| The
following information and table is derived from ISO 6708 and ASME B36.10M,
and from the update to the API SOME Standards Paragraphs in September
2004. The explanations of DN and NPS as presented here are not intended as definitions
to be copied into the Standards, they are simply explanations.
DN
alphanumeric designation of
size for components of a pipework system, which is used for reference
purposes. It comprises the letters DN followed by a dimensionless whole
number which is indirectly related to the physical size, in
millimeters, of the bore or outside diameter of the end
connection. However, the number following the letters DN does not represent a
measurable value and should not be used for calculation purposes except
where specified in the relevant standard.
NPS
Nominal Pipe Size in inches.
alphanumeric designation of
size for components of a pipework system, which is used for reference
purposes. It comprises the letters NPS followed by a
number or fraction (without an inch symbol) which is nominally related to the physical size, in
inches, of the bore (NPS 1/8 to NPS 12) or outside diameter (NPS 14 and
larger) of the pipe.
TABLE OF CORRESPONDENCE
The following
table lists the corresponding DN and NPS pipe sizes for use if referencing these two systems of pipe size
designations in the standards.
|
Diameter
Nominal
- DN -
(mm)
|
Nominal
Pipe Size
- NPS -
(inches)
|
|
6
|
1/8
|
|
8
|
¼
|
|
10
|
3/8
|
|
15
|
½
|
|
20
|
¾
|
|
25
|
1
|
|
32
|
1
¼
|
|
40
|
1
½
|
|
50
|
2
|
|
65
|
2
½
|
|
80
|
3
|
|
100
|
4
|
|
150
|
6
|
|
200
|
8
|
|
250
|
10
|
|
300
|
12
|
|
350
|
14
|
|
400
|
16
|
|
450
|
18
|
|
500
|
20
|
|
550
|
22
|
|
600
|
24
|
|
650
|
26
|
|
700
|
28
|
|
750
|
30
|
|
800
|
32
|
|
900
|
36
|
|
1000
|
40
|
|
1100
|
42
|
|
1200
|
48
|
|
1400
|
54
|
|
1500
|
60
|
|
1600
|
64
|
|
1800
|
72
|
|
2000
|
80
|
|
2200
|
88
|
In the United States, term "NPT" is
sometimes used:
NPT
National Pipe Thread - see ASME B1.20.1
It is designated by specifying in sequence the nominal pipe size, the
number of threads per inch and a "thread series symbol" (and for
left hand threads, this is followed by LH).
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