A fitting is a weldable pipe fitting that allows for change of direction of flow, to branch off, reduce pipe size or attach auxiliary equipment. Pipe fitting is the occupation of installing or repairing piping or tubing systems that convey liquid, gas, and occasionally solid materials.
General standard of 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.
What is 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.
Pipe fittings and their applications
Pipe and pipe fittings go hand-in hand. Just as pipes are used for a variety of residential, public and industrial applications, so also the pipe fittings. No pipes can be connected without the use of proper fittings and flanges. Pipe fittings allow pipes to be installed and connected or joined where necessary and terminated in the right place.
Such as Oil and gas industries, Midstream, Shipbuilding, Power plants, Food plants, Pharmaceuticals, etc.
Pipe fittings include a wide range of products in various shapes, sizes and materials. With rapid developments in the field of industrial fittings and continuous research work in this industry, various new products are manufactured. Some fittings have certain special features so that they can be fabricated on different principles like hydraulics, pneumatic depending on the end usage.
Fittings include a comprehensive range of products depending on various applications in which they are applied.
Fittings are used wherever liquids, gases, chemicals and other fluids are created, processed, transported, or used.
There is no end to applications of pipe fittings so long there is no end to the applications of pipes . While the list of piping applications continues to expand, its strength, flexibility, very good flow rates and high chemical resistance are qualities which are uniquely suited for the movement or transfer of liquids, steam, solids and air from one point to another.
Pipe fittings come in many forms with the most common being threaded fittings, socket weld fittings and buttweld fittings. This blog will explore the advantages of all three types, but especially the advantages of buttweld fittings and their applications.
- Chemical
- Municipal
- Food, Beverage& Dairy
- Oil and Gas
- Power
- Instrumentation
- Pulp and Paper
- Semiconductor
- Marine & dredging
- Sanitation
- Piping Systems
- Irrigation
- Residential
- Road construction
- Ventilation etc
Pipe fittings are essential parts of pipelines as they allow for the following:
- A change in direction for the liquid flowing through the pipes
- Branching of the pipe to allow the liquid to flow in two separate directions
- A reduction in pipe diameter
- The attachment of auxiliary equipment
- The end of the pipeline
All the buttweld fittings supplied by Special Piping Materials are designed in accordance to ASME standards.
Advantages:
Buttweld fittings can withstand pressures and temperatures in very harsh environments. They are generally considered to be the most robust welding fixture, no matter what industry it is required for. However, they do take a considerable time to fit and a highly skilled installer is required to weld them correctly on site.
- Welded connection offers a more robust, a stronger and a more leak-proof piping connections.
- The nature of the continuous metal structure provides added strength to the overall piping system.
- The smooth inner surface and gradual directional changes provide a seamless flow, thus minimising pressure drops and turbulence inside the pipe.
- Provide the option of various different turn radiuses due to the manufacture of Short Radius fittings, Long Radius fittings and 3R Elbows.
- They are cost effective compared to the counterpart fittings in the threaded or socket weld varieties.
- They have a long service life and are cost effective to purchase and deploy.
- Buttweld fittings can withstand corrosion and erosion more effectively than its socket weld and threaded equivalents.
- A welded system uses comparatively less space that the other alternatives.
Recommended pipe fittings
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Abrasion resistant Pipe fittings
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Fittings FAQs:
These fittings are the most common type of welded pipe fitting and are specified by nominal pipe size 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.
Benefits of welded fittings
The allowable pressure ratings for fittings designed in accordance with the standard ASME B 16.9–1993 may be calculated as for straight seamless pipe in accordance with the rules established in the applicable section of the ASME B 31 codes for pressure piping.
- are strong and leak-proof
- minimize the pressure drops and the turbolence along the pipeline
- have a long service life
How are pipe fittings measured ?
- (Fittings are also defined by their material grade and whether they are welded or seamless.)
- Diameter refers to outside diameter of a pipe or fitting.
- The North American standard is known as Nominal Pipe Size (NPS). The International Standard is known as Diameter Nominal (DN). Pipes and fittings are actually made in similar sizes around the world: they are just labeled differently.
- From ½ in to 12 inch “Nominal Pipe Size”, outside diameters are slightly larger than indicated size; inside diameters get smaller as schedules grow.
- From 14 in and larger “Nominal Pipe Size”, outside diameters are exactly as indicated size; inside diameters get smaller as schedules grow.
- As with other North American standards (inch, foot, yard, mile, …), many pipe standards (diameters up to 12 inch and wall thickness) are based on historical precedents (a toolmaker’s dies during US Civil War) rather than a “scientific” method.
Why are fittings sometimes thicker and heavier than pipes to which they are connected ?
Fittings are sometimes thicker than their connecting pipes to meet performance requirements or due to manufacturing reasons.
- Due to fitting geometry, stress is very different when compared to a pipe.
- Using extra material is often necessary to compensate for such additional stress, especially for tees and tight curve elbows.
- Fitting manufacturers may not always stock plates or pipes for all metal grades or sizes.
- When responding to an order, manufacturers always use the right metal or alloy, but sometimes made with next-higher available plate or pipe size while still respecting specified inside diameters.
What does “schedule” mean for pipe fittings ?
As the main function of the pipes is to carry fluid under pressure therefore their internal diameter is their critical dimension. This critical dimension is referred to as the nominal bore (NB). Obviously, for pipes containing pressurised fluids the wall thickness, and by implication the pipe’s strength, is important. Wall thickness is expressed in “schedules“, referred to as pipe schedules. The pipe schedule is abbreviated as SCH.
Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures.
- Schedule, often shortened as sch, is a North American standard that refers to wall thickness of a pipe or pipe fitting. Higher schedules mean thicker walls that can resist higher pressures.
- Pipe standards define these wall thicknesses: SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS and XXS. (S following a number is for stainless steel. Sizes without an S are for carbon steel.)
- Higher schedules are heavier, require more material and are therefore more costly to make and install.
What does 45 SR or 90 LR mean for pipe fittings ?
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.
- 45 and 90 refer to angles for changing direction of pipe flows: 45 degrees or 90 degrees. Most elbows are 45˚ or 90˚.
- SR means Short Radius; LR means Long Radius. Centerline radius of long radius (LR) elbows is smoother than of short radius (SR).
- In SR fittings, radius equals nominal diameter size. A 6 inch pipe will have a 6 inch radius center-to-end, giving it a sharp curve.
- In LR fittings, radius equals 1.5x nominal diameter size. A 6 inch pipe will have a 9 inch centerline radius, for a smoother curve than SR.
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.
What is the difference between a 3R and a 3D elbow?
There is no difference between 3R and 3D.
- Both have a centerline radius of three times the nominal diameter size.
- Both have a smoother curve than an SR or LR.
- (In fittings, 3D does not refer to modeling software or screens.)
What is the difference between concentric and eccentric reducers ?
A reducer is the component in a pipeline that reduces the pipe size from a larger to a smaller bore (inner diameter).
- Concentric reducer is symmetrical both ends are aligned along the center.
- Eccentric reducer is not symmetrical ends are off center of one another.
What is a lateral pipe fitting ?
A lateral separates one line into two; the second line branches at a 45˚ angle.
The WYE have two branch pipes at a 45 degree angle between them,and the two branch pipes are symmetrical to the centerline of the inflow pipe which means the two outflow direction are both at 22.5 degree to the inflow direction.
What is a seamless butt weld fitting?
A seamless butt weld pipe fitting is made directly from a section of seamless pipe material, by applying heat and pressure to transform pipe directly into an elbow or other shape.
A seamless fitting has no welded parts by itself, a characteristic demanded in some critical applications.
By comparison, a regular butt weld fitting has one, two or more welds, depending on dimension, shape and manufacturing method.
No weld means less risk of weld yield and porosities.
What is PVF?
PVF means Pipe, Valve and Fittings, and is widely used as short-hand to describe this industry.
PVFs can be made in a variety of metals or plastics.
Manufacturers typically specialize in special types of materials; distributors can carry narrow or very broad product lines.
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°
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.
End connections
There are four different type of connections that are used for fittings:
- Butt Weld Fittings – Probably the most common type of fitting. They are easily manufactured and are easily installed. Butt weld fittings can be connected directly to each other. This is called fitting make up.
- Flanged Fittings – Flanged fittings are piping components where the flange is an integral component of the fitting. These are most often used in water treatment applications or lined piping where welding would be destructive to the liner.
- Socket Weld Fittings – These fittings have a socket weld connection on each end. They might be used for smaller diameter piping. These fittings utilize a single fillet weld to join the piping with the fitting.
- Threaded Fittings – Threaded fittings are generally four inches and smaller. The reason for this size constraint is the pipe end needs to be threaded with a male type connection and die sizes are unobtainable in the larger diameters.
Fitting Weights
ASME buttweld fitting specifications do not specify weights for fittings.
Weights quoted in the tables on this page are based on manufacturers information and should be considered as approximate and provided as a guide only (fitting weights can vary considerably between manufacturers due to differences in construction).
Three groups:
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.
