ASTM A234 is the industry standard and typical specification for carbon steel fittings.
It is intended for use in pressure piping systems at moderate to high temperature services that "covers wrought carbon steel and alloy steel fittings," according to ASTM. These fittings are used in various industries and applications, such as O&G, power generation, chemical processing and more.
Since my father-in-law, David Hatfield, CEO of OK Pipe & Fittings, began his career in the pipe valve and fitting (PVF) industry almost 50 years ago, laterals have been excluded from this classification, yet they are seen on bills of material and used for internal product codes more often than not.
To underscore the elimination of laterals from ASTM A234 and ASME B16.9 standards, the corresponding dimensional spec declares, on page one, paragraph 1.3, "Fabricated laterals … are not within the scope of this standard." No other specs are implied.
Laterals are something of an enigma because they have the nature of a fitting, more specifically, a tee lateral. They cannot be forged or wrought in any way, except for ductile iron or other casting or A105 machining — they must be fabricated. Wrought, in this sense, means hot formed.
Forty-five-degree laterals are used in low pressure piping systems where a new branch line is installed perpendicular to an existing pipeline — a unique fabrication allowing the diversion of the flow of fluid to the lateral line for efficient delivery to the desired destination. Fabricated in equal sizes or reducing sizes depending on the branch size the pipeline requires; these fittings can be fabricated in almost any schedule of the matching A106 pipe. Laterals are an essential component of the pipe fittings industry, allowing custom fabricated branch connections to direct fluid efficiently. Predominantly used in water applications due to the low-pressure ratings, fabricated laterals have been installed in children’s hospitals, naval water transfer for ship repair, chip plant construction and hundreds of other projects requiring the redirection and transfer of liquids and gases.
Forty-five-degree laterals are rated at 40% of the maximum allowable working pressure of the matching pipe. When a hole is cut into pipe, it loses its hoop stress — the circumferential force applied around the inside of the pipe. Hoop stresses are the tensile generated to resist the bursting effect resulting from the application of pressure. Once a hole is cut, this disrupts the uniformity of the pressure applied, decreasing the pressure the fitting can now handle to 40% of the matching pipe.
A234 WPB is also requested for welded laterals. W means weldable, P stands for pressure and B for the grade of material, referring to the minimum yield strength. A welded lateral cannot be classified as WPB, as laterals cannot be wrought. A WPB fitting is weldable, meaning it can be welded to other fittings or A106 B pipe, but a welded lateral does not meet the requirements of A234 WPB.
Certain activities can be added to fabricated laterals to mimic A234. They can be reinforced, heat treated and X-rayed or ultrasonically tested to meet a supplement of A234, but this is only possible because the reinforcement is wrought, or formed, and is often used as a less expensive alternative. For reinforcement, a custom fabricated saddle is welded onto the run and branch connection weld of the lateral and 100% X-rayed, reinforcing the original weld.
Some claim that laterals are not a fitting at all but a branch connection subject to ASME B31.1, which is focused on power plant piping systems, or B31.3, which is used for process piping systems in a broader range of industries. This, of course, complicates things even further as it would require different levels of reinforcement specific to that project, making providing these as an industry standard impossible.
A major player in the PVF industry, OK Pipe & Fittings has been fabricating laterals for more than 25 years. We offer fabrication of laterals in carbon and stainless steel, and in various wall thicknesses and even custom lengths for master distribution throughout the U.S., Canada and Mexico.
For more information, visit pvfroundtable.org.
