19. Its SCH is synchronized with carbon steel pipe. Stainless steel is usually used in some harsh environments with strong corrosion, so the corrosion resistance of stainless steel should be specially considered in the wall thickness calculation formula
The stainless steel mark is 4 NPS SCH 40S, where S is used to indicate stainless steel material, which can better distinguish steel pipes of other materials.

Carbon Steel Pipe

Carbon steel pipe is widely used in various industries and is the most common pipeline material in the industrial field. It is mainly based on ANSI B36.10 standard.
Its SCH value directly indicates the wall thickness. For example, 4 NPS SCH 40″ means a carbon steel pipe with a nominal diameter of 4 inches and a wall thickness grade of 40, and its wall thickness is 6.02 mm.
Galvanized steel pipe is also a common type of carbon steel pipe. It is used in environments such as outdoor water supply that require anti-corrosion materials. The surface is galvanized to form a corrosion-resistant protective layer.

Metric and Imperial Conversion

In global projects, steel pipe sizes must take into account metric units: