Seamless steel pipe and the meaning of the standards

Seamless steel pipe and the meaning of the standards

On each type of steel pipe, there will be technical standards and symbols, with Tiger Steel learn the parameters and symbols as follows.

DN: is the nominal diameter.


For example DN15 or 15A, equivalent to pipe of nominal outside diameter
However, pipes manufactured to different standards will have different actual external diameters

ống thép đúc


Many people often mistakenly think that the DN15 tube is a 15mm non-tube. When we have the actual outside diameter, we only need to subtract 2 from the outer diameter
Inner diameter (mm) = Outer diameter (mm) 2x thickness (mm)

* Phi: nominal outside diameter.

­ In Vietnam, the most familiar unit for measuring pipe diameter is still phi (Ø), ie mm (shown above, for each production standard, the pipe will also have outside diameters. Both manufacturers publish their own production standards, and for each type of pipe.

* Inch (“):


A commonly used unit is the Inch (abbreviated symbol).
Many people will be confused in the conversion from Inch to DN or phi
This easy to confuse, perhaps will be overcome by the conversion table, and specific parameters
Table of nominal pipe sizes
This table corresponds to some standards such as: ASTM A106, A53, API 5L, A312, ASME …
Pipe from ⅛ ”to 3½” (from DN6 – DN90)

quy cách ống thép đúc tiêu chuẩn astm

InchDNOuter diameter (mm)Pipe wall thickness
610,29 mm0,889 mm1,245 mm1,448 mm1,727 mm
¼813,72 mm1,245 mm1,651 mm1,854 mm2,235 mm
1017,15 mm1,245 mm1,651 mm1,854 mm2,311 mm
½1521,34 mm1,651 mm2,108 mm2,769 mm
¾2026,67 mm1,651 mm2,108 mm2,870 mm
12533,40 mm1,651 mm2,769 mm3,378 mm
3242,16 mm1,651 mm2,769 mm2,972 mm3,556 mm
4048,26 mm1,651 mm2,769 mm3,175 mm3,683 mm
25060,33 mm1,651 mm2,769 mm3,175 mm3,912 mm
6573,03 mm2,108 mm3,048 mm4,775 mm5,156 mm
38088,90 mm2,108 mm3,048 mm4,775 mm5,486 mm
90101,60 mm2,108 mm3,048 mm4,775 mm5,740 mm

Pipe from 4 ″ to 8 ″ (from DN100 – DN200)

 InchDNmmOuter diameter (mm)
4100114,30 mm2,108 mm3,048 mm4,775 mm
115127,00 mm
5125141,30 mm2,769 mm3,404 mm
6150168,28 mm2,769 mm3,404 mm
8200219,08 mm2,769 mm3,759 mm6,350 mm7,036 mm

Tube from 10 ″ to 24 ″ (from DN250 – DN600)

 InchDNmmOuter DK (mm)Pipe wall thickness (mm)
SCH 5sSCH 5SCH 10sSCH 10
10250273,05 mm3,404 mm3,404 mm4,191 mm4,191 mm
12300323,85 mm3,962 mm4,191 mm4,572 mm4,572 mm


14350355,60 mm3,962 mm3,962 mm4,775 mm6,350 mm
16400406,40 mm4,191 mm4,191 mm4,775 mm6,350 mm
18450457,20 mm4,191 mm4,191 mm4,775 mm6,350 mm
20500508,00 mm4,775 mm4,775 mm5,537 mm6,350 mm
24600609,60 mm5,537 mm5,537 mm6,350 mm6,350 mm
 InchPipe wall thickness (mm)
SCH 40sSCH 40SCH 60SCH 80sSCH 80SCH 100
109,271 mm9,271 mm12,700 mm12,700 mm15,062 mm18,237 mm
129,525 mm10,312 mm12,700 mm12,700 mm17,450 mm21,412 mm
149,525 mm11,100 mm15,062 mm12,700 mm19,050 mm23,800 mm
169,525 mm12,700 mm16,662 mm12,700 mm21,412 mm26,187 mm
189,525 mm14,275 mm19,050 mm12,700 mm23,800 mm29,362 mm
209,525 mm15,062 mm20,625 mm12,700 mm26,187 mm32,512 mm
249,525 mm17,450 mm24,587 mm12,700 mm30,937 mm38,887 mm


2,413 mm
3,023 mm
3,200 mm
3,734 mm7,468 mm
3,912 mm7,823 mm
4,547 mm9,093 mm
4,851 mm9,703 mm
5,080 mm10,160 mm
5,537 mm6,350 mm11,074 mm
7,010 mm7,620 mm14,021 mm
7,620 mm8,890 mm15,240 mm
8,077 mm16,154 mm


Pipe wall thickness (mm)
SCH 40STDSCH 60SCH 80SCH 100SCH 120SCH 140SCH 160
6,020 mm7,137 mm8,560 mm11,100 mm13,487 mm
6,274 mm9,017 mm
6,553 mm9,525 mm12,700 mm15,875 mm
7,112 mm10,973 mm14,275 mm18,263 mm
8,179 mm10,312 mm12,700 mm15,062 mm18,237 mm20,625 mm23,012 mm


SCH 20SCH 30
6,350 mm7,798 mm
6,350 mm8,382 mm


7,925 mm9,525 mm
7,925 mm9,525 mm
7,925 mm11,100 mm
9,525 mm12,700 mm
9,525 mm14,275 mm
SCH 120SCH 140SCH 160
21,412 mm25,400 mm28,575 mm
25,400 mm28,575 mm33,325 mm
27,762 mm31,750 mm35,712 mm
30,937 mm36,500 mm40,462 mm
34,925 mm39,675 mm45,237 mm
38,100 mm44,450 mm49,987 mm
46,025 mm52,375 mm59,512 mm

See more about Hoa Phat galvanized steel pipe

Hotline: 0767.555.777
Address: 551/156 Le Van Khuong, District 12

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