Pipe (material)
From Wikipedia, the free encyclopedia
- For structural pipe, see hollow structural section.
Pipe is a tube or hollow cylinder for the conveyance of fluid, gas and sometimes other materials. The terms 'pipe' and 'tubing' are almost interchangeable. 'Pipe' is generally specified by the internal diameter (ID) whereas 'tube' is usually defined by the outside diameter (OD) but may be specified by any combination of dimensions (OD, ID, wall thickness), depending upon which are considered the most important to the designer. 'Tube' is often made to custom sizes and may often have more specific sizes and tolerances than pipe. Also the term "tubing" can be applied to tubes of a non-cylindrical nature (i.e. square tubing). The term 'tubing' is more widely used in the USA and 'pipe' elsewhere in the world.
Both "pipe" and "tube" imply a level of rigidity and permanence, whereas a 'hose' is usually portable and flexible. Pipe may be specified by standard pipe size designations, such as Nominal Pipe Size (in the US), or by nominal, outside, or inside diameter and wall thickness. Many industrial and government standards exist for the production of pipe and tubing.
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[edit] Uses
- Domestic water systems
- Pipelines containing high pressure gas or fluid
- Scaffolding
- Structural steel
- As components in mechanical systems such as:
- Rollers in conveyor belts
- Compactors (Eg: steam rollers)
- Bearing casing
- Casing for concrete pilings used in construction projects
- High temperature or pressure manufacturing processes
- The petroleum industry:
- Oil well casing
- Oil refinery equipment
- The construction of high pressure storage vessels
[edit] Manufacture
There are three processes for metallic pipe manufacture. Seamless pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell. Seamless pipe provides the most reliable pressure retaining characteristics, and is often more easily available than welded pipe. Welded pipe is formed by rolling plate and welding the seam. The weld flash can be removed from the outside or inside surfaces using a scarfing blade. The weld zone can also be heat treated, so the seam is less visible. Welded pipe often has tighter dimensional tolerances than seamless, and can be cheaper if manufactured in the same quantities. Cast pipe is no longer very common, but still exists. Pipe is sometimes cast in a centrifuge.
Tubing, either metal or plastic, is generally extruded.
[edit] Materials
The manufacturing of pipe uses many materials including ceramic, metal, concrete, and plastic.
Pipe may be made from a variety of materials. In the past, materials have included wood and lead (Latin plumbum, from which we get the word plumbing).
Metal pipes are commonly made from unfinished, black (lacquer), or galvanized steel, brass, and ductile iron. Copper tubing is popular for plumbing systems.
Plastic tubing is widely used for its light weight, chemical resistance, non-corrosive properties, and ease of making connections. Plastic materials include polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyethylene (PE), cross-linked high-density polyethylene (PEX), polybutylene (PB), and acrylonitrile butadiene styrene (ABS), for example.
Pipe may also be made from concrete or ceramic. These pipes are usually used for low pressure applications such as gravity flow or drainage.
Concrete pressure pipe for water lines can be made in accordance with American Water Works Association ([1]) standards of C-303 or L-301. C-303 pipe has a round bar helically wound around the steel cylinder and all surfaces are then coated with cement mortar. C-301 is a prestressed pipe and is made using two different techniques. The first method has a steel cylinder which has been lined with concrete and after the concrete cures the prestressing wire is wound directly on the steel cylinder and the exterior is then coated with cement mortar. The second method encases the steel cylinder in concrete which is then prestessed after the concrete cures and the exterior is then coated with cement mortar. C-303 pipe can be manufactured in from 10" through 72" and C-301 goes from 36" through 144". Working pressure is generally less than 300 psi.
Reinforced concrete can be used for large diameter concrete pipes. This pipe material can be used in many types of construction and is often used in the transport of storm water. Usually such pipe will have a receiving bell or a stepped fitting, with various sealing methods applied at installation.
[edit] Sizes
Many different standards exist for pipe sizes, and their prevalence varies depending on industry and geographical area. The pipe size designation generally includes two numbers; one that indicates the outside (OD) or nominal diameter, and the other that indicates the wall thickness. In the early twentieth century, American pipe was sized by inside diameter. This practice was abandoned to improve compatibility with pipe fittings that must usually fit the OD of the pipe, but it has had a lasting impact on modern standards around the world.
In North America and the UK, pressure piping is usually specified by Nominal Pipe Size (NPS) and schedule (SCH). Pipe sizes are documented by a number of standards, including API 5L, ANSI/ASME B36.10M (Table 1) in the US, and BS 1600 and BS 1387 in the United Kingdom. Typically the pipe wall thickness is the controlled variable, and the Inside Diameter (I.D.) is allowed to vary. The pipe wall thickness has a variance of approximately 12.5 percent.
In Europe, pressure piping uses the same pipe IDs and wall thicknesses as Nominal Pipe Size, but labels them with a metric Diameter Nominal (DN) instead of the imperial NPS. For NPS larger than 14, the DN is equal to the NPS multiplied by 25. (Not 25.4) This is documented by EN 10255 (formerly DIN 2448 and BS 1387) and ISO 65, and it is often called DIN or ISO pipe.
Japan has its own set of standard pipe sizes, often called JIS pipe.
The Iron pipe size (IPS) is an older system still used by some manufacturers and legacy drawings and equipment. The IPS number is the same as the NPS number, but the schedules were limited to Standard Wall (STD), Extra Strong (XS), and Double Extra Strong (XXS). STD is identical to SCH 40 for NPS 1/8 to NPS 10, inclusive, and indicates .375" wall thickness for NPS 12 and larger. XS is identical to SCH 80 for NPS 1/8 to NPS 8, inclusive, and indicates .500" wall thickness for NPS 8 and larger. Different definitions exist for XXS, but it is generally thicker than schedule 160.
Another old system is the Ductile Iron Pipe Size (DIPS), which generally has larger ODs than IPS.
Copper plumbing tube for residential plumbing follows an entirely different size system, often called Copper Tube Size (CTS); see domestic water system. Its nominal size is neither the inside nor outside diameter. Plastic tubing, such as PVC and CPVC, for plumbing applications also has different sizing standards.
Agricultural applications use PIP sizes, which stands for Plastic Irrigation Pipe. PIP comes in pressure ratings of 22 psi, 50 psi, 80 psi, 100 psi, and 125 psi and is generally available in diameters of 6", 8", 10", 12", 15", 18", 21", and 24".
[edit] Standards
The manufacture and installation of pressure piping is tightly regulated by the ASME Boiler and Pressure Vessel Code. This code has the force of law in Canada and the USA. Europe has an equivalent system of codes. Pressure piping is generally pipe that must carry pressures greater than 10 to 25 atmospheres, although definitions vary. To ensure safe operation of the system, the manufacture, storage, welding, testing, etc. of pressure piping must meet stringent quality standards.
Manufacturing standards for pipes commonly require a test of chemical composition and a series of mechanical strength tests for each heat of pipe. A heat of pipe is all forged from the same cast ingot, and therefore had the same chemical composition. Mechanical tests may be associated to a lot of pipe, which would be all from the same heat and have been through the same heat treatment processes. The manufacturer performs these tests and reports the composition in a mill traceability report and the mechanical tests in a material test report, both of which are referred to by the acronym MTR. Material with these associated test reports is called traceable. For critical applications, third party verification of these tests may be required; in this case an independent lab will produce a certified material test report, and the material will be called certified.
Maintaining the traceability between the material and this paperwork is an important quality assurance issue. QA often requires the heat number to be written on the pipe. Precautions must also be taken to prevent the introduction of counterfeit materials.
Some widely used pipe standards are:
- The API range. Eg: API 5L Grade B
- ASME SA106 Grade B (Seamless carbon steel pipe for high temperature service)
- ASTM A312 (Seamless and welded austenitic stainless steel pipe)
See this site for more specification summaries.
[edit] Installation
Pipe installation is often more expensive than the material and a variety of specialized tools, techniques, and parts have been developed to assist this. An example tool is the pipe wrench.
[edit] Joining
Pipes are commonly joined by welding or by using pipe threads. The most common pipe thread in North America is the National Pipe Thread (NPT) or the Dryseal (NPTF) version. Other pipe threads include the British standard pipe thread (BSPT), the garden hose thread (GHT), and the fire hose coupling (NST).
Copper pipes are typically joined by soldering, brazing, compression, flaring, or crimping. Plastic pipes may be joined by solvent welding, heat fusion, or elastomeric sealing.
If frequent disconnection will be required, gasketed pipe flanges or union fittings provide better reliability than threads. Some thin-walled pipes of ductile material, such as the smaller copper or flexible plastic water pipes found in homes for ice makers and humidifiers, for example, may be joined with compression fittings.
Mechanical grooved couplings or Victaulic joints are also frequently used for frequent disassembly & assembly. Developed in the 1920s, these mechanical grooved couplings can operate up to 1,200psi working pressures and available in materials to match the pipe grade.
[edit] Fittings and valves
Fittings are also used to split or join a number of pipes together, and for other purposes. A broad variety of standardized pipe fittings are available. Valves control fluid flow. The piping and plumbing fittings and valves articles discuss them further.
[edit] Hangers
Pipes are hung from devices called pipe hangers, which may incorporate springs and/or dampers to compensate for thermal expansion or to provide vibration isolation
[edit] Cleaning
The inside of pipes can be cleaned with the tube cleaning process, if they are contaminated with debris or fouling.
[edit] See also
- Piping
- National pipe thread
- Nominal Pipe Size
- British standard pipe thread
- Hollow structural section
- Plumbing
- Pipeline transport
- Pipe (disambiguation page)
- Trap (plumbing)
- Water pipe
- Hydraulic pipes
- Reinforced Thermoplastic Pipes
- Plastic Pressure Pipe Systems
[edit] External links
Critical Fluid Handling with Tubes
[edit] References
- Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). in ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain: Machinery's Handbook, 26th edition, New York: Industrial Press Inc.. ISBN 0-8311-2635-3.
- Nayyar, P.E., Mohinder L. (2000). "A1", in Mohinder L. Nayyar, P.E.: Piping Handbook, 7th, New York: McGraw-Hill. ISBN 0-07-047106-1.
