Pipe (material)

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

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 is removed from the outside and inside surfaces and the weld zone is heat treated, so the seam is generally not 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.

Plastic pipe is generally extruded.

Materials

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 may be made from black or galvanized steel, copper, and ductile iron.

Plastic pipes are also widely used for their light weight, chemical resistance, and non-corrosive properties. Plastic pipe materials include PVC, polyethylene, and ABS.

Pipe may also be made from concrete or clay. These pipes are usually used for low pressure applications such as gravity flow or drainage.

Sizes

Many different standards exist for pipe sizes, and their prevalance varies depending on industry and geographical area. The pipe size designation generally includes two numbers; one that indicates the outside 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 in the US, and BS 1600 and BS 1387 in the United Kingdom.

In Europe, pressure piping uses the same pipe ID's and wall thicknesses as Nominal Pipe Size, but labels them with a metric Diametre 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 DIN 2448, 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 OD's than IPS.

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.

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.

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) Other pipe threads include Dryseal (NPTF), and British standard pipe thread (BSP).

Copper pipes are typically joined by soldering. Plastic pipes may be joined by solvent welding, heat fusion, or elastomeric sealing.

If frequent disconnection will be required, gasketed pipe flanges provid better reliability than threads. Some thin-walled pipes of ductile material, such as the smaller copper water pipes found in homes, may be joined with compression fittings

stainless steel 316L flange pipe

stainless steel 304L flange pipe