China piping solution supplier: www.epowermetals.com

# What is a pipe bend?

Pipe bend 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.

## Size range of pipe bend

The bend is used to change the direction of run of pipe.it advantage is can matach long distance transition requirements,so it is commonly that bends dimension according to customer design.

usually,the bends consist of 3D,5D,7D even 12D series.carbon steel bend

## Constants for Pipe Bends

Formula: L = R x B (L = Length of pipe required, R = Radius of bend, B = Constant from table used to find “L”, L =30 x 1.5705 =47.115 in.or 47-1/8″)
Example: Find the length of pipe required to make a 90 bend with a radius of 30″

 Nominal pipe DN size Outside Diameter at Bevel Center to End D1 D2 C M Series A Series B Series A Series B 20×15 26.9 25 21.3 18 29 29 25×20 25×15 33.7 33.7 32 32 26.9 21.3 25 18 38 38 38 38 32×25 32×20 32×15 42.4 42.4 42.4 38 38 38 33.7 26.9 21.3 32 25 18 48 48 48 48 48 48 40×32 40×25 40×20 40×15 48.3 48.3 48.3 48.3 45 45 45 45 42.4 33.7 26.7 21.3 38 32 25 18 57 57 57 57 57 57 57 57 50×40 50×32 50×25 50×20 60.3 60.3 60.3 60.3 57 57 57 57 48.3 42.4 33.7 26.9 45 38 32 25 64 64 64 64 60 57 51 44 65×50 65×40 65×32 65×25 76.1(73) 76.1(73) 76.1(73) 76.1(73) 76 76 76 76 60.3 48.3 42.4 33.7 57 45 38 32 76 76 76 76 70 67 64 57 80×65 80×50 80×40 80×32 88.9 88.9 88.9 88.9 89 89 89 89 76.1(73) 60.3 48.3 42.4 76 57 45 38 86 86 86 86 83 76 73 70 90×80 90×65 90×50 90×40 101.6 101.6 101.6 101.6 – – – – 88.9 76.1(73) 60.3 48.3 – – – – 95 95 95 95 92 89 83 79 100×90 100×80 100×65 100×50 100×40 114.3 114.3 114.3 114.3 114.3 – 108 108 108 108 101.6 88.9 76.1(73) 60.3 48.3 – 89 76 57 45 105 105 105 105 105 102 98 95 89 86 125×100 125×90 125×80 125×65 125×50 139.7 139.7 139.7 139.7 133 –  133 133 133 114.3 101.6 88.9 76.1(73) 60.3 108 – 89 76 57 124 124 124 124 124 117 114 111 108 105 150×125 150×100 150×90 150×80 150×65 168.3 168.3 168.3 168.3 168.3 159 159  – 159 159 139.7 114.3 101.6 88.9 76.1(73) 133 108 – 89 76 143 143 143 143 143 137 130 127 124 121 200×150 200×125 200×100 200×90 219.1 219.1 219.1 219.1 219 219 219 – 168.3 139.7 114.3 101.6 159 133 108 – 178 178 178 178 168 162 156 152 200×200 200×150 200×125 200×100 273.0 273.0 273.0 273.0 273 273 273 273 219.1 168.3 139.7 114.3 219 159 133 108 216 216 216 216 208 194 191 184 300×250 300×200 300×150 323.9 323.9 323.9 325 325 325 273.0 219.1 168.3 273 219 159 254 254 254 241 229 219 300×125 323.9 325 139.7 133 254 216 350×300 350×250 350×200 350×150 355.6 355.6 355.6 355.6 377 377 377 377 323.9 273.0 219.1 168.3 325 273 219 159 279 279 279 279 270 257 248 238 400×350 400×300 400×250 400×200 400×150 406.4 406.4 406.4 406.4 406.4 426 426 426 426 426 355.6 323.9 273.0 219.1 168.3 377 325 273 219 159 305 305 305 305 305 305 295 283 273 264 450×400 450×350 450×300 450×250 450×200 457.2 457.2 457.2 457.2 457.2 478 478 478 478 478 406.4 355.6 323.9 273.0 219.1 426 377 325 273 219 343 343 343 343 343 330 330 321 308 298 500×450 500×100 500×350 500×300 500×250 500×200 508.0 508.0 508.0 508.0 508.0 508.0 529 529 529 529 529 529 457.2 406.4 355.6 323.9 273.0 219.1 478 426 377 325 273 219 381 381 381 381 381 381 368 356 356 346 333 324 550×500 550×450 550×400 559 559 559 – – – 508 457 406 – – – 419 419 419 406 394 381 600×550 600×550 600×450 610 610 610 – 630 630 559 508 457 – 530 480 432 432 432 432 432 419 650×600 650×550 650×500 660 660 660 – – – 610 559 508 – – – 495 495 495 483 470 457 700×650 700×600 700×550 711 711 711 – 720 – 660 610 559 – 630 – 521 521 521 521 508 495 750×700 750×650 750×600 762 762 762 – – – 711 660 610 – – – 559 559 559 546 546 533 800×750 800×700 800×650 813 813 813 – 820 – 762 711 660 – 720 – 597 597 597 584 572 572 850×800 850×750 850×700 864 864 864 – – – 813 762 711 – – – 635 635 635 622 610 597 900×850 900×800 900×750 914 914 914 – 920 – 864 813 762 – 820  – 673 673 673 660 648 635 950×900 950×850 950×800 965 965 965 – – – 914 864 813 – – – 711 711 711 711 698 686 1000×950 1000×900 1000×8500 1016 1016 1016 – 1020 – 965 914 864 – 920  – 749 749 749 749 737 724 1000×1000 1050×950 1050×900 1067 1067 1067 – – – 1016 965 914 – – – 762 762 762 711 711 711 1100×1050 1100×1000 1100×950 1118 1118 1118 – 1120 – 1067 1016 965 – 1020  – 813 813 813 762 749 737 1150×1100 1150×1050 1150×1000 1168 1168 1168 – – – 1118 1067 1016 – – – 851 851 851 800 787 775 1200×1150 1200×1100 1200×1050 1220 1220 1220 – 1220 – 1168 1118 1067 – 1120  – 889 889 889 838 838 813
 Nominal pipe size Outside Diameter at Bevel Center to End D C M DN INCH Series A Series B 15 1/2 21.3 18 25 20 3/4 26.9 25 29 25 1 33.7 32 38 32 11/4 42.4 38 48 40 11/2 48.3 45 57 50 2 60.3 57 64 65 21/2 76.1(73) 76 76 80 3 88.9 89 86 90 31/2 101.6 ― 95 100 4 114.3 108 105 125 5 139.7 133 124 150 6 168.3 159 143 200 8 219.1 219 178 250 10 273.0 273 216 300 12 323.9 325 254 350 14 355.6 377 279 400 16 406.4 426 305 450 18 457.2 478 343 500 20 508.0 529 381 550 22 559 ― 419 600 24 610 630 432 650 26 660 ― 495 700 28 711 720 521 750 30 762 ― 559 800 32 813 820 597 850 34 864 ― 635 900 36 914 920 673 950 38 965 ― 711 1000 40 1016 1020 749 1050 42 1067 ― 762 711 1100 44 1118 1120 813 762 1150 46 1168 ― 851 800 1200 48 1220 1220 889 838

## 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 pipe bend : 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 pipe bend 12D pipe bend 180 Degree pipe bend Small size pipe bend: Small size pipe bending is a pipe bend that the bend radius is 3 times the pipe outside diameter. Large size pipe bend: The large size pipe bending is used to change the direction of run of pipe. Butt-welded pipe bend Seamless pipe bend High pressure pipe bend: 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.

 Pattern figure Nominal size 1/2”-48” (DN15-DN1200) Wall thickness 2-100mm Angle Degree15,20,45,60,90,135,180 Type 3, 4, 5, 6, 7, 8, 10, 45, 90 and 180D

## Material of pipe bend

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

## Manufacturing Process of Elbows Or Pipe Bends

### Mandrel method (Hot Forming)

• 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.
• In this method, the pipe is cut in pieces and push with the help of hydraulic ram. It is pushed over a die called “mandrel” which allows the pipe to expand and bend simultaneously.
• This method can be used to manufacture a wide range of the diameter of elbows or pipe bends

• ELBOWS Or Pipe Bends Mandrel method

### Extrusion Method

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.

Extrusion Method

### UO Method

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.

UO Method

### Hot Forming Method

In a Hot Forming Die Bending method, a Pipe is heated to forming temperature & formed in the die with the specific shape, this process may be repeated as needed to obtain the required shape, size and wall thickness. Usually applied to thick-wall items that cannot be bent on a mandrel die.

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?

An elbow, on the other hand, is a specific, standard, engineered bend pre-fabricated as a spool piece  (based on ASME B 16.9) and designed to either be screwed, flanged, or welded to the piping it is associated with. An elbow can be 45 degree or 90 degree. There can also be custom-designed elbows, although most are catagorized as either “short radius” or long radius”.

In short “All bends are elbows but all elbows are not bend”

Whenever the term elbow is used, it must also carry the qualifiers of type (45 or 90 degree) and radius (short or long) – besides the nominal size.

Elbows can change direction to any angle as per requirement. An elbow angle can be defined as the angle by which the flow direction deviates from its original flowing direction (See Fig.1 below).Even though An elbow angle can be anything greater than 0 but less or equal to 90°But still a change in direction greater than 90° at a single point is not desirable. Normally, a 45° and a 90° elbow combinedly used while making piping layouts for such situations.

Fig.1 A typical elbow with elbow angle (phi)

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.2 Example figure for elbow angle calculation
In order to find out the elbow angle at A, it is necessary to consider a plane which contains the arms of the elbow. If there had been no change in direction at point A, the pipe would have moved along line AD but pipe is moving along line AG. Plane AFGD contains lines AD and AG and elbow angle (phi) is marked which denotes the angle by which the flow is deviating from its original direction.
• Considering right angle triangle AGD, tan(phi) = √( x2 + z2)/y
• Similarly elbow angle at G is given by : tan (phi1)=√ (y2 +z2)/x

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
c. 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.

### 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:

Fig.3: Code equation for minimum thickness requirement calculation

Here,

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.

### 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”.
Fig.4: A typical Butt-Welded Elbow
• 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.
• Material standards as applicable to butt welded fittings are as follows:
ASTM A234:

This specification covers wrought carbon steel & alloy steel fittings of seamless and welded construction. Unless seamless or welded construction is specified in order, either may be furnished at the option of the supplier. All welded construction fittings as per this standard are supplied with 100% radiography. Under ASTM A234, several grades are available depending upon chemical composition. Selection would depend upon pipe material connected to these fittings.
Some of the grades available under this specification and corresponding connected pipe material specification are listed below:
ASTM A403:
This specification covers two general classes, WP & CR, of wrought austenitic stainless steel fittings of seamless and welded construction.
Class WP fittings are manufactured to the requirements of ASME B16.9 & ASME B16.28 and are subdivided into three subclasses as follows:
WP – SManufactured from seamless product by a seamless method of manufacture.
WP – W These fittings contain welds and all welds made by the fitting manufacturer including starting pipe weld if the pipe was welded with the addition of filler material are radiographed. However no radiography is done for the starting pipe weld if the pipe was welded without the addition of filler material.
WP-WX These fittings contain welds and all welds whether made by the fitting manufacturer or by the starting material manufacturer are radiographed.
Class CR fittings are manufactured to the requirements of MSS-SP-43 and do not require non-destructive examination.
Under ASTM A403 several grades are available depending upon chemical composition. Selection would depend upon pipe material connected to these fittings. Some of the grades available under this specification and corresponding connected pipe material specification are listed below:
ASTM A420:
• This specification covers wrought carbon steel and alloy steel fittings of seamless & welded construction intended for use at low temperatures. It covers four grades WPL6, WPL9, WPL3 & WPL8 depending upon chemical composition. Fittings WPL6 are impact tested at temp – 50° C, WPL9 at -75° C, WPL3 at -100° C and WPL8 at -195° C temperature.
• The allowable pressure ratings for fittings may be calculated as for straight seamless pipe in accordance with the rules established in the applicable section of ASME B31.3.
• The pipe wall thickness and material type shall be that with which the fittings have been ordered to be used, their identity on the fittings is in lieu of pressure rating markings.

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

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. An elbow is an engineering term and they are classified as 90 deg or 45 deg, short or long radius.
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. Bends are generally made or fabricated as per the need of the piping; however elbows are pre fabricated and standard, and are available off the shelf.
5. Bends are never sharp corners but elbows are. Pipe bending techniques have constraint as to how much material thinning can be allowed to safely contain the pressure of the fluid to be contained.  As elbows are pre fabricated, cast or butt welded, they can be sharp like right angles and return elbows which are 180 degrees.
6. Elbow is a standard fitting but bends are custom fabricated.
7. In bends as the pipe is bent and there is no welding involved, there is less pipe friction and flow is smoother. In elbows, the welding can create some friction.
8. All elbows are bends but all bends are not elbows.
9. Bend has a larger radius then elbows.
10. Generally the most basic difference is the radius of curvature. Elbows generally have radius of curvature between one to twice the diameter of the pipe.  Bends have a radius of curvature more than twice the diameter.

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.

### 90 degree short 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.
5. The short radius elbows are used where there is scarcity of space.

Credit: Wikimedia- 90 degree long radius elbow

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.

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.

Source: China Pipe Bend Manufacturer – Yaang Pipe Industry Co., Limited (www.epowermetals.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.)