[Source: From web]

Steel pipe sizes

Nominal” refers to pipe in non-specific terms and identifies the diameter of the hole with a non-dimensional number (for example – 2-inch nominal steel pipe” consists of many varieties of steel pipe with the only criterion being a 2.375-inch (60.3 mm) outside diameter). Specific pipe is identified by pipe diameter and another non-dimensional number for wall thickness referred to as the Schedule (Sched. or Sch., for example – “2-inch diameter pipe, Schedule 40”).  Pipe size is quoted as a “Nominal Pipe Size” or NPS. The origin of the NPS numbers for smaller pipes (< NPS 12) is different to the origin for larger diameter pipes. However, all pipes of a specific NPS number have the same external or outer diameter (OD). The internal diameter will vary depending on the wall thickness of the metal. The reason for this is so that the same structural supports can be used for all piping of a specific NPS number regardless of the wall thickness.

Schedules

Steel pipe schedules are a way to describe the wall thickness of the pipe. This is a critical parameter as it is directly related to the strength of the pipe and the suitability for specific applications. A pipe schedule is a dimensionless number and is calculated based on the design formula for wall thickness, given the design pressure and allowable stress.

Examples of schedule numbers are as follows: 5, 5S, 10, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160, STD, XS, and XXS—with the most common being schedules 40 and 80. As the schedule number increases, the wall thickness of the pipe increases. The schedule number of a pipe therefore defines the internal diameter, as the OD is fixed by the NPS number.

The schedule number is roughly calculated as: Schedule = 1000 x (P/S) where P is the internal service pressure of the pipe (psig) and S is the ultimate tensile strength of the pipe material (psi).

SCHEDULE = 1000(P/S)

P = internal service pressure of pipe (psig)

S = ultimate stress of pipe material (psi)

Piping Materials

Pipe Material

Pipe Material

Piping material selection mainly depends on process conditions such as

  • Fluid it transports
  • at what temperature
  • at what pressure it transports
  • Cost of material
  • Availability – whether the material is locally available or import is required.
  • Weldability and Manufacturability of material also play a vital role in selection. Preference is always given to the material which does not require any special requirement during welding and manufacturing.

Material Characteristics

  • density
  • melting point
  • thermal conductivity
  • electrical conductivity (resistivity)
  • thermal expansion
  • corrosion resistance
  • Ultimate Tensile Strength – that is the capacity of a material to withstand when subjected to tension.
  • Yield Strength – that is the load at which plastic deformation or you can say permanent deformation start.
  • Elasticity – is the ability of a material to resume its normal shape after the load is removed just like rubber.
  • % Elongation – Percent elongation is a measure of ductility.
  • Hardness – is ability of a material to resist plastic deformation.
  • Toughness – ability of a material to absorb energy before fracture.
  • Creep resistance – ability to resist any kind of distortion when under a load over an extended period.
  • Fatigue Resistance – is ability of material to withstand cyclic load for a given number of cycles before it fails.

Frequently Used ASTM Grades for Various Piping Materials

Material Pipes Fttg Flg Valves Bolts and Nuts
Carbon Steel A106 Gr A A234 Gr WPA A105 A216 Gr WCB A193 Gr B7
A194 Gr 2H
A106 Gr B A234 Gr WPB A105 A216 Gr WCB
A106 Gr C A234 Gr WPC A105 A216 Gr WCB
Carbon Steel
Alloy
High-Temp
A335 Gr P1 A234 Gr WP1 A182 Gr F1 A217 Gr WC1 A193 Gr B7
A194 Gr 2H
A335 Gr P11 A234 Gr WP11 A182 Gr F11 A217 Gr WC6
A335 Gr P12 A234 Gr WP12 A182 Gr F12 A217 Gr WC6
A335 Gr P22 A234 Gr WP22 A182 Gr F22 A217 Gr WC9
A335 Gr P5 A234 Gr WP5 A182 Gr F5 A217 Gr C5
A335 Gr P9 A234 Gr WP9 A182 Gr F9 A217 Gr C12
Carbon Steel
Alloy
Low-Temp
A333 Gr 6 A420 Gr WPL6 A350 Gr LF2 A352 Gr LCB A320 Gr L7
A194 Gr 7
A333 Gr 3 A420 Gr WPL3 A350 Gr LF3 A352 Gr LC3
Austenitic
Stainless
Steel
A312 Gr TP304 A403 Gr WP304 A182 Gr F304 A182 Gr F304 A193 Gr B8
A194 Gr 8
A312 Gr TP316 A403 Gr WP316 A182 Gr F316 A182 Gr F316
A312 Gr TP321 A403 Gr WP321 A182 Gr F321 A182 Gr F321
A312 Gr TP347 A403 Gr WP347 A182 Gr F347 A182 Gr F347
Material Pipes Fttg Flg Valves Bolts and Nuts

ASTM Materials

Pipes

• A106 = This specification covers carbon steel pipe for high-temperature service.
• A335 = This specification covers seamless ferritic alloy-steel pipe for high-temperature service.
• A333 = This specification covers wall seamless and welded carbon and alloy steel pipe intended for use at low temperatures.
• A312 = Standard specification for seamless, straight-seam welded, and cold worked welded austenitic stainless steel pipe intended for high-temperature and general corrosive service.

Fittings

• A234 = This specification covers wrought carbon steel and alloy steel fittings of seamless and welded construction.
• A420 = Standard specification for piping fittings of wrought carbon steel and alloy steel for low-temperature service.
• A403 = Standard specification for wrought austenitic stainless steel piping fittings.

Flanges

• A105 = This specification covers standards for forged carbon steel piping components, that is, flanges, fittings, Valves, and similar parts, for use in pressure systems at ambient and higher-temperature service conditions.
• A182 = This specification covers forged or rolled alloy and stainless steel pipe flanges, forged fittings, and Valves and parts for high-temperature service.
• A350 = This specification covers several grades of carbon and low alloy steel forged or ring-rolled flanges, forged fittings and Valves for low-temperature service.

Valves

• A216 = This specification covers carbon steel castings for Valves, flanges, fittings, or other pressure-containing parts for high-temperature service and of quality suitable for assembly with other castings or wrought-steel parts by fusion welding.
• A217 = This specification covers steel castings, martensitic stainless steel and alloys steel castings for Valves, flanges, fittings, and other pressure-containing parts intended primarily for high-temperature and corrosive service.
• A352 = This specification covers steel castings for Valves, flanges, fittings, and other pressure-containing parts intended primarily for low-temperature service.
• A182 = This specification covers forged or rolled alloy and stainless steel pipe flanges, forged fittings, and Valves and parts for high-temperature service.

Bolts and Nuts

• A193 = This specification covers alloy and stainless steel bolting material for pressure vessels, Valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications.
• A320 = Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for Low-Temperature Service.
• A194 = Standard specification for nuts in many different material types.

What is Pipe NB (Nominal Bore)?

NPS is frequently referred as an NB (Nominal Bore). As such, there is no difference between NB and NPS. NB is also an American way to refer pipe dimensions.

What is DN (Diameter Nominal) Pipe Sizes?

DN or Diameter Nominal is International designation (SI or Matric Designator) and also a European equivalent of NPS to show pipe sizes. Here, you have to note that DN shows pipe sizes differently than NPS. For example, 2” pipe is simply mentioned as DN 50. You can get any NPS to DN by multiplying it with 25.

Standard Pipe Sizes and Dimensions

A Table of the Most Common Standard Pipe Sizes

Nominal Bore 1/2 inch (DN 15 mm), Outside Diameter 21.34 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.160 XXS
Wall Thickness (mm) 1.65 2.11 2.77 3.73 4.78 7.47
Internal Diameter (mm) 18.04 17.12 15.8 13.9 11.78 6.4
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 3/4 inch (DN 20 mm), Outside Diameter 26.67 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.160 XXS
Wall Thickness (mm) 1.65 2.11 2.87 3.91 5.56 7.82
Internal Diameter (mm) 23.37 22.45 20.93 18.85 15.55 11.03
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 1 inch (DN 25 mm), Outside Diameter 33.40 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.160 XXS
Wall Thickness (mm) 1.65 2.77 3.38 4.55 6.35 9.09
Internal Diameter (mm) 30.1 27.86 26.64 24.3 20.7 15.22
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 1.5 inch (DN 40 mm), Outside Diameter 48.3 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.160 XXS
Wall Thickness (mm) 1.7 2.8 3.7 5.1 7.1 10.2
Internal Diameter (mm) 45 42.7 40.9 38.1 34 27.9
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 2 inch (DN 50 mm), Outside Diameter 60.3 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.160 XXS
Wall Thickness (mm) 1.7 2.8 3.9 5.5 8.7 11.1
Internal Diameter (mm) 56.9 54.7 52.5 49.3 42.9 38.1
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 3 inch (DN 80 mm), Outside Diameter 88.9 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.160 XXS
Wall Thickness (mm) 2.1 3 5.5 7.6 11.1 15.2
Internal Diameter (mm) 84.7 82.9 77.9 73.7 66.7 58.5
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 4 inch (DN 100 mm), Outside Diameter 114.3 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.120 Sch.160 XXS
Wall Thickness (mm) 2.1 3 6 8.6 11.1 13.4 17.1
Internal Diameter (mm) 110.1 108.3 102.3 97.1 92.1 87.5 80.1
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 5 inch (DN 125 mm), Outside Diameter 141.3 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.120 Sch.160 XXS
Wall Thickness (mm) 2.8 3.4 6.6 9.5 12.7 15.9 19
Internal Diameter (mm) 135.7 134.5 128.1 122.3 115.9 109.5 103.2
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 6 inch (DN 150 mm), Outside Diameter 168.3 mm
Schedule Sch. 5 Sch. 10 STD XS Sch.120 Sch.160 XXS
Wall Thickness (mm) 2.8 3.4 7.1 11 14.3 18.3 22
Internal Diameter (mm) 162.7 161.5 154.1 146.3 139.7 131.7 124.3
Schedule 40 has same dimensions as STD. Schedule 80 has same dimensions as XS.
Nominal Bore 8 inch (DN 200 mm), Outside Diameter 219.1 mm
Schedule Sch. 5 Sch. 10 Sch. 20 Sch. 30 Sch. 40 Sch. 60 Sch. 80 Sch. 100 Sch. 120 Sch. 140 Sch. 160 XXS
Wall Thickness (mm) 2.8 3.8 6.4 7 8.2 10.3 12.7 15.1 18.2 20.6 23 22.2
Internal Diameter (mm) 213.5 211.5 206.3 205.1 202.7 198.5 193.7 188.9 182.7 177.9 173.1 174.7
Nominal Bore 10 inch (DN 250 mm), Outside Diameter 273.0 mm
Schedule Sch. 5 Sch. 10 Sch. 20 Sch. 30 Sch. 40 Sch. 60 Sch. 80 Sch. 100 Sch. 120 Sch. 140 Sch. 160 XXS
Wall Thickness (mm) 3.4 4.2 6.4 7.8 9.3 12.7 15.1 18.2 21.4 25.4 28.6 25.4
Internal Diameter (mm) 266.2 264.6 260.2 257.4 254.4 247.6 242.8 236.6 230.2 222.2 215.8 222.3
Nominal Bore 12 inch (DN 300 mm), Outside Diameter 323.9 mm
Schedule Sch. 5 Sch. 5 Sch. 10 Sch. 20 Sch. 30 Sch. 40 Sch. 40 Sch. 60 Sch. 80 Sch. 100 Sch. 120 Sch. 140 Sch. 160
Wall Thickness (mm) 4 4.2 4.6 6.4 8.4 9.5 10.3 14.3 17.5 21.4 25.4 28.6 33.3
Internal Diameter (mm) 315.9 315.5 314.7 311.1 307.1 304.9 303.3 295.3 228.9 281.1 273.1 266.7 257.3
Nominal Bore 14 inch (DN 350 mm), Outside Diameter 355.6 mm
Schedule Sch. 5 Sch. 10 Sch. 10 Sch. 20 Sch. 30 Sch. 40 XS Sch. 60 Sch. 80 Sch. 100 Sch. 120 Sch. 140 Sch. 160
Wall Thickness (mm) 4 4.8 6.4 7.9 9.5 11.1 12.7 15.1 19.1 23.8 27.8 31.8 35.7
Internal Diameter (mm) 347.7 346 342.9 339.8 336.6 333.3 330.2 325.4 317.5 308 300 292.1 284.2
STD has same dimensions as Schedule 30.
Nominal Bore 16 inch (DN 400 mm), Outside Diameter 406.4 mm
Schedule Sch. 5 Sch. 10 Sch. 10 Sch. 20 Sch. 30 Sch. 40 Sch. 60 Sch. 80 Sch. 100 Sch. 120 Sch. 140 Sch. 160
Wall Thickness (mm) 4.2 4.8 6.4 7.9 9.5 12.7 16.6 21.4 26.2 31 36.5 40.5
Internal Diameter (mm) 398 396.8 393.7 390.6 387.4 381 373.1 363.5 354 344.5 333.4 325.4
STD has same dimensions as Schedule 30. XS has the same dimensions as Schedule 40.

Note: You can easily convert inch dimension to mm by multiplying it with 25.4 and rounding as follows:-

  1. Outside diameter above 16 inches rounded to nearest 1 mm
  2. Outside diameter 16 inches and below rounded to nearest 0.1 mm
  3. Pipe wall thickness are rounded to nearest 0.01 mm

Dimension Tolerance for Carbon Steel and Stainless Steel Pipe Sizes and Schedule As per ASTM A530/A530M-12 and ASTM A999/A999M-15

Common dimension tolerances are listed in ASTM A530. However, each product has its own requirements and when given in that specification that will govern over the A530.

 Description Size Over Under
Weight NPS 12 (DN 300) and under 10% 3.50%
Weight NPS 14 (DN 350) and above (Note-1) 10% 5%
Wall Thickness
Seamless and Welded Pipe 1⁄8 to 2 ½, incl., all t/D ratios (Note-2) 20.00% 12.50%
3 to 18 incl., t/D up to 5 % incl. 22.50% 12.50%
3 to 18 incl., t/D > 5 % 15.00% 12.50%
20 and larger, welded, all t/D ratios (Note-3) 17.50% 12.50%
20 and larger, seamless, t/D up to 5 % incl. 22.50% 12.50%
20 and larger, seamless, t/D > 5 % 15.00% 12.50%
Forged and Bored Pipe 1/8 in.(3.2mm) Nil
Cast Pipe 1/6 in.(1.6mm) Nil
Inside Diameter for Cast Pipe Nil 1⁄16 in. (1.6 mm)
Outside Diameter (Note-4)
Diameter Outside 1⁄8 to 11⁄2, incl 1⁄64 in. (0.4mm) 1/32 in.  (0.8mm)
Over 1 ½ to 4, incl 1/32 in.  (0.8mm) 1/32 in.  (0.8mm)
Over 4 to 8, inc 1/16 in. (1.6mm) 1/32 in. (0.8mm)
Over 8 to 18, incl 3/32 in. (2.4mm) 1/32 in. (0.8mm)
Over 18 to 26, incl 1/8 in.  (3.2mm) 1/32 in. (0.8mm)
Over 26 to 34, incl 5/32 in. (4.0mm) 1/32 in. (0.8mm)
Over 34 3/8 in. (4.8mm) 1/32 in. (0.8mm)
  • Note-1: Pipe of NPS 4 (DN 100) and smaller may be weighed in lots; pipe in sizes larger than NPS 4 (DN 100) shall be weighed separately.
  • Note-2: t = Nominal wall thickness. D = Outside diameter.
  • Note-3: For welded pipe, the weld area shall not be limited by the over tolerance.
  • Note-4: For thin-wall pipe, the ovality in any one cross-section shall not exceed 1.5 % of the specified outside diameter.

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