Pipe elbows are used to change the direction of the pipeline by a given angle, typically 45, 90 or 180 degrees. In this article, we define steel elbows, show the available types, material grades, and sizes. Steel elbows are manufactured according to ASME B16.28 (short radius elbows and short radius 180 degrees elbows), ASME B16.9 and MSS SP 43 (stainless steel elbows).
DEFINITION AND USE
Pipe elbows are butt weld fittings used to change the direction of a pipeline by specific degrees (typically 45°, 90° or 180°).
The relevant ASME specifications for pipe elbows are:
- ASME B16.28: Short radius elbows and returns)
- ASME B16.9: carbon/alloy steel long radius elbows and returns
- ANSI B16.9 and MSS SP 43: stainless steel and alloy-steel elbows
- ASME B16.25: buttwelding ends specifications
These specifications define the standard sizes and tolerances of butt weld elbows (and other pipe fittings that require welding).
The image shows the differences between 45, 90 and, 180 degrees elbows for pipelines.
PIPE ELBOWS DIMENSIONS
Elbows are available in a wide range of dimensions (combination of outside diameter and wall thickness, i.e. schedule) to fit the needs of pipelines of sizes from 1 to 80 inches and above (elbows size chart is available in this article). Elbows are manufactured out of seamless steel pipes up to 24 inches in diameter and using welded pipes or plates for higher sizes. Elbows of very large diameters are called “mitered elbows” (see image below).
ELBOWS MATERIAL GRADES
The typical material grades for butt weld elbows are carbon steel (ASTM A234 WPA/WPB/WPC), alloy steel for power generation (ASTM A234 WP9/WP91 and other low-alloy grades), stainless steel (ASTM A403 WP304/WP 316 and so on) and, duplex/super duplex (ASTM A815 UNS S31803 and UNS S32750/32760). Nickel alloys like Inconel, Hastelloy, Incoloy are also used to manufacture pipe elbows.
Carbon steel elbows ASTM A234 WPB, WPC – chemical composition:
Stainless steel elbows ASTM A403 304, 316 – chemical composition:
In addition to standard elbows, reducing elbows (fittings that have different diameters at the inlet and outlet sides) are also available. Reducer elbows are used when the use of a more standard combination of an elbow and a reducer is not possible due to space constraints.
Example of reducing elbow, having on bore size smaller than the other one.
PIPE ELBOWS MANUFACTURING PROCESS
DIFFERENCE BETWEEN SHORT AND LONG RADIUS ELBOWS
The center to face distance of long radius elbow (see “B” in the image below) is always 1.5 times the nominal pipe size, whereas, for short radius elbows, the center to face distance (see “A” in the image) is equal to the nominal pipe size.
- For a 4 inches long radius (LR) elbow, the center to face distance is 4 x 25.4 x 1.5 = 152.4 mm;
- For a SR elbow the center to face distance is instead 4 x 25.4 x 1 = 101.6 mm. Short radius elbows are available only for the 90 and 180-degree configuration (and not for the 45 degrees); instead, long radius elbows are available for all degrees.