Most of the standards covering pipe and fittings manufactured by AMERICAN Cast Iron Pipe Company have been prepared by the American Water Works Association Standards Committee A21. Other applicable standards generally cover specialties or refer to ANSI standards.

To take advantage of modern metallurgical science, better testing methods, improved production control, materials with better physical properties, and improvements in manufacturing methods, the A21 Committee has a continuing program to keep its standards revised to include the latest developments.

The AWWA Standards Committee A21 on Ductile and Gray Iron Pipe and Fittings was organized in 1926 under the procedures of the American Engineering Standards Committee. It was reorganized under American Standards Association Procedures in 1955, and in 1984 it became a member of the AWWA committee structure.

The committee is responsible for the development of standards and manuals for ductile iron pressure pipe for water and other liquids and for fittings used with such pipe. The committee’s membership is comprised of representatives from consumer groups, producer groups and general interest groups, including a number of professionals from AMERICAN.

A standard, manual or revision is developed by a subcommittee assigned to that task. The subcommittee prepares and submits the document to the Standards Committee for approval. After approval it is submitted to the AWWA Standards Council for approval. After all approvals have been received, including a public review by both AWWA and ANSI, the standard, manual or revision is published and made available to the public.

The following is a list of the organizations referred to in this and other sections of this website by abbreviation:

A brief review of the older specifications in chronological order may help define their usefulness, as well as help in the appreciation of the improved modern standards.

The basis for design in almost all specifications to date is the Barlow formula, or "Hoop Stress" formula. It embodies the basic principle for design of a cylinder for internal pressure. The formula may be stated as t= PD/2S in which t is the thickness of the pipe in inches; P is the internal pressure in pounds per square inch (psi); D is the outside diameter in inches; and S is the allowable working stress of the metal in pounds per square inch.

In the development of the design of cast iron pipe, this formula has been modified in several ways by prominent water works engineers such as Allen Hazen, Thomas H. Wiggin, James T. Fanning, Dexter Brackett, I. J. Fairchild and James P. Kirkwood. Mr. Kirkwood, as chief engineer for the Brooklyn Water Works, developed a design for cast iron pipe that was a variant of the Barlow formula. Kirkwood’s calculations took into consideration casting imperfection, strength of the metal and other factors affecting the life of the pipe. In the late 1880s, a formula by Dexter Brackett, distribution engineer for the City of Boston, was adopted by the New England Water Works Association as its standard.

Although the 1902 NEWWA standards did not provide a formula for pipe thicknesses, the Brackett formula was used in determining the thicknesses recommended.

In 1908, AWWA adopted a standard covering bell and spigot pipe produced in 12-foot laying lengths by the pit casting method. Prior to 1908, at least two unofficial documents dealing with pipe design were acknowledged by AWWA. The first of these used thicknesses for pipe determined by averaging the thicknesses used in a large number of American cities. The second dealt with actual design of pipe based on Brackett’s method with variations.

The 1908 AWWA standards employed a system of class designations applied to specific wall thicknesses in diameters 4" to 84" inclusive for a range of hydraulic heads. The most common of these classes were A, B, C and D for 100, 200, 300 and 400 feet hydraulic head, respectively. The design was based on a variation of the Brackett formula by J. T. Fanning and included a variation in the outside diameter for the different classes of pipe. The basic design of pipe with a different outside diameter for each class was followed in modern specifications until the 1961 revisions. The general acceptance by the water works industry of the standardized mechanical joint necessitated a universal outside diameter for cast iron pipe.

AWWA revised its standards in 1939 to incorporate a new method of designing cast iron pressure pipe. This new method was published as ANSI A21.1. The A21.1 method of determining the required thickness of cast iron pipe took into consideration trench load and internal pressure in combination. Trench load consists of the earth load on the pipe plus any transient load resulting from traffic over the trench; internal pressure consists of the design working pressure plus an additional allowance for surge pressure. Laying conditions and properties of the iron in the pipe are also factors involved in the design. Additions for casting tolerance are included in the design thickness. With the advent of ductile iron pipe and its flexibility, this additive method of design became obsolete. As noted in the following paragraph, ductile iron design employs flexible conduit principles since the internal pressure relieves the external load.

Actually, the first standard covering centrifugally cast pipe was issued by the U.S. government in 1927, and was known as  Federal Specification No. 537. In July 1931, the specification was revised to include pipe cast centrifugally in sand-lined molds, pipe cast centrifugally in metal molds and pit cast pipe. This specification has been modified several times and is now basically the same as ANSI/AWWA Standards.

Development of ductile iron in the 1950s initiated research into design of ductile iron pipe to take advantage of the superior flexibility, strength, toughness, impact resistance and corrosion resistance of this new metal. The A21 Committee issued the ANSI A21.50 (AWWA H3-65) and ANSI A21.51 (AWWA C151) Standards for ductile iron pipe in 1965. The work of M. G. Spangler and others at Iowa State University on flexible conduit is the basis for principles that have been applied extensively by the designers of flexible underground pipe. The design principles and procedures for ductile iron pipe that were included in the ANSI Standard A21.50 (AWWA C150) were verified by trench tests at AMERICAN and tests conducted by various researchers. AMERICAN’s former Technical Director Dr. Ed Sears was instrumental in these developments.

Continued research on ductile iron pipe reflects through these updated standards the advancements in metallurgical technology and manufacturing skills. Furthermore, the quality of AMERICAN’s products and conformance to appropriate specifications are assured by the British Standards Institute’s certification that AMERICAN’s quality system complies with ISO 9001 Quality Management System Standard.

AMERICAN also subscribes to NSF’s listing program for products under ANSI/NSF Standard 61 — Drinking Water System Components — Health Effects. Check with AMERICAN for current listing of our products.

Throughout this website, Standards may be referred to as listed below or by only the ANSI, AWWA, ASTM, NSF, ASME, etc. numbering.

Other joints shown in this section are AMERICAN design.

All Products1 ANSI/NSF Standard 61
NOTE: Many AMERICAN joints, classes of pipe, fittings and specials are listed by Underwriters Laboratories Inc. and FM Global. The quality of AMERICAN’s products and conformance to appropriate specifications are assured by the British Standards Institute’s certification that AMERICAN’s quality system complies with ISO 9001 Quality Management System Standard.