Stainless Steel Tube & Pipe Sizes: NPS, Pipe Schedule, DN

There are several common methods for describing pipe and tube dimension used in tubular piping system, we should calculate exact sizes without confusion, usually tube and pipe sizes is defined by outside diameter, wall thickness and length, inside diameter is also mentioned for tube sizes, these parameters are basic to dimensions concept.

Nominal Pipe Size

The North American ANSI system is widely applied in pipe system, Nominal Pipe Size (NPS澳门凯发娱乐) is defined standard sizes for pipes used for different pressures and temperatures, the outside diameter is used in inches, NPS and OD values are not always equal, from NPS ⅛ to 12 inch, the NPS and OD values are different, over 14 inch, the NPS and OD values are equal, the size is actual dimensions, not nominal.

NB

NB (Nominal Bore) is also another method to refer pipe sizes and dimensions, it is the same value between NB and NPS。

Pipe Schedule

Wall thickness referred to as the Schedule (Sch澳门凯发娱乐.), nowadays, there are large selection of wall thicknesses to meet all applications under different pressure, standard weight (STD), extra-strong (XS), and double extra-strong (XXS) is three main number for thickness, 5S and 10S are thinner wall thickness for stainless steel pipe.

DN Size

The European ISO system is also OD based, Diameter Nominal (DN) is also frequently referred to pipe dimensions, it provides almost the same OD as the ANSI system, but measured in millimeters, and with a lot more choices for different wall thickness。

Nominal Pipe Size, Diameter Nominal and pipe Schedule Chart

ASME B36.19 indicates Stainless Steel Pipe dimensions including the outside diameter and the Schedule wall thickness, the Schedule Number has an “S” suffix for wall thickness, having SCH 5S, SCH 10S, SCH 40S, SCH 80S.

ASME B36.10 standard determines carbon steel pipe dimensions, without an “S” suffix for pipe schedule.

Nominal Size OD Wall Thickness, SCH
NPS DN mm 5S 10S 10 20 30 40S STh 40 60 80S XS 80 100 120 140 160 XXS
1∕8 6 10.3 1.24 1.73 1.73 1.73 2.41 2.41 2.41
1∕4 8 13.7 1.65 2.24 2.24 2.24 3.02 3.02 3.02
3∕8 10 17.2 1.65 2.31 2.31 2.31 3.2 3.2 3.2
1∕2 15 21.3 1.65 2.11 2.77 2.77 2.77 3.73 3.73 3.73 4.78 7.47
3∕4 20 26.7 1.65 2.11 2.87 2.87 2.87 3.91 3.91 3.91 5.56 7.82
1 25 33.4 1.65 2.77 3.38 3.38 3.38 4.55 4.55 4.55 6.35 9.09
1 1∕4 32 42.2 1.65 2.77 3.56 3.56 3.56 4.85 4.85 4.85 6.35 9.7
1 1∕2 40 48.3 1.65 2.77 3.68 3.68 3.68 5.08 5.08 5.08 7.14 10.15
2 50 60.3 1.65 2.77 3.91 3.91 3.91 5.54 5.54 5.54 8.74 11.07
2 1∕2 65 73 2.11 3.05 5.16 5.16 5.16 7.01 7.01 7.01 9.53 14.02
3 80 88.9 2.11 3.05 5.49 5.49 5.49 7.62 7.62 7.62 11.13 15.24
3 1∕2 90 101.6 2.11 3.05 5.74 5.74 5.74 8.08 8.08 8.08
4 100 114.3 2.11 3.05 6.02 6.02 6.02 8.56 8.56 8.56 11.13 13.49 17.12
5 125 141.3 2.77 3.4 – – 6.55 6.55 6.55 9.53 9.53 9.53 12.7 15.88 19.05
6 150 168.3 2.77 3.4 7.11 7.11 7.11 10.97 10.97 10.97 14.27 18.26 21.95
8 200 219.1 2.77 3.76 6.35 7.04 8.18 8.18 8.18 10.31 12.7 12.7 12.7 15.09 18.26 20.62 23.01 22.23
10 250 273.1 3.4 4.19 6.35 7.8 9.27 9.27 9.27 12.7 12.7 12.7 15.09 18.26 21.44 25.4 28.58 25.4
12 300 323.9 3.96 4.57 6.35 8.38 9.53 9.53 10.31 14.27 12.7 12.7 17.48 21.44 25.4 28.58 33.32 25.4
14 350 355.6 3.96 4.78 6.35 7.92 9.53 9.53 11.13 15.09 12.7 19.05 23.83 27.79 31.75 35.71
16 400 406.4 4.19 4.78 6.35 7.92 9.53 9.53 12.7 16.66 12.7 21.44 26.19 30.96 36.53 40.49
18 450 457.2 4.19 4.78 6.35 7.92 11.13 9.53 14.27 19.05 12.7 23.83 29.36 34.93 39.67 45.24
20 500 508 4.78 5.54 6.35 9.53 12.7 9.53 15.09 20.62 12.7 26.19 32.54 38.1 44.45 50.01
22 550 558.8 4.78 5.54 6.35 9.53 12.7 9.53 22.23 12.7 28.58 34.93 41.28 47.63 53.98
24 600 609.6 5.54 6.35 6.35 9.53 14.27 9.53 17.48 24.61 12.7 30.96 38.89 46.02 52.37 59.54
26 650 660.4 7.92 12.7 9.53 12.7
28 700 711.2 7.92 12.7 15.88 9.53 12.7
30 750 762 6.35 7.92 7.92 12.7 15.88 9.53 12.7
32 800 812.8 7.92 12.7 15.88 17.48 9.53 17.48 12.7
34 850 863.6 7.92 12.7 15.88 17.48 9.53 17.48 12.7
36 900 914.4 7.92 12.7 15.88 19.05 9.53 19.05 12.7
38 950 965.2 9.53 12.7
40 1000 1016 9.53

SUMMARY: from above table, we can see that:

  • NPS and DN value are different, they have a corresponding value for outside diameter in millimeter, when NPS ≥ 4, the related DN = 25 multiplied by the NPS number.
  • From NPS 1/8 to NPS 12 (including) the value is nominal, not actual OD, for example, NPS 6 inch (DN150), pipe outside diameter should be 168.3 mm, not 152.4 mm.
  • When NPS over and including 14, pipe OD should actual dimension, for example, NPS20 inch, the diameter should be 508 mm, it convert inch to mm by multiplying it with 25.4.
  • Pipe inside diameter is defined by outside diameter and Schedule.

Examples Of actual outside diameter

  • NPS 1 actual O.D. = 1.5/16″ (33.4 mm)
  • NPS 2 actual O.D. = 2.3/8″ (60.3 mm)
  • NPS 3 actual O.D. = 3.1/2″ (88.9 mm)
  • NPS 4 actual O.D. = 4.1/2″ (114.3 mm)
  • NPS 12 actual O.D. = 12.3/4″ (323.9 mm)
  • NPS 14 ACTUAL O.D. = 14″(355.6 MM, 14 x 25.4 mm)

Difference Between Pipe And Tube Dimension

In general, NPS is a pipe sizes number which refers to a nominal diamter, not actual diamter as specified above, the actual physical OD is larger than it’s nominal OD, and schedule number is for pipe thickness mentioned, pipe can be measured by inside diameter, because pipe is used to transportation fluid, it needs to calculate relevant parameter。

Tube sizes is expressed in inch or millimeter, it is actual value, the actual physical OD of a tube is just the same as it’s nominal OD in both outside diameter and wall thickness, tube dimension in wall thickness is not expressed by Schedule Numble, see more tube size chart.

tube pipe difference

Reading more about pipe and tube differences.

BWG

BWG stands for “Birmingham Wire Gauge”,  each BWG number represents a specific steel tubing thickness, BWG number decreases with increasing thickness of the tube, for example, BWG16, the wall thickness is 1.65 mm.

BWG, SWG and ASWG can be converted in inch and mm.

Shapes and Sizes

We usually mention tube and pipe size is round shape, in fact, other shapes of tube and pipe have special sizes to specify, generally use in structure and decorative purpose, these shapes include:

Dimension Tolerance

When measure tube and pipe sizes, the tolerance is required strictly as standard, which specified dimensions Permissible Variations, including outside diameter tolerance, wall thickness tolerance, length tolerance, straightness and ovality, more details in 澳门凯发娱乐Tube & Pipe Tolerances.