pipe dia

NB stands for "nomial bore". It is a first approximation to the inside diameter of the pipe. For example: a 40nb pipe has a nominal bore of 40mm or 1¹/₂in. The figure enables a first stab to be made at the friction losses in the pipe and to determine whether or not it is correctly sized.

Once the pipe has been sized, at a later date during the mechanical design the figure can be used to guide the piping designer into pipe system component selection, chiefly through look-up tables.

<...nomial bore...>

Typo: that should read "nominal bore". _{(Laptop running on low battery today...)}

Nominal bore is nothing but the inside diameter, but not exact.I think it is better to refer the machinery's hanbook.

Its Nominal Bore. Its is close to ID for pipe sizes below 12" and close to OD for pipe sizes equal or greater than 12". for exact dimentions of pipe (OD is fixed, as ID changes with Sch No. for a given size) refer standard pipe sizes in table ... either standard or suppliers catalogue.

Hi Mr.Madhavan

NB is Nominal Bore,

For Pipes please understand the following parameters first

1)NB is neither the outside diameter, nor inside diameter or average diameter for pipe sizes up to 12". For eg. 4" NB pipe is having OD equal to 4.5" . For pipe sizes 14" and above NB is same as Outer Diameter,This is ANSI standard.

2)Pipes are manufactured in standard sizes designated as NB

3)Outer diameter (OD) for a particular size pipe remains constant and inside diameter varies as the pipe thickness varies. Eg. 100 mm pipe (4" NB) is having a constant OD -4.5" ie; 114.3 mm approximate.( ID=OD - 2 times thk). This is the standard and you can get the OD for any pipe size from ANSI Pipe schedule chart.

4)For pipe size above 12", say 14" you can convert NB into mm by multiplying OD by 25.4 ie; OD in mm = 14NB * 25.4 = 355.6 mm (Inch to mm conversion 1"=25.4mm)

Hope the above is in order

Regards

Srijit

Pipe sizes are documented by a number of international standards, including API 5L, ANSI/ASME B36.10M and B36.19M in the US, BS 1600 and BS EN 10255 in the United Kingdom and Europe, and ISO 65 internationally.

There are two common methods for designating pipe outside diameter (OD). The North American method is called NPS ("Nominal Pipe Size") and is based on inches. The European version is called DN ("Diametre Nominel") and is based on millimetres. Designating the outside diameter allows pipes of the same size to be fit together no matter what the wall thickness.

• For pipe sizes less than NPS 14 inch (DN 350), both methods give a nominal value for the OD that is rounded off and is not the same as the actual OD. For example, NPS 2 inch and DN 50 are the same pipe, but the actual OD is 2.375 inch, or 60.325 mm. The only way to obtain the actual OD is to look it up in a reference table.

• For pipe sizes of NPS 14 inch (DN 350) and greater the NPS size is the actual diameter in inches and the DN size is equal to NPS times 25 rounded to a convenient multiple of 50. For example, NPS 14 has an OD of 14 inches, or 366.5 mm, and is equivalent to DN 350.

Since the outside diameter is fixed for a given pipe size, the inside diameter will vary depending on the wall thickness of the pipe. For example, 2" Schedule 80 pipe has thicker walls and therefore a smaller inside diameter than 2" Schedule 40 pipe.

Reference: http://en.wikipedia.org/wiki/Pipe_%28material%29#Sizes

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i guess like what the rest had said above, i dont think there is a NB to mm conversion. you have to refer to charts for that (since it's a std, grabbing any pipe catalogue with the given dimensions can be helpful)

and take note that for every designated NB the pipe comes in various thickness, so the OD(outer diameter) will be different.

Dear Aisling,

The OD for a given puipe size remains unchanged. The ID changes with the Sch. No.

Example:

1" Sch 10S pipe - OD 33.4 mm, thk- 2.77 mm so ID= OD-2*thk

1" Sch 40S pipe- OD- 33.4 mm, thk- 3.38 mm so ID= OD-2*thk

hope this clears your doubt.

yikes sorry, thanks; got it mixed up.