Nominal Pipe Size
Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. The name NPS is based on the earlier “Iron Pipe Size” (IPS) system.
That IPS system was established to designate the pipe size. The size represented the approximate inside diameter of the pipe in inches. An IPS 6″ pipe is one whose inside diameter is approximately 6 inches. Users started to call the pipe as 2inch, 4inch, 6inch pipe and so on. To begin, each pipe size was produced to have one thickness, which later was termed as standard (STD) or standard weight (STD.WT.). The outside diameter of the pipe was standardized.
As the industrial requirements handling higher pressure fluids, pipes were manufactured with thicker walls, which has become known as an extra strong (XS) or extra heavy (XH). The higher pressure requirements increased further, with thicker wall pipes. Accordingly, pipes were made with double extra strong (XXS) or double extra heavy (XXH) walls, while the standardized outside diameters are unchanged. Note that on this website only terms XS and XXS are used.
Pipe Schedule
So, at the IPS time only three walltickness were in use. In March 1927, the American Standards Association surveyed industry and created a system that designated wall thicknesses based on smaller steps between sizes. The designation known as nominal pipe size replaced iron pipe size, and the term schedule (SCH) was invented to specify the nominal wall thickness of pipe. By adding schedule numbers to the IPS standards, today we know a range of wall thicknesses, namely.
SCHEDULE: 1,000( P/S)
P = internal service pressure of the pipe (psig)
S =ultimate tensile strength of the pipe material (psi).
SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS and XXS.
Nominal pipe size (NPS) is a dimensionless designator of pipe size. It indicates standard pipe size when followed by the specific size designation number without an inch symbol. For example, NPS 6 indicates a pipe whose outside diameter is 168.3 mm.
The NPS is very loosely related to the inside diameter in inches, and NPS 12 and smaller pipe has outside diameter greater than the size designator. For NPS 14 and larger, the NPS is equal to 14inch.
For a given NPS, the outside diameter stays constant and the wall thickness increases with larger schedule number. The inside diameter will depend upon the pipe wall thickness specified by the schedule number.
SUMMERY
Pipe size is specified with two non-dimensional numbers,
- nominal pipe size (NPS)
- schedule number (SCH)
and the relationship between these numbers determine the inside diameter of a pipe.
Stainless Steel Pipe dimensions determined by ASME B36.19 covering the outside diameter and the Schedule wall thickness. Note that stainless wall thicknesses to ASME B36.19 all have an “S” suffix. Sizes without an “S” suffix are to ASME B36.10 which is intended for carbon steel pipes.
The International Standards Organization (ISO) also employs a system with a dimensionless designator.
Diameter nominal (DN) is used in the metric unit system. It indicates standard pipe size when followed by the specific size designation number without a millimeter symbol. For example, DN 80 is the equivalent designation of NPS 3. Below a table with equivalents for NPS and DN pipe sizes.
|
4
|
3.1/2
|
3
|
2.1/2
|
2
|
1.1/2
|
1.1/4
|
1
|
3/4
|
1/2
|
NPS
|
|---|---|---|---|---|---|---|---|---|---|---|
|
100
|
90
|
80
|
65
|
50
|
40
|
32
|
25
|
20
|
15
|
DN
|
Note..
For NPS ≥ 4, the related DN = 25 multiplied by the NPS number
Do you now what is “ein zweihunderter Rohr”..Germans means with that a pipe NPS 8 or DN 200. In this case, the Dutch talking about a “8 duimer”. I’m really curious how people in other countries indicates a pipe.
Examples of actual O.D. and I.D.
Actual outside diameters
- 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)
Actual inside diameters of a 1 inch pipe.
- NPS 1-SCH 40 = O.D.33,4 mm – WT. 3,38 mm – I.D. 26,64 mm
- NPS 1-SCH 80 = O.D.33,4 mm – WT. 4,55 mm – I.D. 24,30 mm
- NPS 1-SCH 160 = O.D.33,4 mm – WT. 6,35 mm – I.D. 20,70 mm
Such as above defined, no inside diameter corresponds to the truth 1″ (25,4 mm).
The inside diameter is determined by the wall thickness (WT).
ASTM | Carbon Steel | Alloy Steel | Seamless | Welded | Usage to be used |
A53 | √ | √ | ERW/FBW | General | |
A106 | √ | √ | High temperature | ||
A179 | √ | √ | Exchanges | ||
A200 | √ | √ | Refinery | ||
A209 | √ | √ | Boiler | ||
A213 | √ | √ | Boiler | ||
A333 | √ | √ | √ | EFW without filler metal | Low temperature |
A335 | √ | √ | High Temperature | ||
A671 | √ | √ | EFW with filler metal | Atmospheric Lower Temperature | |
A672 | √ | √ | EFW with filler metal | Moderate Temperature | |
A691 | √ | √ | EFW with filler metal | High Temperature |
ASTM A 53 ( Carbon Steel )
This specification covers seamless and welded black and hot – dipped galvanized Steel pipe in NPS 1/8 to 26 inclusive with nominal wall thickness
ASTM A 106 (Carbon Steel)
This specification covers seamless carbon steel pipe for high temperature
ASTM A 179 / A179 M (Carbon Steel)
This specification coves seamless cold draw low carbon steel heat – exchanger and condenser tubes 1/8” (3.2mm) to 3” (76.2) included in outside diameter
ASTM A200 (alloy steels)
This specification covers several grades of minimum wall Thick ness chromium- molybdenum and chromium-molybdenum-silicon, -seamless hot finished and cold finished, intermediate alloy – steel tubes, for use in carrying fluids at elevated temperatures and pressure in various types of heaters, in which the tubes may be subjected to a furnace temperature higher Than that of that of the contained fluid size
Size range outside diameter: (50.8 to 228.6mm)
ASTM A 209 (alloy Steels)
This specification covers several grades of minimum wall Thick ness, seamless, carbon – molybdenum alloy Steel, boiler and super heater tube.
Size range: outside diameter 12.7 mm to 127mm
ASTM 213/ A213 ( ferritic alloy Steel )
This specification covers minimum- wall- thickness, seamless ferritic and austenitic Steel , boiler and super heater tubes
Size range ( 3.2mm) in inside diameter to ( 127mm) in outside diameter.
ASTM A333/ A 333m (Low temperature Steels)
This specification covers seamless and welded Steel pipe for low temperature service
ASTM A335/A335m (alloy Steel)
This specification covers the seamless ferritic alloy Steel pipes for high Temperature service
ASTM A671 / A672-94 /ASTM A691
This specification cover electric- fusion welded Steel pipe with filler metal added, fabricated form pressure vessel quality plate and Suitable for high pressure service
- A 671-94: at atmospheric and lower temperature.
- A 672-94: at moderate temperature
- A 691-93: at high temperature
Size range: outside diameter: 405 mm or larger
Wall Thickness: (604mm or greater)
ASME B 36.10
This standard covers the standardization of dimensions of welded and seamless wrought steel pipe for high or low temperatures and pressure.
Casing & Driil pipes
This standard is for carbon steel and alloy steel
Wall thickness is o.312 to 2 in ( 105 to 126 mm)
Standard: ASTM A 106 – 2006 , API 5 CT , API 5 L,API 5 DP, ASME /ANSI B 36.10
PSL 1 A25 – A-B – X 42 – X46- X52 – X56- X60 – X65 – X70
PSL 2 B – X 42 – X 46 – X 52 – X 56 – X 60 – X65 – x 70 – X80