How to get high quality pipe bend?

What is a pipe bend?

Curva de tubo is a type of pipe fitting product for any offset or change of direction in the piping systems. It signifies that there is a “bend” i.e,  a change in direction of the piping (usually for some specific reason) – but it lacks specific, engineering definition as to direction and degree. Bends are usually made by using a bending machine (hot bending and cold bending) on site and suited for a specific need. Use of pipe bends are economic as it reduces number of expensive fittings.

Type of Pipe bend

A pipe bend means a piece of pipe which are bent to some angle to join two pipings. they can be nearly any bending radius and angles . Pipe bends are commonly produced on site to meet a specific need by hot induction bending or cold bending. A elbow means a specific pipe bend as per the standard ANSI/ASME B16.9 (or EN 10253, or other pipe fittings standards). Commonly the elbows have a bending radius of 1.5D or 1D (Here the D means nominal diameter of this bend) ,which are called “Long Radius elbow (LR elbow)” or “Short Radius elbow(SR elbow)” . and the angle of an elbow is 45 degree or 90 degree usually, some times there are also custom-designed elbows which are 30 degree,60 degree ,180 degree or other angles.

The pipe bends should be as per the standard of ANSI/ASME B16.49 which did not specific the bending radius and angle , the regular pipe bend radius are 2.5D, 3D ,5D ,7D or 8D , but it can be any other bending radius according to the design need, and bending angle can be in any degree, 5 ,10 ,15, 90 degree or any other. People said “All bends are elbows but all elbows are not bend”, it is not true . Actually “All elbows are pipe bends but not all bends are elbows” is more reasonable.

3D pipe bend : A 3D pipe bend is a pipe bend that the bend radius is 3 times the pipe outside diameter. 5D curva de tubo : The RADIUS of a 5D pipe bend is actually what is 5 times the nominal diameter. So if you had a 10″ diameter pipe, the radius of the centerline of the bend would be 50 inches. 7D curva de tubo 12D curva de tubo 180 Degree pipe bend

Small size curva de tubo: Small size pipe bending is a pipe bend that the bend radius is 3 times the pipe outside diameter. Large size curva de tubo: The large size pipe bending is used to change the direction of run of pipe. Butt-welded curva de tubo Sin fisuras curva de tubo High pressure curva de tubo: A High pressure pipe bending is a pipe bend that used in high pressure application.

Pipe bend, Bend pipe, Pipe bending, ANSI, ISO, JIS and DIN Standards, Measures 1/2 to 48 Inches.

Patrón	figure
Tamaño nominal	1/2"-48" (DN15-DN1200)
Grosor de la pared	2-100mm
Angle	Degree15,20,45,60,90,135,180
Tipo	3, 4, 5, 6, 7, 8, 10, 45, 90 and 180D

Material

They are manufactured utilizing higher grade raw material, advanced machines and technologies.

• Carbon steel:
  • SA234 WPB, SA234 WPC,SA42 WPL6, SA42 WPL3
  • WP1. MSS-SP75, WPHY,WPHY 46,WPHY 52
  • WPHY 56,WPHY 60,WPHY 65, WPHY 70
  • DIN 1629 St37, RST37.2 St52, STPG38
• Stainless:
  • ASTM/ASME SA403 304,304L ,316, 316L, WP304L, 3 WP316 WP347 (H) ,WP317 (L),WP321.
  • DIN 1.4301, 1.4306, 1.4401, 1.4571
  • JIS SUS304,SUS304, SUS304L, SUS316, SUS316
• Alloy:
• ASTM/ASME SA234 WP12, WP11,WP22, WP5, WP9, WP91, ASTM B361 GR.3003-6061, ASTM B366 UNS
• N04400,N08800, N08825 N1001-N10276-N10665, WPT2-WPT12
• ASTM 182 F1, F5, F6, F7, F9, F11, F12, F22, F51, 16MnR Cr5Mo
• 12Cr1MoV 10CrMo910 15CrMo 12Cr2Mo1, St45.8

Elbows Or Pipe Bends Manufacturing Process:

Método del mandril (conformado en caliente)

• One of the most common Pipe Fittings Manufacturing Process for manufacturing Elbows Or Pipe Bends from the pipe is mandrel method which is kind of hot forming methods.
• En este método, el tubo se corta en trozos y se empuja con ayuda de un ariete hidráulico. Se empuja sobre una matriz llamada "mandril" que permite que el tubo se expanda y se doble simultáneamente.
• This method can be used to manufacture a wide range of the diameter of codos or pipe bends
• 
  
• ELBOWS Or Pipe Bends Mandrel method

Método de extrusión

In cold Extrusion method, a pipe with the same diameter as finished product is pushed through a die and formed into its desired shape. Usually applied to stainless steel small to medium sizes elbows or pipe bends.

Método de extrusión

Método UO

UO method is used to manufacture medium size of the elbow, tee, and reducers. The plate is cut out into a specially designed shape, it is formed first into a U-shape using a die and then into an O-shape or tubular form using another die, that is why this method is known as UO method. Once the fittings formed in tumbler shaped it is welded from inside and outside of the closing seam. A cut plate is 1st from in U shape and then in O shape.

Método UO

Método de conformado en caliente

En el método de doblado con matriz de conformado en caliente, se calienta un tubo hasta la temperatura de conformado y se moldea en la matriz con la forma específica; este proceso puede repetirse según sea necesario para obtener la forma, el tamaño y el grosor de pared requeridos. Suele aplicarse a artículos de pared gruesa que no pueden doblarse en una matriz con mandril.

Hot Forming method for elbow or pipe bend Manufacturing

How to Calculate a Pipe Bend

Whether you are bending pipe for running electrical conduit or a metal project, calculating the bend for the start and end point can be an important factor. While there are different types of pipe benders on the market, they all share a common identification for the operation. Identified on all pipe benders is the size of pipe the unit will bend along with a number called the “take up.” The take up measurement is used for adding or deducting an allowance in the overall length of the bend. By following a basic process, you can calculate pipe bends regardless of the type of bender or the diameter of pipe.

Identify the take up measurement that is located on the pipe-bending shoe itself. This is the addition or deduction of measurement to the length of pipe from the front mark on the bending shoe. Also be aware that there is a second center-of-bend mark located approximately in the center of the bending shoe. Also located along the running length of the shoe are angle markings with lines. These numbers and lines correspond to actual angles that can be bent into the pipe by aligning the pipe with the angled line marked on the outside of the shoe.

Bend a 90-degree angle on a ½-diameter pipe with a ½-inch bender. The process will remain the same for different sized pipes and benders, but only the take up measurement will be different. Identified on the shoe for the ½-inch pipe may be the wording “stub take up 5 inches from arrow or line.” The 5 inches is the amount you will deduct from the overall length of the 90-degree bend measurement.

Use the measuring tape and pencil and place a mark at 12 inches from the end of the pipe. This will be the distance from the bend to the end of the pipe. By using the deduction measurement on the shoe, measure back 5 inches from the 12-inch mark and make a solid pencil line.

Lay the pipe on a level surface and insert the pipe into the bender. The solid pencil mark should be placed 5 inches back from the 12-inch mark and should be aligned with the front mark or arrow on the bending shoe. Pull back on the handle in a smooth motion until the pipe sits at a 90-degree position to the level surface. Place the small level against the upright portion of the pipe and check for level. This will give you a perfect 90-degree bend. Check the height of the overall bend by placing the end of the tape measure on the level base and measure the end of the pipe. It should read 12 inches exactly.

Practice with other angled bends by using the deduction measurement and the center of the bend mark on the shoe. All pipe benders may have their own quirks and slight measurement adjustments that will have to be done. The actual end result also depends on how well and secure you hold the pipe in the bender, prior to the first bend you place on the pipe.

What is an elbow?

Elbow angle can be easily calculated using simple geometrical technique of mathematics. Lets give an example for you. Refer to Fig.2. Pipe direction is changing at point A with the help of an elbow and again the direction is changing at the point G using another elbow.

Fig.3: Code equation for minimum thickness requirement calculation

Here,

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:

What is the difference between a Pipe Bend and an elbow?

The difference between them is as follows:

1. Bend is a generic term for any offset or change of direction in the piping. It is a vague term that also includes elbows.
2. Un codo es un término de ingeniería y se clasifican en 90 grados o 45 grados, de radio corto o largo.
3. Elbows have industrial standards and have limitations to size, bend radius and angle. The angles are usually 45 deg or 90 degrees. All others offsets are classified as pipe bends.
4. Las curvas se suelen hacer o fabricar según las necesidades de la tubería; sin embargo, los codos son prefabricados y estándar, y están disponibles en stock.
5. Las curvas nunca son ángulos agudos, pero los codos sí. Las técnicas de curvado de tuberías tienen limitaciones en cuanto al adelgazamiento del material para contener con seguridad la presión del fluido. Como los codos son prefabricados, fundidos o soldados a tope, pueden ser afilados, como los ángulos rectos y los codos de retorno, que son de 180 grados.
6. El codo es un accesorio estándar, pero los codos se fabrican a medida.
7. En los codos, como la tubería está doblada y no hay soldadura, hay menos fricción en la tubería y el flujo es más suave. En los codos, la soldadura puede crear cierta fricción.
8. Todos los codos son curvas, pero todas las curvas no son codos.
9. La curva tiene un radio mayor que los codos.
10. Generalmente, la diferencia más básica es el radio de curvatura. Los codos suelen tener un radio de curvatura entre uno y dos veces el diámetro de la tubería. Las curvas tienen un radio de curvatura superior al doble del diámetro.

Short Radius and Long Radius

Elbows are again classified as long radius or short radius elbows. The difference between them is the length and curvature. A short radius elbow will be giving the piping a sharper turn than a long radius elbow.

1. In a long radius elbow the radius of curvature is 1.5 times the nominal diameter. In a standard elbow the radius of curvature is 1.0 times the nominal diameter of the pipe.
2. Long radius elbows give less frictional resistance to the fluid than the short elbows.
3. Long radius elbows create lesser pressure drop than short radius elbows.
4. Short radius is less costly than long radius elbows.
5. The short radius elbows are used where there is scarcity of space.

In addition to this classification the elbows are 45 degrees, 90 degrees and 180 degrees also called as a return elbow.

The 45 degrees elbow turns the fluid /piping at 45 degrees and so on.

Miter bends

Another type of bend is a Miter bend. A Miter bend is a bend which is made by cutting pipe ends at an angle and joining the pipe ends. A true miter bend is a 90 degree bend made by cutting two pipes at 45 degrees and joining them by welding.  Similarly three pipes cut at 22.5 degrees will give a 90 degree miter bend.

In the next article we will discuss about various pipe fittings.

“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.

Sharp bends are normally called Elbows. 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 & 4.5 R are the most common bending radii in industry.

An “elbow” and a “bend” are two different animals – as the terms are generally employed in the process industry.

A BEND is the generic term for what is called in piping as an “offset” – a change in direction of the piping. A bend is usually meant to mean nothing more than that there is a “bend” – a change in direction of the piping (usually for some specific reason) – but it lacks specific, engineering definition as to direction and degree. Bends are usually custom-made (using a bending machine) on site and suited for a specific need.

An ELBOW, on the other hand, is a specific, standard, engineered bend pre-fabricated as a spool piece and designed to either be screwed, flanged, or welded to the piping it is associated with. An elbow can be 45Deg or 90Deg. There can also be custom-designed elbows, although most are catagorized as either “short radius” or long radius”.

A bend can be an elbow; an elbow does not mean a bend. If you use the term elbow, it should also carry the qualifiers of type (45 or 90Deg) and radius (short or long) – besides the nominal size.

Additionally, if you are using tube and not pipe, there is a marked difference. As you can bend tube for pressure applications you will get less interuption and turbulence in your flow; this translates to less pressure drop than with fitted 90 or 45Deg elbows.

Long radius elbow is used to change the direction of flow gradually, 90 degrees.

• Short radius elbow is used to change the direction of flow rapidly, 90 degrees.
• 45° elbow is used to change the flow only 45°.
• Return bends are used to change the direction of flow 180°.

Processing:

The physical difference between Long Radius and Short Radius Elbows is graphically illustrated in the attached Workbook that I have put together for this thread.

The following is the criteria I use when deciding which to use:

Long Radius Elbows are used when:

• 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;
• the fluid being transported is abrasive or has solids in it.

Short Radius Elbows are used when:

• there is a need to reduce the cost of elbows;
• there is a scarcity of space and volume to allow a Long Radius type.

Fuente: China Tubería Curva Manufacturer - Yaang Pipe Industry Co., Limited (www.ugsteelmill.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Referencias:

• https://www.marineinsight.com/tech/pipeing/pipes-and-bends-an-essential-guide-for-second-engineers-part-2/
• http://www.whatispiping.com/piping-elbows-and-bends
• https://www.yaang.com
• https://hardhatengineer.com/pipe-fittings/pipe-fittings-manufacturing-process/