Definition of Pipe elbow

An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made. The ends may be machined for butt welding, threaded (usually female), or socketed, etc. When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.

An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 180° or 90° angle, though 45° elbows are also made. The ends may be machined for butt welding (SW) or socketed welding(SW) etc.

Most elbows are available in short radius or long radius variants. When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.

elbow cs as per api 5l x52 psl1


Carbon steel elbow

Carbon steel elbow

stainless elbows

Stainless elbows

  • ASTM/ASME A403 WP 304-304L-304H-304LN-304N
  • ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti
  • ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H

Types of Elbow in Piping

90 Degree Elbow
A 90 Degree Elbow is placed between the pipes to change the direction of the pipe by 90 degrees. There are both long and short radius choices.

45 Degree Elbow
A 45 Degree Elbow is placed between the pipes to change the pipe’s direction by 45 degrees.

Long Radius Elbow
A Long Radius Elbow centerline radius is 1.5 times the pipe’s nominal size, or 1.5 times the pipe’s diameter. Because long radius elbows have less pressure loss than short radius elbows, they are often utilized in pipes. It required more space than a short radius elbow.

Short Radius Elbow
A Short Radius Elbow centreline radius is equal to the pipe’s nominal size, or one time the pipe’s diameter. Short radius elbows are used in applications where space is limited. It does, however, show a high-pressure drop owing to a rapid change in the flow direction.

Reducing Elbow
The 90 Reducing Elbow is used to alter the direction of a pipe while also lowering its size in a piping system. The reducing elbow replaces one pipe fitting and cuts welding time by more than a third. In addition, the decreasing elbow’s steady decline in diameter over its arc minimizes flow resistance and lessens the influence of stream turbulence and probable internal erosion. These characteristics prevent the line from experiencing significant pressure drops.

LR or SR elbow to use?

L/R – Long radius, S/R – Short radius

  • The short radius elbow is used in tight areas, while the long radius is used under normal working conditions.
  • The long radius elbow is better than short radius elbow when it is scoured and worn.
  • The position of the two elbows should be determined according to the practical conditions, because the positions are necessary.
  • The reducing elbow eliminates one pipe fitting and reduces the welding by more than one-third.

Elbows are design features as below

  • 90 Degree Elbow – where change in direction required is 90°
  • 45 Degree Elbow – where change in direction required is 45°


  • A wing of a building at right angles to the main structure.
  • A right-angled bend in a pipe or conduit; an elbow.

” All bends are elbows but all elbows are not bends.”

Infact, the pipe is bent to form an elbow.

Elbows are pre-fabricated and are firm in design.

There are issues with bends since the tickness at the bend radius reduces as we bend the pipe.

Bends typically have a minimum bending radius of 1.5 times pipe radius (R). If this bending radius is less than 1.5R, it is called Elbow. Reference to any international / industry standard need to be traced. 1.5, 3 and 4.5 R are the most common bending radii in industry.
An elbow is also typically a sharp 90 degrees and often is a separate piece.

Sharp bends are normally called Elbows.

An elbow is also typically a sharp 90 degrees and often is a separate piece.

A bend is typically of the same material and typically a more gentle bend to prevent kinking.

A bend typically flows smoother since there are not irregular surfaces on the inside of the pipe, nor does the fluid have to change direction abruptly.

The most basic difference of them is the elbow relatively short than bend, R = 1D to 2 D is elbow More than 2D is bend. In the production process, cold bends can use Bending Machine to bend by ready-made straight bend. One-time completed also don’t need second corrosion. But elbow need manufacturers make to order, to do anti-corrosion, order cycle is long. Elbow price is higher than bend. But cost performance is much higher than bend. It is well-known that bend do not have anticorrosive processing is easy damaged, but the price is cheap so are used very much in some demand which not very high engineering.

In the west-east gas transmission of course, cold bends cost is low. elbow need manufacturers make to order, needs corrosion, order cycle is long,but cold bends can use ready-made straight bend by Bending Machine to bend. One-time completed also don’t need second corrosion. The cold bend construction technology need follow oil standard .west-east gas transmission have the enterprise standard,but we can use either elbow nor bend in open area. Sunny Steel Enterprise warn broad customers betweenness elbow and bend performance price is differ ,please carefully choose after consider it.

Elbow angle can be easily calculated using simple geometrical technique of mathematics.

Elbow Radius

Elbows or bends are available in various radii for a smooth change in direction which are expressed in terms of pipe nominal size expressed in inches. Elbows or bends are available in three radii,

a. Long radius elbows (Radius = 1.5D): used most frequently where there is a need to keep the frictional fluid pressure loss down to a minimum, there is ample space and volume to allow for a wider turn and generate less pressure drop.

b. Long radius elbows (Radius > 1.5D): Used sometimes for specific applications for transporting high viscous fluids likes slurry, low polymer etc. For radius more than 1.5D pipe bends are usually used and these can be made to any radius.However, 3D & 5D pipe bends are most commonly used

b. Short radius elbows (Radius = 1.0D): to be used only in locations where space does not permit use of long radies elbow and there is a need to reduce the cost of elbows. In jacketed piping the short radius elbow is used for the core pipe.

Here D is nominal pipe size in inches.

There are three major parameters which dictates the radius selection for elbow. Space availability, cost and pressure drop.

Pipe bends are preferred where pressure drop is of a major consideration.

Use of short radius elbows should be avoided as far as possible due to abrupt change in direction causing high pressure drop.

code equation for minimum thickness requirement calculation

Minimum thickness requirement

Whether an elbow or bend is used the minimum thickness requirement from code must be met. Code ASME B 31.3 provides equation for calculating minimum thickness required (t) in finished form for a given internal design pressure (P) as shown below:

R1 = bend radius of welding elbow or pipe bend
D = outside diameter of pipe
W = weld joint strength reduction factor
Y = coefficient from Code Table 304.1.1
S = stress value for material from Table A-1 at maximum temperature
E = quality factor from Table A-1A or A-1B

Add any corrosion, erosion, mechanical allowances with this calculated value to get the thickness required.

a typical butt welded elbow

End Connections

For connecting elbow/bend to pipe the following type of end connections are available

  • Butt welded: Used alongwith large bore (>=2 inch) piping
  • Socket welded: Used alongwith pipe size
  • Screwed
  • Flanged

Butt welded Elbows

  • Pipe is connected to butt welded elbow as shown in Fig. 4 by having a butt-welding joint.
  • Butt welded fittings are supplied with bevel ends suitable for welding to pipe. It is important to indicate the connected pipe thickness /schedule while ordering. All edge preparations for butt welding should conform to ASME B16.25.
  • Dimensions of butt welded elbows are as per ASME B16.9. This standard is applicable for carbon steel & alloy steel butt weld fittings of NPS 1/2” through 48”.
  • Dimensions of stainless steel butt welded fittings are as per MSS-SP-43. Physical dimensions for fittings are identical under ASME B16.9 and MSS-SP-43. It is implied that the scope of ASME B16.9 deals primarily with the wall thicknesses which are common to carbon and low alloy steel piping, whereas MSS-SP-43 deals specifically with schedule 5S & 10S in stainless steel piping.
  • Dimensions for short radius elbows are as per ASME B16.28 in case of carbon steel & low alloy steel and MSS-SP-59 for stainless steel.
  • Butt welded fittings are usually used for sizes 2” & above. However, for smaller sizes up to 1-1/2” on critical lines where use of socket welded joints is prohibited, pipe bends are normally used. These bends are usually of 5D radius and made at site by cold bending of pipe. Alternatively, butt welded elbows can be used in lieu of pipe bends but usually smaller dia lines are field routed and it is not possible to have the requirement known at initial stage of the project for procurement purpose. So pipe bends are preferred. However, pipe bends do occupy more space and particularly in pharmaceutical plants where major portion of piping is of small dia. and layout is congested, butt welded elbows are preferred.
  • Butt welded joints can be radiographed and hence preferred for all critical services.

Elbows are split into two groups which define the distance over which they change direction; the center line of one end to the opposite face.

This is known as the “center to face” distance and is equivalent to the radius through which the elbow is bent.

Here below, for example, you will find the center to face distance of NPS 2 elbows (the A distance on the image)

  • 90°-LR : = 1½ x 2(NPS) x 25.4 A=76.2 mm
  • 180°-LR : = 2 times the 90° LR elbow A=152.4 mm
  • 90°-SR : = 2(NPS) x 25.4 A=50.8 mm
  • 180°-SR : = 2 times the 90° SR elbow A=101.6 mm

The center to face distance for a “long” radius elbow, abbreviated LR always is “1½ x Nominal Pipe Size (NPS) (1½D)”, while the center to face distance for a “short” radius elbow, abbreviated SR even is to nominal pipe size.