Fitting standards and certifications

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.

Who decides on standards and specifications for butt weld fittings ?

Manufacturers of butt weld pipe fittings have to meet specifications and requirements of many organizations, to assure quality, compatibility and performance of their products.

Key national and international standards organizations focus on materials and end-user industries, including American Society for Testing and Materials (ASTM), American Society of Mechanical Engineers (ASME), International Organization for Standardization (ISO), Norway’s NORSOK, …

Some international organizations also focus on quality standards across all industries, such as International Organization for Standardization (ISO).
Large industrial end-users also have their own programs to certify individual manufacturing plants as meeting their criteria to be listed on their Approved Manufacturers List (AML).

All these certifications and approvals are valid for a specific period, and must be renewed regularly.

Types of pipe fitting standards:

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:

ASTM International: American Society for Testing and Materials

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 volumes.

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:

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:

Hose Size In Nominal ID Inch Dash Size Standard Dash Size
1/4 3/16 -04
3/8 5/16 -06
1/2 13/32 -08
3/4 5/8 -12
1 7/8 -16
1 ½ - -
1 ¼ 1 1/8 -20

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 follows:

“ISO[/IEC] [IS] nnnnn[:yyyy] Title" where

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.

What is an MTR ?

Material Test Reports (MTRs) are provided by manufacturers to certify physical properties and metal grade or alloy for each fitting, flange, pipe, or valve. This MTR is essential for demanding applications (pressure, temperature, corrosion, abrasion,…)

Common type of Butt weld pipe fittings

A common example using welded pipe fitting is a pipe reduced by concentric reducer, welded to a weld neck flange and connected to an equipment. Figure below represent complete collection of butt welded pipe fitting



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