FAQ related to pipe fittings, what are pipe fittings?
Let us get to know more about pipe fittings and flanges by answering some simple questions:
Q.1 What exactly do you mean by pipe
A. Pipe fittings are used to connect pipes. There are different varieties of pipe fittings made of various materials and available in various shapes and sizes. Pipe adapters, couplings, elbows, tees, sleeves, flanges, bulkhead fittings, reducers, valves etc. are all different types of pipe fittings.
Q.2 How are pipe fittings identified?
A. Pipe fittings are identified by their material of construction, inner and outer diameter of the pipe, and the type of fitting whether threaded or slip, male or female.
Q.3 What is an elbow?
A. The elbow is a short length of pipe having a 90-degree bend. Elbow allows pipes to be connected securely at both ends, providing a clean turn.
Q.4 What is the outside diameter (OD) of a 1″ fitting?
A. The outside diameter (OD) of a fitting will vary from manufacturer to manufacturer and it represents the minimum wall thickness requirements for a given size.
Q.5 Are pipe fittings having a visible line
in them, are cracked?
A. No. The noticeable line is not a crack. This you can test by trying to open the crack. If you are unable to open it up by pulling on the part then that is knit-line which is an intrinsic part of the injection-molding process. A knit-line will not impact the integrity of the pipe fitting.
Q.6 How are pipe fittings organized by male
and female connectors?
A. There are four ways to consider for this:
- Male threaded: Threads on the outside. They are made to screw into the inside of a larger diameter pipe end with internal threading.
- Female threaded: Threads are on the inside. They are made to receive male threaded pipe fittings.
- Male slip fit: There are no threads. They are made to slip into a slightly larger female sleeve.
- Female slip fit: There are no threads. They are made to receive a narrower male slip fit.
Q.7 What should I consider for buying pipe fittings?
A. Material, Size, Temperature and Pressure Ratings, Durability, Standards etc.
Q.8 Is it acceptable to change the design of a plastic fitting?
A. No. Fittings are manufactured as per stringent ASTM dimensional requirements.
Q.9 What are threaded fittings?
A. Most commonly used in steel fittings. Uses pipe dope or PTFE tape on the threads which when joined will prevent leaks and corrosion. The fitting is female if the threads are on the interior. The fitting is male, if the threads are on the exterior.
Q.10 What is a flange?
A. A flange is usually in the shape of a plate or ring which forms a rim at the end of a pipe when fastened to the pipe.
Q.11 What is a standard used in pipe fittings?
A. Standards are certain authentication given in reference to manufacture and installation of the product . Some common standards are BSP, NPT, ANSI, ASME etc.
What is a butt weld pipe fitting ?
A butt weld pipe fitting is designed to be welded on site at its end(s) to connect pipe(s) together and allow change in direction or pipe diameter, or branching or ending.
This fitting then becomes part of a system for transporting fluids (oil, gas, steam, chemicals, …) in a safe and efficient manner, over short or long distances.
Other types of fittings can be threaded or socket welded.
What are advantages of butt welding over flanges ?
- Flanges connect pipes by bolting them together, whereas butt weld fittings connect pipes by welding them together.
- Depending on size, butt weld fittings require 10% to 75% less material than a flanged connection, which means lower material cost and lower weight.
- Welded construction permits greater freedom in designing a layout; this system uses less space, is more compact, and has greater strength.
- Butt weld fittings provide optimum flow characteristics, without pockets or sharp corners, creating less frictional resistance, no pressure loss, less turbulence, …
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.
In what industries are pipe fittings used ?
Fittings are used wherever liquids, gases, chemicals and other fluids are created, processed, transported, or used. Range of industries is very wide, as shown below:
- Energy related. Oil and gas industries, including upstream (exploration and production), midstream (transportation by ships, pipeline, rail, trucks; storage and wholesale) and downstream (refining into fuels or chemicals; marketing and distribution). Power plants using fossil or nuclear fuels. Geothermal energy for harnessing heat from the earth.
- Food and beverage production. From basic ingredients to elaborate desserts. From milk, to juices and other beverages. Cold chain to keep produce fresh, drinks and frozen foods at a set temperature. Desalination plants to transform seawater into drinking water for arid areas and various tropical islands.
- Pharmaceuticals and biotech production. Medicines and vaccines that treat illnesses and help restore bodies and minds to their top conditions.
- Semiconductor manufacturing: Microchips that go into all electronics, including smartphones, tablets, computers, television sets, telecom networks, …
- Pulp and paper production. Newsprint, glossy paper, cardboard boxes, books, writing paper, …
- Production of construction materials and plastics. From roofing materials, to glassmaking for windows, to copper wiring for transporting electricity, and various plastics throughout houses and office buildings.
How are pipe fittings measured ?
- Pipe fittings are measured by their diameter, wall thickness (known as “schedule”), and shape or configuration. (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.
What does “schedule” mean for pipe fittings ?
What is schedule 40, sch80 ?
- 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.
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 45 SR or 90 LR mean for pipe fittings ?
- 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.
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 ?
- Larger numbers have smoother curves.
- Centerline radius is calculated based on diameter and number that precedes it. For example, a 10″ 6D has a 60″ centerline radius.
- Smoother curves are often used for applications with higher pressure, abrasion or corrosion.
Who decides on standards and specifications for butt weld fittings ?
- Manufacturers of butt weld pipe fittings have to meet specifications and requirements of many organizations, to assure quality, compatibility and performance of their products.
- Key national and international standards organizations focus on materials and end-user industries, including American Society for Testing and Materials (ASTM), American Society of Mechanical Engineers (ASME), International Organization for Standardization (ISO), Norway’s NORSOK, …
- Some international organizations also focus on quality standards across all industries, such as International Organization for Standardization (ISO).
- Large industrial end-users also have their own programs to certify individual manufacturing plants as meeting their criteria to be listed on their Approved Manufacturers List (AML).
- All these certifications and approvals are valid for a specific period, and must be renewed regularly.
What is an MTR ?
- Material Test Reports (MTRs) are provided by manufacturers to certify physical properties and metal grade or alloy for each fitting, flange, pipe, or valve. This MTR is essential for demanding applications (pressure, temperature, corrosion, abrasion,…)
Why do manufacturers offer such a large variety of metals and materials ?
- Pipes and fittings are used in many applications and many industries that have widely different operating conditions.
- To reach best performance (resistance to various types of corrosive fluids, operating temperature, …) at acceptable costs, many metals have found unique niche applications in fittings.
Why choose a specific material, or grade, or schedule for a fitting ?
- Choice of material or grade or schedule is not made by distributors or by fitting manufacturers, but by engineers who design pipelines or systems based on performance requirements and acceptable costs.
- Engineers take into account key operating conditions and environment: pressure, temperature, abrasion, corrosion, vibrations, …
- Fitting materials also have to be chemically compatible with pipe materials to which they are connected to avoid inter-metal corrosion, and for weldability.
- Finally, cost of various materials varies greatly.
What does “high yield” (“HY”) mean for pipe fittings ?
- Yield strength refers to ability of materials to maintain a load or pressure without permanent deformation. (In this case, yield does not refer to manufacturing productivity of materials or equipment.)
- Fitting design is based on yield strength.
- Steel products do not all have similar potential. Yield strength can be changed by steel thickness, its chemical composition and heat treatments.
What is the difference between a manufacturer and a supplier of fittings ?
- Manufacturers own machines, presses and equipment to actually make fittings from pipe or plate.
- Suppliers are intermediaries between manufacturers and end-users: suppliers can be wholesalers, distributors, EPCs, …
- In some cases, end-users need to speak directly to manufacturers to get the fittings they need when they need them.
What is the difference between a destructive and a non-destructive test ?
- After a destructive test, fittings can no longer be used in the field, because they were bent, pulled or abused until breakage point. For this reason, destructive tests can only be performed on a small sample of fittings; otherwise, all fittings would be destroyed during tests.
- A non-destructive test measures performance for regular operating conditions, or by means that do not destroy the fitting.
What are most frequent destructive tests for fittings?
- Bending: fittings are bent until deformation appears on their side, face or root.
- Charpy impact: named after Georges Charpy who developed it, this test measures toughness of a fitting by determining the amount of energy absorbed during its fracture from impacts.
- Corrosion: fittings are exposed to corrosive fluids or materials until corrosion appears.
- Metallographic: this test studies physical structure and components of metal samples, typically by microscopy. Samples are taken from actual fittings.
- Tension: fittings are stretched until deformation appears; measures are taken for strength, yield, elongation.
What are most frequent non-destructive tests for fittings?
- Dye or liquid penetrant: low-cost test to detect surface hairline cracks or porosity in fittings, by applying a special liquid to its surface.
- Ferrite content: ferrite content in Duplex, Super Duplex and stainless steel has to be just right to achieve yield strength, fracture toughness and corrosion resistance. Ferrite content is measured in weld seams by magnetic induction.
- Hydrostatic: a fitting is filled with a liquid, often colored water, and pressure is applied; measurements are taken to see if there is pressure loss due to any defects.
- Magnetic particles: uses a magnetic field to detect surface or slightly subsurface discontinuity or weakness in a fitting.
- Macrography: makes photographs, sometimes in 3 dimensions, of items visible to naked eye.
- Micrography: uses microscopes to make photographs of metal and obtain information about its properties.
- Pneumatic pressure: a fitting is filled with pressurized air; measurements are taken to see if there is pressure loss due to any defects.
- Positive material identification: analysis of a metal alloy by identifying percentage for each of its elements. Uses specialty equipment, including X-ray fluorescence or optical emission spectrometry.
- Radiography: uses X-rays or gamma rays to detect any weakness in fittings.