What is a Butt Weld (Buttweld) Fitting?

A buttweld fitting is a weldable pipe fitting that allows for change of direction of flow, to branch off, reduce pipe size or attach auxiliary equipment. Forged Steel buttweld  are manufactured in accordance with ANSI / ASME B16.9.
There are many different types of fittings and they are the same in all sizes and schedules as the pipe.
Fittings are divided into three groups:
• Buttweld (BW) fittings whose dimensions, dimensional tolerances et cetera are defined in the ASME B16.9 standards. Light-weight corrosion resistant fittings are made to MSS SP43.
• Socket Weld (SW) fittings Class 3000, 6000, 9000 are defined in the ASME B16.11 standards.
• Threaded (THD), screwed fittings Class 2000, 3000, 6000 are defined in the ASME B16.11 standards.
Butt weld fittings are available as elbows, tees, caps, reduces and out lets (olets). These fittings are the most common type of welded pipe fitting and are specified by  and pipe schedule. Buttweld fittings use seamless or welded pipe as the starting material and are forged (through multiple process) to get he shape of elbows, tees and reducers etc. Just as the pipe is sold from Schedule 10 to Schedule 160, butt weld pipe fittings are sold the same way. Welded butt weld fittings are more common in stainless steel due to cost advantage. Sch 10 fittings are also more common in stainless steel butt weld fitting.
Common material for butt weld fittings are A234 WPB (A & C also available), High Yield Carbon Steel, Stainless Steel 304 and 316 and Nickel Alloys.
Buttweld pipe fittings comprises of long radius , concentric reducer, eccentric reducers and Tees.They are an important part of industrial piping system to change direction, branch off or to mechanically join equipment to the system. Buttweld fittings are sold in nominal pipe sizes with specified pipe schedule. BW fitting’s dimensions and tolerances are defined as per ASME standard B16.9.
Butt Weld fittings are also called Welded Pipe fittings. These welded fittings in carbon steel and stainless steel offer many advantages compared to threaded and socketweld fittings. The later are only available up to 4-inch nominal size whereas butt weld fittings are available in sizes from ½” to 72”. Some of the benefits of Buttweld fittings are;

Types of Butt Weld Pipe Fittings
1. Elbow 90° long radius 2. Elbow 45° 3. Elbow 90° short radius 4.Elbow 180° long radius 5. Elbow 180° short radius 6.  straight 7.Tee reducing 8. Reducer concentric 9. Reducer eccentric 10. 11. Lap joint 

Welded pipe fittings in carbon steel and stainless steel are the joining components that make possible the assembly of valves, pipes and equipment onto the piping system. Welded fittings compliment pipe flanges in any piping system and allows;
  • Change direction of flow in a piping system
  • Connect or joint pipes and equipment
  • Provide branches, access and takeoffs for auxiliary equipment
A common example using welded pipe fitting is a pipe reduced by concentric reducer, welded to a and connected to an equipment. Figure below represent complete collection of butt welded pipe fitting

Applications of Buttweld Fittings
A piping system using buttweld fittings has many inherent advantages over other forms.
  • Welding a fitting to the pipe means it is permanently leakproof
  • The continuous metal structure formed between pipe and fitting adds strength to the system
  • Smooth inner surface and gradual directional changes reduce pressure losses and turbulence and minimize the action of corrosion and erosion
  • A welded system utilizes a minimum of space

Bevelled Ends
The ends of all buttweld fittings are bevelled, exceeding wall thickness 4 mm for austenitic stainless steel, or 5 mm for ferritic stainless steel. The shape of the bevel depending upon the actual wall thickness. This bevelled ends are needed to be able to make a “Butt weld”.
ASME B16.25 covers the preparation of buttwelding ends of piping components to be joined into a piping system by welding. It includes requirements for welding bevels, for external and internal shaping of heavy-wall components, and for preparation of internal ends (including dimensions and dimensional tolerances). These weld edge preparation requirements are also incorporated into the ASME standards (e.g., B16.9, B16.5, B16.34).

Material and Performance
The most common materials used in fittings produced is carbon steel, stainless steel, cast iron, aluminium, copper, glass, rubber, the various types of plastics, etc..
In addition, fittings, like pipes, for specific purposes sometimes internally equipped with layers of materials of a completely different quality as the fitting themselves, which are “lined fittings”.
The material of a fitting is basically set during the choice of the pipe, in most cases, a fitting is of the same material as the pipe.
Buttweld Pipe Fitting Specification & Standards
Welded pipe fittings are made as per ASME spec B16.9. ASME B16.9 covers factory made wrought steel butwelding fittings in sizes 1/2″ to 48″. This standard however does not cover low pressure corrosion resistant buttwelding fittings. See MSS SP-43, Wrought Stainless Steel Butt-Welding Fittings.
Common Materials for Welded Pipe Fittings
Carbon Steel Welded Fitting:
A234 WPB is the most common material used for carbon steel butt welded fittings.
ASTM A234 WPB is the Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service.
Specifications
  • ASTM: A234 WPB
  • ASME: B16.9, B.11
  • NACE: MRO175
  • MSS: SP-83, SP-95
Chemical Composition%
GradeCMnPSSiCrMoNiCuOthers
maxmax
WPB0.30.29-1.060.050.0580.10.40.150.40.4V 0.08
(1,2,3,4,5)maxminmaxmaxmaxmaxmax
  1. Fittings made from bar or plate may have 0.35 max carbon.
  2. Fittings made from forgings may have 0.35 max Carbon and 0.35 max Silicon with no min.
  3. For each reduction of 0.01% below the specified Carbon maximum, an increase of 0.06% Manganese above the specified maximum will be permitted, up to a maximum of 1.35%.
  4. The sum of Copper, Nickel, Niobium, and Molybdenum shall not exceed 1.00%.
  5. The sum of Niobium and Molybdenum shall not exceed 0.32%.
Stainless Steel Butt Weld Fittings:
Stainless buttweld fittings are available in 316 and 304 grades.
304/304L (UNS S30400/S30403)              
Chemical Composition%
CCrMnNiPSSi
MAXMAXMAXMAXMAX
0.03518.0- 20.02.008.0-13.00.0450.0301.00
Tensile Requirements                                 
Tensile Strength:  (KSI) = 60
Yield Strength:  (KSI) = 35
(KSI converts to MPA {Megapascals} by multiplying by 6.895)
316/316L (UNS S31600/S31603)              
Chemical Composition%
CCrMnMoNiPSSi
MAXMAXMaxMAXMAX
0.03516.0- 18.02.002.0-3.010.0-14.00.0450.0301.00
Tensile Requirements                                 
Tensile Strength:  (KSI) = 70
Yield Strength:  (KSI) = 25
(KSI converts to MPA {Megapascals} by multiplying by 6.895)
How a Butt Weld Fitting is Made?
A butt weld pipe fitting is made by the process of hot forming that includes bending and forming to shape. The starting material of butt weld fitting is a pipe that is cut to length, heated and molded into specific shapes by means of dies. Heat treatment is also done to remove residual stresses and obtain desired mechanical properties. Read the link here to get more in depth detail of butt weld fitting manufacturing.

Benefits of Butt Weld Pipe Fittings
Welded connection offers more robust connection
  • Continuous metal structure adds to the strength of the piping system
  • Buttweld fittings with matching pipe schedules, offers seamless flow inside the pipe. A full penetration weld and properly fitted LR 90 Elbow, Reducer, Concentric reducer etc. offers gradual transition via welded pipe fitting.
  • Option of various turn radius using Short Radius (SR), Long Radius (LR) or 3R Elbows
  • Cost effective compared to their expensive threaded or socket weld counter parts.
  • Stainless Steel Welded Fittings are also available in SCH 10, allowing a more thinner wall option.
  • Stainless Steel Butt Weld Fittings are more common in SCH 10 and SCH 40 configuration.
All butt weld fittings have beveled ends as per ASME B16.25 standard. This helps create full penetration weld without any extra preparation needed for the butt weld fitting.
Butt weld pipe fittings are most commonly available in carbon steel, stainless steel, nickel alloy, aluminum and high yield material. High yield butt weld carbon  fittings are available in A234-WPB, A234-WPC, A420-WPL6, Y-52, Y-60, Y-65, Y-70.  All WPL6 pipe fittings are annealed and are NACE MR0157 and NACE MR0103 compatible.

Q&A
We handle hundreds of requests every day. Some of the common misconceptions are addressed in Q&A below;
Customer call butt weld fittings in A105: Most common carbon steel buttweld fitting material is A234WPB. It is equivalent to A105 flanges, however there is no such thing as A105 or  butt weld fitting
Customer request “Normalized” butt weld fittings: This is also a misconception since flanges are available in A105 and A105 N, where N stands for normalized. However, there is no such thing as A234WPBN. Some manufactures normalize their butt weld fittings as a standard procedure and such request require checking individual material test certificates to verify if normalized heat treating process was done. Customer needing “normalized” butt weld fittings should request WPL6 fittings which are high yield and are normalized as a standard procedure
Customer forget to mention pipe schedule: Buttweld fittings are sold as per pipe size but pipe schedule must be specified to match the ID of the fitting to the ID of the pipe. If no schedule is mentioned, we will assume a standard wall is requested.
Differentiate between SCH 40 & True Schedule 40: Pipe fittings 12 inch or larger require specifying if fitting is standard wall (most commonly referred to sch 40) or a true schedule 40 is required. This is needed since schedule 40 do NOT correspond to standard wall for pipe sizes 12” and bigger. A true sch 40 will be thicker than standard wall for pipe fittings 12” or bigger.
Differentiate between SCH 80 & True Schedule 80: For pipe sizes 10 in and above, sch 80 do NOT correspond to XH. Customer must specify if they want SCH 80 or XH wall.
Stainless Steel buttweld pipe fittings are available in schedule 10s: Customer should specify if they need standard wall (sch 40s) or a thinner wall sch 10s stainless steel butt weld fitting. See pipe chart to clarify how the wall thickness for stainless steel pipes correlated to different pipe schedules.
Customer forget to mention welded or seamless butt weld fitting: Butt weld fittings are available in both welded and seamless configuration. A seamless butt weld carbon steel or stainless steel fitting is made of seamless pipe and is generally more expenses. Seamless pipe fitting is NOT common in sizes bigger than 12”. Welded pipe fittings are made of ERW welded carbon steel or stainless steel pipe. They are available in sizes ½” to 72” and are more affordable than seamless fittings.
What does Short Radius (SR) or Long Radius (LR) means?
You will often hear SR45 elbow or LR45 elbow. The 45 or 90 refers to the angle of the bend for buttweld fitting to change the direction of flow. A long radius elbow (LR 90 Elbow or LR 45 elbow) will have a pipe bend that will be 1.5 times the size of the pipe. So, a 6 inch LR 90 has bending radius that is 1.5 x nominal pipe size. A short radius elbow (SR45 or SR90) has pipe bend that is equal to the size of fitting so a 6” SR 45 has bending radius that is 6” nominal pipe size.
What is a 3R or 3D elbow pipe fitting?
First, the term 3R or 3D are used synonymously. A 3R butt weld elbow has bending radius that is 3 times the nominal pipe size. A 3R elbow is smoother than SR or LR fitting.
Welded Pipe Reducers
Butt weld fittings are available in concentric reducer and  to reduce the flow from one size of pipe to another. A concentric reducer butt weld fitting is symmetrical: both ends are aligned along the center.
An eccentric reducer butt weld fitting is not symmetrical: ends are off center of one another.

Butt Weld Fitting Collection
LR 90 Elbow: Fittings that change direction in a piping system are called elbows. The directional change is given in degree such as 45 or 90. Long radius 90 degree elbow has the center line of elbow at 1.5 x NPS from eblow end. 3R elbow has center line at 3 x NPS from elbow end.
LR 45 Elbow: Long radius 45 degree elbow changes the direction by 45 degrees.
SR90 Elbow:  is same as LR90 except for the measurement between end of elbow to center line is 1 x NPS.SR90 Elbow
LR 180 degree Bend: Long Radius 180 degree return bend allows complete reversal of flow. The distance between end of elbow and center line is 3 x NPS.return bend 180 deg LR
SR 180 degree Bend: Short Radius 180 degree return bend allows complete reversal of flow but in a much tighter turn. The distance between end of elbow and center line is 1 x NPS.
Tee: Butt weld pipe Tee allows a 90 degree branch off from a running pipe.This allows for connecting auxiliary equipment to a pipe. A tee is welded on both side to the pipe, leaving the branch open for branch off.
Reducing Tee: Butt weld reducing tee has a branch that is smaller than main run. This allows for branching off to a smaller pipe of equipment from the main run. Reducing Tee
Concentric Reducer: A concentric Reducer is also called welded concentric coupling. It allows from connecting a large pipe to a smaller pipe by means of welding. A concentric reducer allows welded connection between two pipes with the same center line.
Eccentric Reducer: An eccentric reducer is also called welded eccentric coupling. It allows for welding a large pipe to a smaller pipe with an offset center line. The offset of the center line in an eccentric reducer is; Offset = 1/2 x (Largest ID – Smallest ID)
Weldolet: A weldolet, also called welding outlet, is a way of connecting a welded connection that is contoured at the bottom to match the contour of the pipe. So one end of welding outlet is welded on the pipe, whereas the other end is open to be welded to any other pipe or equipment. A welding outlet requires mentioning the size of out let and the “Run Size” of pipe so the contour can match the contour of the pipe. The size of welding outlet will always be smaller than run size such as 1/2″ welding outlet can be used on pipe (run size) 1/2″ and bigger.
Welded Stub End: Stub ends are used with lap joint flange to welded onto the pipe.

Long and Short Radius
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.
Pipe ebows 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.
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.
Here below, for example, you will find the<br />center to face distance of NPS 2 elbows<br />(the A distance on the image)
1. 90°-LR : = 1½ x 2(NPS) x 25.4 A=76.2 mm
2. 180°-LR : = 2 times the 90° LR elbow A=152.4 mm
3. 90°-SR : = 2(NPS) x 25.4 A=50.8 mm
4. 180°-SR : = 2 times the 90° SR elbow A=101.6 mm
SR (Short Radius) Elbows: These elbows have a Center-to-Face dimension of 1.0 X diameter. They are typically used in tight areas where clearance is the main issue.
LR (Long Radius) Elbows: These elbows have a Center-to-Face dimension of 1.5 X diameter. They are the most common type of elbow and used when space is available and flow is more critical.
Reducing Elbow: A reducing elbow is a type of fitting which is used to join two pieces of pipe of different sizes. The reducing elbow is so called because it looks like a reducing piece and elbow combined into one. Reducing elbows have different sized openings on each end and hence they can connect two different sized pipes. They are available in different materials, sizes, finishes and colors.
45° Pipe Elbow: 45° Pipe Elbow is also known as “45 bends or 45 ells”. The 45° pipe elbow is used to connect tubes at a 45° pipe angle. As the name suggests, this is a pipe fitting device which is bent in such a way to produce 45° change in the direction of flow of the fluid/gas in the pipe.
Like a 90° elbow, the 45° pipe elbow also attaches readily to pipes of various materials like plastic, copper, cast iron, steel, lead, rubber etc. They are typically made as LR (Long Radius) elbows. These types of elbows are available in various sizes (in mm or inches). They are available with different male to female BSP thread connections. Providing a wide choice of colors, these 45° elbows can be manufactured to meet different specifications, in terms of size and diameter.
Male Pipe Elbows & Female Pipe Elbows: Male pipe elbows and female pipe elbows are popular tube fittings which provide an angled change in the direction of a tubing run. While a male pipe elbow is used to connect fractional tube to female tapered pipe thread, a female elbow is used to connect fractional tube to male NPT thread. These types of tube fittings like male elbows and female elbows have been specifically designed for use on instrumentation, process and control systems and equipment employed in chemical, petroleum, fluid power, electronic and pulp and paper plants.
The most applied version is the 90° long radius and the 45° elbow, while the 90° short radius elbow is applied if there is too little space. The function of a 180° elbow is to change direction of flow through 180°. Both, the LR and the SR types have a center to center dimension double the matching 90° elbows. These fittings will generally be used in furnesses or other heating or cooling units.
Dimensions, dimensional tolerances and more images, can be found in the main Menu “Fittings”.
In addition to the defined elbows, there is the Reducing Elbow, which is a elbow with various diameters on the ends. Because this elbow, for many suppliers it is not a standard item, and thus probably a high price with a long delivery time, the use of a “normal” elbow with a separate reducer is an option if the situation allows.
Reducing elbow 90°: Other degrees elbows can be machined from a standard elbow. Longer radius type, the center to face dimension e.g. is three times the nominal size (3D), even is available.

Butt weld fittings

Butt weld  get their name from the method for which they attached to a piping system. Each end of a butt weld fitting is beveled, and it is attached by butting the fitting up to the adjoining pipe and welding along the bevel. This connection is both stronger and smoother than threaded or socket weld connections, making butt weld the preferred product for critical applications.
 is a full-line distributor of butt weld fittings, offering carbon steel, stainless steel, and exotic alloys. With sizes ranging from 1/4” to 48″,  can provide the butt weld fittings required for virturally any piping project.
Large quantites, custom sizes, and special alloys ( 20, Monel, Hastelloy, Inconel, Titanium, etc) may be subject to a longer lead time for delivery.
Size Range:1/4″ to 48″ Diameter
Types:90, 45, 180, Tee, Cross, Ecc Reducer, Conc Reducer, Cap, Stub End, Lateral, Swage Nipples, Bull Plugs, Pipe Nipples
Schedules:5, 10, 40 (STD), TRUE 40, 80 (XH), TRUE 80, 100, 120, 160, XXH
Carbon Steel:A234 WPB, Y52, Y60, Y65, Y70
Stainless Steel:304, 310, 316, 321, 347
Exotic Alloys:A20, C276, Duplex 2205, AL6XN, A200, A600, Monel, Inconel, Incoloy
ORDERING INFORMATION
There are some need-to-know details when purchasing butt weld fittings, such as: diameter, schedule, material, the shape/type of the fitting, and whether it is seamless or welded construction (A234 WPB carbon steel butt weld fittings come seamless below 24”).
WALL THICKNESS
The schedule of the butt weld fitting must match the schedule of the butt weld fittings it is being welded to. These schedules are outlined in the butt weld fittings chart section of the website.
MATERIAL AND CONSTRUCTION
The following offers an in-depth view of the butt weld fitting material grades sold by Sunny Steel Supply. Each link below will provide the chemical composition, manufacturing specifications, yield and tensile strength, as well as other specific product and grade information.
CARBON STEEL BUTT WELD FITTINGS
 A234 – Wrought Carbon and Alloy Steel Butt Weld Fittings : This specification covers wrought carbon steel and alloy steel butt weld fittings of seamless and welded construction. This is the most common material for carbon steel butt weld fittings (specifically grade WPB) and is seamless up to 24”, where diameters of 24” or larger may come seamless or welded. These butt weld fittings are for use in pressure piping and in pressure vessel fabrication for service at moderate and elevated temperatures.
ASTM A860: This specification covers wrought high-strength ferritic steel butt weld fittings of seamless and electric fusion-welded construction covered by the latest revisions of ASME B16.9 and MSS-SP-75. These butt weld fittings are for use in high-pressure gas and oil transmission and distribution systems.
STAINLESS STEEL BUTT WELD FITTINGS
A403 – Seamless and Welded Stainless Butt Weld Fittings: This specification covers the standard for seamless and welded wrought austenitic stainless steel butt weld fittings for pressure piping applications.
SPECIAL ALLOY STEEL BUTT WELD FITTINGS
Special alloy butt weld fittings are used for applications that require more demanding performance, such as extreme temperature and corrosive resistance. Each of the following exotic alloys provides unique attributes for such engineered applications. Applications for these alloys include, but are not limited to: chemical processing, chemical storage, pollution control, waste treatment, food processing, and pharmaceutical equipment.

TYPES OF BUTT WELD FITTINGS
TEES
Tees are butt weld fittings used to combine or divide process flow, and Reducing Tees additionally allow for butt weld fittings size change. The run outlets of the tee are the two in-line outlets, and the branch is the third outlet. The branch outlet is the reducing outlet in a reducing tee.


An elbow is a butt weld fitting is used to change the direction of flow in a piping system, usually at the 90° or 45° angle. Like a reducing tee, reducing elbows also exist to simultaneously change flow direction and reduce flow diameter. 90 degree elbows are also available in both short radius and long radius patterns, whereas 45 degree elbows are only available as long radius.
LONG RADIUS (LR) VS SHORT RADIUS (SR) ELBOWS
A long radius butt weld elbow has a radius of curvature (Identified as “A” in the above drawing) is 1.5 times the nominal diameter, and a short radius butt weld elbow has a curvature that is 1.0 times the nominal diameter of the butt weld fitting. Long radius butt weld elbows give less frictional resistance to the fluid than the short radius butt weld elbows. Short radius butt weld elbows are generally cheaper and can be used where space is a concern, but they also create a greater pressure drop than long radius butt weld elbows.
Bend vs Elbow
There is often confusion around  and elbows.  are generally made or fabricated as per the need of the piping design, whereas elbows are manufactured in mass quantities, conform to industry standard size specifications, and available off the shelf. Butt Weld Fitting  techniques also face constraints regarding material thinning, and if not done properly, there can be concerns regarding the pressure integrity of the line being maintained. Elbows are most commonly used for SR and LR , but when the curvature exceeds 3R,  are most commonly utilized.

Reducers
Reducers are butt weld fittings used to facilitate a reduce the flow diameter in a piping system. Concentric reducers are most commonly used, as they create less friction for the fluid flow, however, eccentric reducers are utilized when space or alignment is a concern.

Cross
Crosses are a 4 way butt weld fitting, with 1 inlet and 3 outlets or vice versa. These are sometimes referred to as 4-way tees.

Caps
Caps are butt weld fittings used to terminate the flow, welding to the end of a butt weld fitting or pipe.

A useful detailed literature for piping engineers about Piping Elbows and Bends

Piping Elbow and Piping bend are not the same, even though sometimes these two terms are interchangeably used.

Piping Elbows and Bends are very important  fitting which are used very frequently for changing direction in piping system. Piping Elbow and Piping bend are not the same, even though sometimes these two terms are interchangeably used. A BEND is simply a generic term in piping for an “offset” – a change in direction of the piping. 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 machine (hot  and cold ) on site and suited for a specific need. Use of bends are economic as it reduces number of expensive fittings.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.

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

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.

Example figure for elbow angle calculation
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
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:

Code equation for minimum thickness requirement calculation
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  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.
 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”.

A typical Butt-Welded Elbow
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  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:
:
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.

Seamless steel pipe >>

Seamless steel pipe >>
Seamless steel pipe is alos called CDS pipes (Cold drawn seamless pipe).

Pipe fitting >>

Pipe fitting >>
Pipe fitting is work that involves the installation or repair of pipes or tubes. Pipes and tubes are necessary for a wide range of reasons.

Flanges General >>

Flanges General >>
A flange is a method of connecting pipes, valves, pumps and other equipment to form a piping system.

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