Pipes & Tubes

Pipes

Steel Pipe (Metal Pipe) is the most common material for pipe. A pipe is a hollow tube with round cross section for the conveyance of products. The products include fluids, gas, pellets, powders and more. The word pipe is used as distinguished from tube to apply to tubular products of dimensions commonly used for pipeline and piping systems. On this website, metal pipe conforming to the dimensional requirements of: ASME B36.10 Welded and Seamless Wrought Steel Pipe and ASME B36.19 Stainless Steel Pipe will be discussed.

Trupply sells only metal pipes as seamless pipe, welded (ERW Pipe) & galvanized pipe. Both Seamless pipe and ERW Pipes are available in broad schedule ranges, though Schedule 40 Steel Pipe is the most common pipe wall thickness. Make sure you differentiate between true schedule 40 steel pipe and standard pipe as they differ in wall thicknesses for 12" and bigger pipe sizes.

Pipe or Tube?

In the world of piping, the terms pipe and tube will be used. Pipe is customarily identified by "Nominal Pipe Size" (NPS), with wall thickness defined by "Schedule number" (SCH). Tube is customarily specified by its outside diameter (O.D.) and wall thickness (WT), expressed either in Birmingham wire gage (BWG) or in thousandths of an inch.

Pipe:  NPS 1/2-SCH 40 is even to outside diameter 21.3 mm (27/32 inch) with a wall thickness of 2.77 mm (7/64 inches).
Tube:  1/2" x 1,5 is even to outside diameter 12.7 mm (1/2 inch) with a wall thickness of 1.5 mm (1/16 inches).

The principal uses for tube are in Heat Exchangers, instrument lines and small interconnections on equipment such as compressors, boilers etc..

Materials for Pipe

Engineering companies have materials engineers to determine materials to be used in piping systems. Most pipe is of carbon steel (depending on service) is manufactured to different ASTM standards.

Carbon-steel pipe is strong, ductile, weldable, machinable, reasonably durable and is nearly always cheaper than pipe made from other materials. If carbon-steel pipe can meet the requirements of pressure, temperature, corrosion, resistance and hygiene, it is the natural choice.

Iron pipe is made from cast-iron and ductile-iron. The principal uses are for water, gas and sewage lines.

Plastic pipe may be used to convey actively corrosive fluids, and is especially useful for handling corrosive or hazardous gases and dilute mineral acids.

Other Metals and Alloys pipe made from copper, lead, nickel, brass, aluminum and various stainless steels can be readily obtained. These materials are relatively expensive and are selected usually either because of their particular corrosion resistance to the process chemical, their good Heat Transfer, or for their tensile strength at high temperatures. Copper and copper alloys are traditional for instrument lines, food processing and Heat Transfer equipment. Stainless steels are increasingly being used for these.

ASTM Materials

  • A106 = This specification covers carbon steel pipe for high-temperature service. A106 Grade B is the most commonly used seamless pipe.

  • A335 = This specification covers seamless ferritic alloy-steel pipe for high-temperature service.

  • A333 = This specification covers wall seamless and welded carbon and alloy steel pipe intended for use at low temperatures.

  • A312 = Standard specification for seamless pipe, straight-seam welded pipe (ERW Pipe or DSAW Pipe), and cold worked welded austenitic stainless steel pipe intended for high-temperature and general corrosive service.

Lined Pipe

Some materials described above, have been combined to form lined pipe systems.
For example, a carbon steel pipe can be internally lined with material able to withstand chemical attack permits its use to carry corrosive fluids. Linings (Teflon®, for example) can be applied after fabricating the piping, so it is possible to fabricate whole pipe spools before lining.

Other internal layers can be: glass, various plastics, concrete etc., also coatings, like Epoxy, Bituminous Asphalt, Zink etc. can help to protect the inner pipe.

Many things are important in determining the right material. The most important of these are pressure, temperature, product type, dimensions, costs etc..

Nominal Pipe Size

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. The name NPS is based on the earlier "Iron Pipe Size" (IPS) system.

That IPS system was established to designate the pipe size. The size represented the approximate inside diameter of the pipe in inches. An IPS 6" pipe is one whose inside diameter is approximately 6 inches. Users started to call the pipe as 2inch, 4inch, 6inch pipe and so on. To begin, each pipe size was produced to have one thickness, which later was termed as standard (STD) or standard weight (STD.WT.). The outside diameter of the pipe was standardized. For example a 6" schedule 40 steel pipe has an OD of 6.625 inch and an ID of 6.065.

As the industrial requirements handling higher pressure fluids, pipes were manufactured with thicker walls, which has become known as an extra strong (XS) or extra heavy (XH). The higher pressure requirements increased further, with thicker wall pipes. Accordingly, pipes were made with double extra strong (XXS) or double extra heavy (XXH) walls, while the standardized outside diameters are unchanged. Note that on this website only terms XS and XXS are used.

Pipe Schedule

So, at the IPS time only three wall thicknesses were in use. In March 1927, the American Standards Association surveyed industry and created a system that designated wall thicknesses based on smaller steps between sizes. The designation known as nominal pipe size replaced iron pipe size, and the term schedule (SCH) was invented to specify the nominal wall thickness of pipe. By adding schedule numbers to the IPS standards, today we know a range of wall thicknesses, namely:

SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS and XXS.

Nominal pipe size (NPS) is a dimensionless designator of pipe size. It indicates standard pipe size when followed by the specific size designation number without an inch symbol. For example, NPS 6 indicates a pipe whose outside diameter is 168.3 mm (6-7/16 inches).

The NPS is very loosely related to the inside diameter in inches, and NPS 12 and smaller pipe has outside diameter greater than the size designator. For NPS 14 and larger, the NPS is equal to 14inch.

For a given NPS, the outside diameter stays constant and the wall thickness increases with larger schedule number. The inside diameter will depend upon the pipe wall thickness specified by the schedule number.

Summary:
Pipe size is specified with two non-dimensional numbers,

nominal pipe size (NPS)

schedule number (SCH)

and the relationship between these numbers determine the inside diameter of a pipe.

Stainless Steel Pipe dimensions determined by ASME B36.19 covering the outside diameter and the Schedule wall thickness. Note that stainless wall thicknesses to ASME B36.19 all have an "S" suffix. Sizes without an "S" suffix are to ASME B36.10 which is intended for carbon steel pipes.

Types, Lengths and Ends of Pipes

Pipe manufacturing refers to how the individual pieces of pipe are made in a pipe mill; it does not refer to how the pieces are connected in the field to form a continuous pipeline. Each piece of pipe produced by a pipe mill is called a joint or a length (regardless of its measured length). In some cases, pipe is shipped to the pipeline construction site as "double joints", where two pieces of pipe are pre-welded together to save time. Most of the pipe used for oil and gas pipelines is seamless or longitudinally welded, although spirally welded pipe is common for larger diameters.

Steel Pipes are manufactured in 4 versions:

1. Longitudinally Welded SAW   2. Spiral Welded
3. Electric Resistance Welded (ERW Pipe)   4. Seamless Pipe

 

Welded Pipe

Welded pipe (pipe manufactured with a weld) is a tubular product made out of flat plates, known as skelp that are formed, bent and prepared for welding. The most popular process for large diameter pipe uses a longitudinal seam weld.

Spiral welded pipe is an alternative process, spiral weld construction allows large diameter pipe to be produced from narrower plates or skelp. The defects that occur in spiral welded pipe are mainly those associated with the SAW weld, and are similar in nature to those for longitudinally welded SAW pipe.

Electric Resistance Welded (ERW Pipe) and High Frequency Induction (HFI) Welded Pipe

Originally this type of pipe, which contains a solid phase butt weld, was produced using resistance heating to make the longitudinal weld (ERW), but most pipe mills now use high frequency induction heating (HFI) for better control and consistency. However, the product is still often referred to as ERW pipe, even though the weld may have been produced by the HFI process.

The defects that can occur in ERW/HFI pipe are those associated with strip production, such as laminations and defects at the narrow weld line. Lack of fusion due to insufficient heat and pressure is the principal defect, although hook cracks can also form due to realignment of nonmetallic inclusions at the weld interface. Because the weld line is not visible after trimming, and the nature of the solid phase welding process, considerable lengths of weld with poor fusion can be produced if the welding parameters fall outside the set limits. In addition, early ERW pipe was subject to pressure reversals, a problem that results in failure in service at a lower stress than that seen in the pre-service pressure test. This problem is caused by crack growth during the pressure test hold period, which in the case of early ERW pipe was due to a combination of low weld line toughness and lack of fusion defects.

Seamless Pipe - Plug Mill Process

This process is used to make larger sizes of seamless pipe, typically 6 to 16 inches (150 to 400 mm) diameter. An ingot of steel weighing up to two tons is heated to 2,370°F (1,300°C) and pierced. The hole in the hollow shell is enlarged on a rotary elongator, resulting in a short thick-walled tube known as a bloom.

An internal plug approximately the same diameter as the finished diameter of the pipe is then forced through the bloom. The bloom containing the plug is then passed between the rolls of the plug mill. Rotation of the rolls reduces the wall thickness. The tube is rotated through 90° for each pass through the plug mill to ensure roundness. The tube is then passed through a reeling mill and reducing mill to even out the wall thickness and produce the finished dimensions. The tube is then cut to length before heat treatment, final straightening, inspection, and hydrostatic testing.

Seamless Pipe - Mandrell Mill Process

This process is used to make smaller sizes of seamless pipe, typically 1 to 6 inches (25 to 150 mm) diameter. The ingot of steel is heated to 2,370°F (1,300°C) and pierced. A mandrel is inserted into the tube and the assembly is passed through a rolling (mandrel) mill. Unlike the plug mill, the mandrel mill reduces wall thickness continuously with a series of pairs of curved rollers set at 90° angles to each other. After reheating, the pipe is passed through a multi-stand stretch-reducing mill to reduce the diameter to the finished diameter. The pipe is then cut to length before heat treatment, final straightening, inspection, and hydrostatic testing.

Seamless Pipe - Extrusion Process

This process is used for small diameter tubes only. The bar stock is cut to length and heated to 2,280°F (1,250°C) before being sized and descaled. The billet is then extruded through a steel die. After extrusion, the final tube dimensions and surface quality are obtained with a multi-stand reducing mill.

Length of Pipes

Piping lengths from the factory not exactly cut to length but are normally delivered as:

Single random length has a length of around 5-7 meter (16.4 – 22.9 feet)

Double random length has a length of around 11-13 meter (36 – 42.6 feet)

Shorter and longer lengths are available, but for a calculation, it is wise, to use this standard lengths; other sizes are probably more expensive.

Ends of pipes

For the ends of pipes are 3 standard versions available.

•Plain Ends (PE)

•Threaded Ends (TE)

•Beveled Ends (BE)

The PE pipes will generally be used for the smaller diameters pipe systems and in combination with Slip On flanges and Socket Weld fittings and flanges.

The TE implementation speaks for itself, this performance will generally used for small diameters pipe systems, and the connections will be made with threaded flanges and threaded fittings.

Beveled ends and Root face

The BE implementation is applied to all diameters of buttweld flanges or buttweld fittings, and will be directly welded (with a small gap 3-4 mm) to each other or to the pipe. Ends are mostly be beveled to angle 30° (+ 5° / -0°) with a root face of 1.6 mm (± 0.8 mm).

Pipe Dimensions & Weights