Pipe elbows are used to be installed between two lengths of pipe or tube allowing a change of direction,usually these elbows distinguished by connection ends.
General standard of fittings
Many organizations such as ASME, ASTM, ISO, MSS, etc. have very well developed standards and specifications for buttwelded fittings.
ASTM A234/ASME SA234M
Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature ServiceASTM A420
Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature ServiceASTM A403
ASTM A403 Standard specification covers the standard for wrought austenitic stainless steel fittings for pressure piping applications.ASME B16.9
ASME B16.9 Standard covers overall dimensions, tolerances,ratings, testing, and markings for factory-made wrought buttwelding fittingsASME B16.28
ASME B16.28 Standard covers ratings, overall dimensions, testing, tolerances, and markings for wrought carbon and alloy steel buttwelding short radius elbows and returns.ANSI/ASME B16.25
ANSI/ASME B16.25 Standard covers the preparation of butt welding ends of piping components to be joined into a piping system by welding.MSS SP-97
This Standard Practice covers essential dimensions, finish, tolerances, testing, marking, material, and minimum strength requirements for 90 and 45 degree integrally reinforced forged branch outlet fittings of buttwelding, socket welding, and threaded types.
How to purchase pipe elbows?
Detecting the back arc of the elbow: Seamless elbow detection of the thickness of the back arc is an important task. Many large pipe elbow manufacturers or strict engineering inspection of the back arc is a must. It is related to the safety and stability of the pipeline operation.
Inspection end wall thickness
Mark
Inspection curved wall thickness
Measurement wall thicknessMeasurement wall thickness
PackingEveryone knows that both the pipeline and the seamless elbow are under pressure, that is, the pressure is very large when running. Under normal circumstances, the safety factor of the thickness of the seamless elbow designed and installed is about six times. For example, the 219*8 seamless elbow, the pipeline medium is ordinary water, the temperature is usually not higher than one hundred degrees Celsius, and the pressure required to blast such a seamless elbow is about 300 kg, that is, The pressure inside the pipeline needs to reach PN30, and the seamless elbow will be blasted, and the operating pressure of this elbow is probably about it. It is estimated that the maximum will not exceed PN6.4, which is generally around PN4.0, of course. With the corrosion of the pipeline, the seamless elbow will also be corroded to varying degrees. In order to ensure its safe operation, the necessity of overhaul is great.
The current process of making seamless elbows will lead to the phenomenon of back arc thinning. Under normal circumstances, the wall thickness of the mouth will be about two millimeters thinner than the back arc. The common thickness and pressure will not be thin even if the back arc is thinned. There are too many safety hazards, because the elbow has not been replaced until the elbow has a dangerous accident. But as a rigorous project, what is not the same, and the medium inside the pipeline is also responsible, not just water. There may be oil or other impurities, the temperature is high and the pressure is high, and the thickness of the back arc as the weak place determines the life of the seamless elbow. Therefore, the importance of detecting the back arc is naturally great. With a thickness gauge, read the thickness of a point at the elbow directly.
Detect the inner and outer diameters of the elbow: For example, the outer diameter dimension D of the elbow is detected: the data of the upper limit and the lower limit are referenced, and the actually measured outer diameter of the product is qualified between the upper and lower limits, and the unqualified product is outside the upper or lower limit range.
Detect the wall thickness of the elbow: use the thickness gauge to directly read the thickness of the thinnest part of the elbow.
Detect the center height of the elbow: first measure the length of the outer circle of the elbow. Using this length value /1.57, the value obtained by subtracting half of the diameter of the elbow is the center height of the elbow.
Detecting the weight of the elbow: The elbow is made of steel pipe. We only know the weight of the elbow when the elbow is cut, and the size of the elbow and the back arc of the elbow. The dimensions are basically the same. Let’s calculate the length of the back arc of the elbow: the diameter of the elbow is D, the radius of curvature is 1.5D, and the length of the back arc of the elbow is (1.5+0.5)*D*2*3.14/4 Simplification we can get, 1.5 times elbow back arc length L = D * 3.14. This is only an estimate. The value of the Chinese standard is slightly smaller than this value. After the length of the back arc is L, the weight of the steel pipe is calculated by the calculation formula of the steel pipe: (Da)*a*0.02466*L/1000, ( a is the wall thickness of the elbow), the unit of this weight is KG, so we can get the weight of the carbon steel elbow. If it is a stainless steel elbow, just replace 0.02466 with 0.02491. The calculated theoretical weight is then compared to the actual weight.
Radiographic inspection of elbows: Radiographic inspection detects volumetric defects of elbows, such as pores, slag inclusions, shrinkage cavities, and looseness.
Wide variety for all areas of application?
DIN
- St 35.8 I
- St 35.8 III
- 15 Mo 3
- 13 CrMo 4 4
- 10 CrMo 9 10
- St 35 N
- St 52.0
- St 52.4
EN
- P235GH-TC1
- P235GH-TC2
- 16Mo3
- 13CrMo4-5
- 10CrMo9-10
- X10CrMoVNb9-1
- P215NL
- P265NL
- L360NB
- L360NE
- P355N
- P355NL1
- P355NH
ASME
- WPB
- WPL6
- WPL3
- WPHY 52
- WP11
- WP22
- WP5
- WP9
- WP91
- WP92
Abrasion resistant Bend & elbow
Alumina ceramics have been developed and optimized for maximum wear resistance and corrosion resistance.
Pipe elbows FAQs:
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 of pipe elbows may be machined for butt welding , threaded , or socketed , so the elbows are consist of butt weld,thread elbow, socket elbow and other series.
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 typical elbow with elbow angle
ELL & ELLS
- 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.
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
Code equation for minimum thickness
requirement calculationAdd 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
A typical butt welded elbowButt 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.
3(D) x 2(NPS) x 25.4
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