Pipe elbows

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.

By default, there are 5 opportunities, the 45°, 90° and 180° elbows, all three in the "long radius" version, and in addition the 90° and 180° elbows both in the "short radius" version.

How to purchase pipe elbows?

How to distinguish between pipe elbow and pipe bend?

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.

Everyone 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.

A324 WP22 elbow
Inspection
A324 WP22 elbow
Mark
Packing
Packing
Bending
Inspection
 Measurement wall thickness
Measurement wall thickness
Protect the end of the bending
Protect the end of the bending

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.

Abrasion resistant Bend & elbow

Abrasion resistant piping systems are widely used at coal-fired power plants for a variety of purposes, including the conveyance of coal ash slurry to nearby settling ponds, the transfer of limestone slurry to absorber spray towers for removal of sulfur dioxide (SO2) and hydrogen chloride (HCl) from flue gases and for transporting away the calcium sulfate by-product of the flue gas desulfurization process.

Features of Alumina Ceramic lined elbow:
Alumina is a cost effective and widely used material in the family of engineered ceramics.

Alumina ceramics have been developed and optimized for maximum wear resistance and corrosion resistance.

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.

Tensile Requirements WPB WPC, WP11CL2 WP11CL1  WP11CL3
Tensile Strength, min, ksi[MPa] 60-85 70-95 60-85  75-100
(0.2% offset or 0.5% extension-under-load) [415-585] [485-655] [415-585]  [520-690]
Yield Strength, min, ksi[MPa] 32 40 30 45
[240] [275] [205] [310]

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.

Steel No. Type Chemical composition
C Si S P Mn Cr Ni Mo Other ób ós δ5 HB
WPL6 0.3 0.15-0.3 0.04 0.035 0.6-1.35 0.3 0.4 0.12 Cb:0.02;V:0.08 415-585 240 22
WPL9 0.2 0.03 0.03 0.4-1.06 1.6-2.24 435-610 315 20
WPL3 0.2 0.13-0.37 0.05 0.05 0.31-0.64 3.2-3.8 450-620 240 22
WPL8 0.13 0.13-0.37 0.03 0.03 0.9 8.4-9.6 690-865 515 16

DOWNLOAD STANDARD

Even welding and smooth weld line, can be substitute for seamless tube after drawing and cold rolling.

ASME B16.9

This Standard covers overall dimensions, tolerances, ratings, testing, and markings for wrought factory-made buttwelding fittings in sizes NPS 1 ⁄ 2 through 48 (DN 15 through 1200).

Fittings may be made to special dimensions, sizes, shapes, and tolerances by agreement between the manufacturer and the purchaser.

ASTM A234/ SA234M

ASTM A234/ SA234M Standard specification for pipe fittings of wrought carbon steel and alloy steel for moderate and high temperature service.

These fittings are for use in pressure piping and in pressure vessel fabrication for service at moderate and elevated temperatures.

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

Elbows are design features as below

ELL & ELLS

A typical elbow with elbow angle
A typical elbow with elbow angle

” 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:

Code equation for minimum thickness requirement calculation
Code equation for minimum thickness
requirement calculation

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:

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.

A typical butt welded elbow
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.

3D elbows as an example, are calculated with:
3(D) x 2(NPS) x 25.4

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.

The material is selected accoding to the application use such as high temperature use,sanitary fitting,regular industrial use etc.

  • Carbon steel: ASTM A234 WPB, WPC, ASTM A420 WPL1, WPL3, WPL6, WPHY-42/46/52/56/60/65/70
  • Stainless steel: ASTM A403 WP304/304L, WP316/316/L, WP321, WP347 and WPS31254
  • Alloy steel: ASTM A234 WP1/WP12/WP11/WP22/WP5/WP7/WP9/WP91
  • Abrasion resistant material: Ceramic lined, Ceramic tile lined , Bi-metal clad pipe,
  • Manufacturing standards: ANSI, ISO, JIS and DIN.

Common type of Butt weld pipe fittings

A common example using welded pipe fitting is a pipe reduced by concentric reducer, welded to a weld neck flange and connected to an equipment. Figure below represent complete collection of butt welded pipe fitting



Fitting specification, Standard and identification

There are different varieties of pipe fittings made of various materials and available in various shapes and sizes.



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