General standard & certifications of fittings

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:

  • ASME/ANSI B16.1 – 1998 – Cast Iron Pipe Flanges and Flanged Fittings
  • 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 Fittings
  • ASME/ANSI B16.25 – 1997 – Buttwelding Ends
  • ASME/ANSI B16.36 – 1996 – Orifice Flanges etc.

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:

  • DIN # : Used for German standards having mainly domestic significance or designed as the primary step toward international status.
  • DIN EN # : Used for the German edition of European standards.
  • DIN ISO # : Used for the German edition of ISO standards.
  • 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

Hose Size InNominal ID Inch Dash SizeStandard Dash Size
1 ½--
1 ¼1 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

  • 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.

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,…)

ASME B16.49 Factory Made Wrought Steel Butt welding Induction Bends for Transportation and Distribution Systems

ASME B16.49 Standard covers design, material, manufacturing, testing, marking, and inspection requirements for factory-made pipeline bends of carbon steel materials having controlled chemistry and mechanical properties, produced by the induction bending process, with or without tangents. This standard covers induction bends for transportation and distribution piping applications (e.g., ASME B31.4, B31.8, and B31.11). Process and power piping have differing requirements and materials that may not be appropriate for the restrictions and examinations described herein, and therefore are not included in this Standard.

Manufacturing Process

This process utilizes induction heating to heat a narrow band 360 deg around a pipe or cylinder at the point of bending as the pipe or cylinder is being pushed through the inductor coil at a constant velocity. After the material passes through the coil, it may be cooled by forced air or water spray, or it may be allowed to cool in the air. Bends in any producible wall thickness and diameter are covered. Induction bends covered by this Standard may be produced from seamless pipes, welded pipes, or cylinders.

Fabricated Bends

Larger angle bends obtained by girth welding two or smaller angle bends together are considered pipe fabrications and as such, are not within the scope of this Standard.

Standard Units

The values of This Standard state in both SI (Metric) and U.S. Customary units. These systems of units are to be regarded separately as standard. Within the text, the U.S. Customary units are shown in parentheses. The values stated in each system are not exact equivalents; therefore, it is required that each system of units be used independently of the other. Combining values from the two systems constitutes nonconformance with the Standard.


Standards and specifications adopted by reference in this Standard are shown in Mandatory Appendix I. It is not practical to identify the specific edition of each standard and specification in the individual references. Instead, the specific edition reference is identified in Mandatory Appendix I. A product made in conformance with a prior edition of reference standards and in all other respects conforming to this Standard will be considered to be in compliance.

Codes and Regulations

A bend used under the jurisdiction of a referencing code or governmental regulation is subject to any limitation of that code or regulation. This includes any maximum temperature limitation or rule governing the use of a material at low temperatures.

Service Conditions

Criteria for the selection of bend material for a particular fluid service are not within the scope of this Standard.


For determining conformance with this Standard, the convention for fixing significant digits where limits (maximum and minimum values) are specified shall be defined in ASTM E29. This requires that an observed or calculated value be rounded off to the nearest unit in the last right-hand digit used for expressing the limit. Decimal values and tolerances do not imply a particular method of measurement.

Quality Systems

Requirements relating to the manufacturers’ quality system programs are described in Nonmandatory Appendix A.


Bend qualification procedure: a document that specifies the properties of the starting pipe; equipment to be used; the bending parameters; the qualification bend test results; and the post bend, heat-treat equipment, and cycle used for the manufacture of the bends. If non-destructive testing of the bend is required, procedures that have not been approved previously shall be submitted.

  • cylinder: a joint of pipe produced by a rolling and welding plate, as opposed to a joint of pipe produced in accordance with a recognized specification.
  • extrados: the outside arc of the bend.
  • intrados: the inside arc of the bend.

minimum (design) wall thickness: the wall thickness specified or computed in accordance with the piping code as the minimum acceptable for the temperature and pressure application.

nominal (design) wall thickness: the wall thickness specified on the order or marked on the bend. ovality, %: [(O.D. max. − O.D. min.)/(O.D. nom)] × 100, where O.D. is a linear measurement of the maximum, minimum, or nominal outside diameter.

qualification bend: a bend segment that is produced and tested, and is used to qualify the bending procedure.

transition zone: the area, at the tangent points of a bend, that covers the change (transition) from unheated to heated material.

NOTE: The terms bender and manufacturer are used interchangeably in this Standard.

Bend Dimensional Terms

asme b1649 bend dimensional terms

Tensile Properties

asme b1649 tensile properties

General note:
Intermediate grades may be purchased subject to agreement between the purchaser and manufacturer.


HBW(Hardness Brinell) is the primary number.

HRC(Hardness Rockwell C) is an approximation based on ASTM E140 hardness conversion.

Maximum limits of chemical elements that may be used

ElementSymbolMaximum, %
The chemical requirements of this Table are not intended to represent the composition of any heat of steel, but to record the maximum permissible amounts of individual elements.

Test specimen locations and orientations – Longitudinal seam

asme b1649 test specimen locations and orientations

Test specimen locations and orientations – Helical seam

asme b1649 test specimen locations and orientations helical seam

Measurment of bend angle and out of squareness

asme b1649 measurment of bend angle and out of squareness
asme b1649 measurment of bend angle and out of squareness2