Pipe Fitting Standards
With the rapid expansion in the global trade, standardization of various products has become an essential requirement. The standards given to various products significantly contributes towards increasing international trade which in turn bridges the quality gap between the manufacturers, producers and buyers of different nations. In pipe fittings as well, standards play a vital role. The manufacture and installation of pipe fittings is tightly regulated by various standards and codes.
The integrity of pipe fittings and flanges in the piping system depends on various principles used in design, construction and maintenance of the entire system. The components of pipe fittings are made in different materials, in a variety of types and sizes and hence should be manufactured according to common national standards or according to manufacturers' proprietary item. Some manufacturers also use their own internal piping standards based upon national and industry sector standards.
Difference between “Standard” and “Codes”:
Piping codes imply the requirements of design, fabrication, use of materials, tests and inspection of various pipe and piping system. It has a limited jurisdiction defined by the code. On the other hand, piping standards imply application design and construction rules and requirements for pipe fittings like adapters, flanges, sleeves, elbows, union, tees, valves etc. Like a code, it also has a limited scope defined by the standard.
Factors affecting standards:
“Standards” on pipe fittings are based on certain factors
like as follows:
Types of pipe fitting standards:
- Pressure-temperature ratings
- End connections
- Dimensions and tolerances
- Pattern taper etc.
Some widely used pipe fitting standards are as follows:
- ANSI: The American National Standards Institute
ANSI is a private, non-profit organization. Its main function is to
administer and coordinate the U.S. voluntary standardization and
conformity assessment system. It provides a forum for development of
American national standards. ANSI assigns "schedule numbers".
These numbers classify wall thicknesses for different pressure uses.
- ASME: American Society for Mechanical Engineers
This is one of the reputed organizations in the world developing
codes and standards. The schedule number for pipe fitting starts
from ASME/ANSI B16. The various classifications of ASME/ANSI B16
standards for different pipe fittings are as follows:
- ASME/ANSI B16.1 - 1998 - Cast Iron Pipe Flanges and Flanged
- ASME/ANSI B16.3 - 1998 - Malleable Iron Threaded Fittings
- ASME/ANSI B16.4 - 1998 - Cast Iron Threaded Fittings
- ASME/ANSI B16.5 - 1996 - Pipe Flanges and Flanged Fittings
- ASME/ANSI B16.11 - 2001 - Forged Steel Fittings,
Socket-Welding and Threaded
- ASME/ANSI B16.14 - 1991 - Ferrous Pipe Plugs, Bushings and
Locknuts with Pipe Threads
- ASME/ANSI B16.15 - 1985 (R1994) - Cast Bronze Threaded
- ASME/ANSI B16.25 - 1997 - Buttwelding Ends
- ASME/ANSI B16.36 - 1996 - Orifice Flanges etc.
- ASTM International: American Society for Testing and
This is one of the largest voluntary standards development
organizations in the world. It was originally known as the American
Society for Testing and Materials (ASTM). This is a reputed
scientific and technical organization that develops and publishes
voluntary standards on the basis of materials, products, systems and
services. This is a trusted name for standards. The standards
covered by this organization covers various types of pipes, tubes
and fittings, especially made of metal, for high-temperature
service, ordinary use and special applications like fire protection.
The ASTM standards are published in 16 sections consisting of 67
- AN: Here, "A" stands for Army and "N"
stands for Navy
The AN standard was originally designed for the U.S. Military.
Whenever, a pipe fitting is AN fittings, it means that the fittings
are measured on the outside diameter of the fittings, that is, in
1/16 inch increments. For example, an AN 4 fitting means a fitting
with an external diameter of approximately 4/16" or ¼".
It is to be noted that approximation is important because AN
external diameter is not a direct fit with an equivalent NPT thread.
- BSP: British Standard Pipe
BSP is the U.K. standard for pipe fittings. This refers to a family
of standard screw thread types for interconnecting and sealing pipe
ends by mating an external (male) with an internal (female) thread.
This has been adopted internationally. It is also known as British
Standard Pipe Taper threads (BSPT )or British Standard Pipe Parallel
(Straight) threads (BSPP ). While the BSPT achieves pressure tight
joints by the threads alone, the BSPP requires a sealing ring.
- DIN: Deutsches Institut für Normung
This refers to the industrial pipe, tube and fittings standards and
specifications from the DIN, Deutsches Institut für Normung
which in English means the German Institute for Standardization. DIN
is the German national organization for standardization and is ISO
member body for that country.
DIN standard designation
The designation of a DIN standard shows its origin where #
symbolizes a number:
- DIN # : Used for German standards having mainly
domestic significance or designed as the primary step toward
- DIN EN # : Used for the German edition of European
- DIN ISO # : Used for the German edition of ISO
- DIN EN ISO # : Used if the standard has also been
adopted as a European standard.
- Dash (-) size
Dash size is the standard used to refer to the inside diameter of a
hose. This indicates the size by a two digit number which represents
the relative ID in sixteenths of an inch. This is also used
interchangeably with AN fittings. For example, a Dash "8"
fitting means an AN 8 fitting. A standard hose guide is given below:
Flanges: Ratings in Classes and Pressure Numbers (PN)
ID Inch Dash Size
Flange Pressure Number, PN
ISO: International Organization for Standardization
ISO is the industrial pipe, tube and fittings standards and
specifications from the International Organization for
Standardization. ISO standards are numbered. They have format as
“ISO[/IEC] [IS] nnnnn[:yyyy] Title" where
nnnnn: standard number
yyyy: year published, and
Title: describes the subject
JIS: Japanese Industrial Standards
This is the Japanese industrial standards or the standards used for
industrial activities in Japan for pipe, tube and fittings and
published through Japanese Standards Associations.
NPT: National Pipe Thread
National Pipe Thread is a U.S. standard straight (NPS) threads or
for tapered (NPT) threads. This is the most popular US standard for
pipe fittings. NPT fittings are based on the internal diameter (ID)
of the pipe fitting.
The points mentioned below will be a guide for the buyers: