Linepipe Manufacture

Line pipe is a type of pipe that is manufactured from high strength carbon steel. It is typically made according to metallurgical specifications that were developed by the American Petroleum Institute (API). Line pipe can be used to build pipelines that transport a variety of resources including natural gas, oil, petroleum, and water. This pipe is available in a variety of diameters ranging from 2 inches to 48 inches. Line pipe can include either seamless or welded carbon steel or stainless steel piping. Because line pipe needs to withstand high pressures, there are important tests done on line pipe to ensure it meets all of the requirements of steel chemistry, strength, toughness, and dimensional characteristics. Using line pipe that meets the set criteria will ensure safe and reliable pipeline service.

Line pipe
The size and diameter of line pipe that is required for a pipeline can vary based on the amount of gas or liquid that a pipe is intended to carry as well as the pressures that a line pipe must withstand. For example, in most cases a mainline, the principal pipeline that delivers natural gas, will require line pipe that is around 16 to 48 inches in diameter. Smaller pipelines that deliver gas to the mainline or take gas from a mainline can be constructed of 6 to 16 inch diameter line pipe. One can determine the necessary diameter required for a pipeline by considering the volume of gas or liquid that the line pipe will be carrying as well as the pressure at which this will be transported.

The thickness requirements for line pipe are determined by the maximum operating pressure required for a pipeline. This is based on published standards and federal regulations. Following proper safety regulations when selecting and installing line pipe, will ensure proper pipeline operation and prevent dangerous or hazardous situations.

Production of steel pipe is grouped into two general categories: welded and seamless.  There are many methods of producing steel pipe in current use. However, most of the pipe produced in the United States is made by either the Continuous Weld, the Electric Resistance Weld, the Double Submerged Arc Weld or the Seamless method.

Continuous weld pipe

Continuous weld pipe is produced in sizes from NPS Va to NPS 4. Production begins with coiled skelp of the required width and thickness for the size and weight of pipe to be made. Successive coils of steel are welded end to end to form an endless ribbon of steel. The coiled steel is fed into a roll leveler and then into agas fired furnace where it is heated to the required temperature for forming and welding. The forming rolls at the exit end of the furnace shape the heated skelp into an oval. The edges of the skelp are then firmly pressed together by welding rolls to obtain a forged weld. The heat of the skelp, combined with the pressure exerted by the rolls form the weld. No metal is added in the operation. The final rolls on the mill reduces the diameter and wall thickness to bring the pipe to its finished dimensions.

Synchronized with the speed of the pipe as it emerges from the final rolls is a rotary saw which cuts the pipe to its desired length. The pipe is then cooled, descaled, straightened, inspected. tested hydrostatically, coated as required and end finished. Continuous weld pipe is commonly used for the conveyance of water. air. gas, steam; for sprinkling systems, water wells. fencing. and a multitude of structural applications. C.W. pipe is generally the lowest cost steel piping material available. It is available in the following specifications: ASTM A-120 (withdrawn 1988). A-53. A-501. A-589, A-618. and API5L.

Continuous weld pipe is normally produced in three weights:
Standard. Extra Heavy, and Double Extra Heavy NPS Va to NPS 4 Lighter weights than standard are available in certain sizes. Continuous weld pipe is available with square ends. beveled 30° for welding, threaded both ends, threaded and coupled and victaulic grooved for use with victaulic couplings. Surface finishes are available in Black (oiled). Galvanized. and Bare. CW. Pipe is also supplied with Inorganic coatings (adodic chromate, oxide and vitress enamels); Organic coatings (paints. varnishes. lacquers. rubber, and plastics such as x-tru coat and Scotchkote); Bituminous coatings (asphalt and coal tar).

Continuous Weld pipe is available in 21 foot uniform lengths. single random lengths from 16 foot to 22 foot and double random lengths from 38 foot to 42 foot. Continuous Weld pipe in sizes NPS 1V2 and smaller are normally put in standard bundles as indicated in the following chart.

Continuous weld steps of manufacture

  1. Coiled strip is loaded onto feed table.
  2. Strip is fed into roller leveler. 
  3. Ends of strip are sheared.
  4. Leading end of coil is flash welded to trailing end of previous coil.
  5. Strip is formed into loop.
  6. Coil is delivered into furnace.
  7. Strip is heated in furnace to approximately 2450°F, strip edge is heated to 2600°F.
  8. Forming rolls bend strip into an oval. At the welding stand the heat in the skelp and the pressure of the rollsforms the weld.
  9. Pipe is stretch reduced where the desired 00 and wall thickness are obtained.
  10. Flying cutoff saw cuts pipe into double lengths.
  11. Final 00 sizing on sizing mill.
  12. Pipe is cut to finished length, straightened and inspected.
  13. Pipe is hydrostatically tested, end finished, stenciled, and coated as required.

Electric Resistance Weld pipe

Electric Resistance Weld pipe is normally produced in sizes from 2% inch 00 NPS 2 thru 24 inch 00. (NPS 24) ERW is produced from individual sheets or continuously from rolls of skelp. There are two important differences. In the production of ERW pipe as versus CW pipe. ERW pipe is cold formed into a cylindrical shape rather than hot formed. An electric current rather than a flame is used to heat the edges of the strip for the fusion weld. Revolving copper discs serve as electrodes and raise the temperature to about 2600°F for effective welding. As in CW pipe, no extraneous metal is added; in fact, due to the extreme pressure of the rolls, steel is extruded on both the inside and outside of the pipe at the point of the weld. This is called flash and is removed by stationary cutters while still white hot.

ERW Steel pipe process

As in CW production. ERW pipe is subject to numerous finishing operations. ERW pipe is primarily used as API Line pipe for the transmission of gas and oil. It is also used for the transmission of water. Under AWWA specifications. as piling and slurry pipe and in mechanical applications.
ERW pipe is available in the following most common specifications: ASTM A-53 Grade;A & B;A-135
A-252 Grade 1. 2, 3;API5L Grade A & B; and API5LX42 thru X-55.

ERW pipe is available in lengths from single random to 80 feet. ERW pipe is available with square ends or beveled for welding, threaded and coupled and victaulic grooved. Surface finish are available in black or bare, or with protective coatings, as described in C.W. section.

Major purchasers of ERW pipe are:

Utility Companies,Oil Companies,Steel Fabricators, Piling Contractors,Dredging Contractors,Water Well Contractors,Pipe Distributors, Pipe Line Companies, and Federal, State. and Local Governmental Agencies.

Electric resistance weld steps of manufacture
  1. Coils of strip steel or skelp on feed ramp. From this position it is uncoiled, flattened, and the leading edge of the coil is sheared.
  2. First forming section transforms strip into a round pipe section.
  3. Fin pass section finishes rounding process and prepares edges of strip for welding .
  4. The edges of the strip are heated to 2500°F by high frequency welder. The edges are squeezed together by pressure.
  5. Weld is inspected electronically for some specifications.
  6. Seam is normalized.
  7. Weld is cooled by air and water.
  8. Pipe is sized and straightened.
  9. Pipe is cut to required length by flying cut-off saw.
  10. Pipe is visually inspected.
  11. Pipe is hydro-statically tested.
Final finishing includes inspection, end finishing, coated as required, and stenciled.

Seamless pipe

Seamless pipe is produced domestically in sizes NPS 'Ie through NPS 26 00. Seamless pipe is produced without a seam or weld in the circumference. Seamless pipe is produced by a variety of methods. To put it in its most simple terms, seamless pipe is produced by piercing a solid billet of deoxidized and conditioned steel, which has been properly prepared and heated to the proper temperature. It is then processed through a series of mills where the pipe is finished to its prescribed dimensions. Seamless sizes over 14 inch 00 are usually rotary rolled from 14 inch seamless shells which expand the diameter and reduce the wall thickness to the approximate dimensions required. Small sizes of seamless pipe are generally obtained through the use of a stretch reduced mill. In this process the outside diameter and the wall thickness of the pipe is reduced through a series of rolls. Seamless pipe goes through various finishing operations including straightening, inspection, testing, and end finishing. Seamless pipe is widely used in construction, oil refining, chemical and petro-chemical industries.

Seamless pipe process

Seamless pipe is available In the following specifications: ASTM A-53 Grades A & B; A-106 Grades A.B, and C; A-252 Grades 1,2,and 3; A-333 Grades 1 through 9; A-335 Grades P-1 through P-22; A-501, A-523, A-589, API5L Grades A & B, and API5L X-42 through X-65.

It is common practice to dual stencil seamless pipe with API5L and ASTM A-53 monograms. Seamless pipe is available in single random and double random lengths. It is not normally supplied in uniform lengths. End finishes for A-53 include plain ends, either beveled or square cut, grooved for victaulic couplings and threaded and coupled. Grades other than A-53 are normally supplied in plain end only, either square cut or beveled. In sizes 6% and over, in thicknesses 3/4 inch and over, a "two-step" bevel is available.

Seamless pipe is available in black, bare, galvanized, or with protective coatings as described in C.W. section. The following are major purchasers of seamless pipe: Pipe Distributors, Plumbing & Heating Supply Houses, Mechanical Contractors, Oil and Gas Companies, Chemical Companies, Power Generation Equipment Manufacturers, Railroads, Shipbuilders, Utility Companies, Governmental Agencies, Pipe Fabricators and Water Well Contractors.

Double submerged arc welded pipe (DSAW)

Double submerged arc welded pipe (DSAW) derives its name from the welding process wherein the welding arc is submerged in flux while the welding takes place. Both inside and outside welds are required and are usually accomplished in separate processes, hence the word "double." These separate welds consume a portion of the other resulting in a single high quality weld
DSAW pipe is produced in sizes from 18" through 72" 00 and wall thicknesses from .250" through 1.5".

Two different processes are used to manufacture DSAW pipe; the pyramid rolls method, and the U-O-E method. The difference in the processes is found only in the method of forming the cylinder. In the pyramid rolls process the cylinder is formed between 3 rolls arranged in a pyramidal fashion. As the name implies; the U-O-E method uses a "U" press, and "0" press for forming. Other parts of the process such as finishing and inspection are similar. Both processes use flat steel plate as the raw material.

DSAW steel pipe

DSAW pipe mayor may not be cold expanded. Cold expansion is a process where the pipe is expanded (up to 1_5%) to obtain its final 00 dimension. In the process, a gain of yield strength results. Expansion is most often utilized in a U-O-E mill due to the need to recover the yield strength lost during forming in the "0 press, DSAW pipe is available in the following grades:
ASTM A134, A139, A252, A671, A672, A690, A691, CSA (Canadian) - Z245.1 and custom specifications. API 2B, 5LB, 5LX-42 thru 5LX-80

DSAW pipe is normally produced in double random lengths with square ends or beveled for welding. It is usually furnished bare but varnish is also offered. A wide range of external coatings and internal linings are available with DSAW pipe. These include fushion bond epoxy (FBE) coatings and thin film epoxy linings. DSAW pipe is used in high pressure gas and oil transmission lines (both onshore and offshore), structural members and pipe piles. Major purchasers include liquid and gas transmission companies, hammer companies, construction contractors, platform fabricators, government agencies and pipe distributors.

Spiral Weld Pipe

Spiral Weld Pipe, as the name implies, is a steel pipe which has a seam running its entire length in a spiral form. In the past, due to the method of manufacture, Spiral Welded pipe was relegated to low pressure and structural applications. With the development of the Submerged Arc Welding process, the production of large hot rolled coils of sufficient width and the development of dependable non-destructive testing methods, it is now possible to produce Spiral Weld pipe for high pressure service. 
Spiral weld pipe process
Present Spiral Weld mills consist of a de-coiling device (in the case of strip base material) or a plate preparation table (where the base material is in plate form) a strip connecting welder, straightening rollers, edge preparation tools (shearing and trimming), prebending devices, a three roller bending and cage forming system, an internal welder, an external welder (both Submerged Arc), ultrasonic testing apparatus and cutting devices. The material passes through all these production stages continuously. The angle between the flat strip being I fed into the machine and the finished pipe leaving the machine controls the pipe diameter in ratio to strip width and the angle of the weld in the pipe. 

Because of the method of manufacture, a wide variety of diameters can be produced. The diameter tolerance is small, particularly with regard to ovality; and the pipe, due to its axial symmetry, has an inherent straightness. The length range is infinite and is controlled only by the economics of transportation. Spiral Weld Pipe is used for dredging, slurry, water and other pipelines, as well as piling and structural applications. Spiral Weld Pipe is produced in accordance with the dimensional and tolerance requirements of various ASTM, AWWA, and API Specifications.



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