Manufacturing of Line Pipe
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 It is available in the following specifications: ASTM A-120 (withdrawn 1988).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.
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.
5. 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 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 WELD PIPE
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 nugget.br/
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 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.
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 nugget.br/
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 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, 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.
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.
Ref: http://midstate-steel.com/how-pipe-is-manufactured.html
This post is based on SDGE 41-06.1 and TWI:
Fracture Toughness Tests
For pipe purchased to order, drop weight tear (DWT) tests shall be made on sizes 20” diameter and larger, regardless of grade. Two specimens from one length of pipe from each heat shall be tested, in addition to the sampling frequency established in Table 18 of API 5L. The specimens shall be tested in accordance with API RP 5L3 and meet the requirements of API 5L 9.9 and Annex G8 with the following exception: 100% of heats shall exhibit a fracture appearance shear area of 80% or more. The average shear fracture area shall be 85% as per API 5L G.3.18. The maximum DWT sample temperature at the time of testing shall be +32ºF unless specified by the Company.
Charpy impact tests shall be made on pipe 6" diameter and larger. The tests shall meet the requirements of API 5L 9.8, 10 and Annex G. Full size transverse Charpy tests shall be performed where possible. If the pipe wall thickness does not permit machining of full size specimens or if impact toughness of full size samples exceeds the capacity of the Charpy test machine, then sub-size samples as per API 5L Table 22 may be substituted with proportional adjustments in the required energy.
The minimum average Charpy absorbed energy requirement for each set of three samples shall be calculated using the greater of 20 ft-lbs or the value calculated using the following equation:
Cv = 0.0117 (0.8Sy)2 (Rt)0.333(Pc)
Where
Cv = Charpy energy (ft-lbs)
Sy = specified minimum yield strength (ksi)
R = pipe outside radius (inches)
t = nominal pipe thickness (inches)
PC = 1 for full size, 0.67 for 2/3 size, 0.50 for 1/2 size and 0.33 for 1/3 size
The lowest measured absorbed energy for any single sample shall be at least 75% of the required minimum average absorbed energy.
When drop weight tear (DWT) tests are not performed the shear appearance of the Charpy test samples shall be measured. The requirements of API 5L 9.8 shall apply, except that each heat shall show an average shear area of at least 80%. When shear area measurements are required the test temperature shall be no higher than the temperature shown in Table 4. When Charpy shear measurements are not required the test temperature shall be +32°F unless otherwise specified.
Charpy Testing
Charpy impact testing involves striking a standard notched specimen with a controlled weight pendulum swung from a set height. The standard Charpy-V notch specimen is 55mm long, 10mm square and has a 2mm deep notch with a tip radius of 0.25mm machined on one face. The specimen is supported at its two ends on an anvil and struck on the opposite face to the notch by the pendulum. The amount of energy absorbed in fracturing the test-piece is measured and this gives an indication of the notch toughness of the test material. The pendulum swings through during the test, the height of the swing being a measure of the amount of energy absorbed in fracturing the specimen. Conventionally, three specimens are tested at any one temperature and the results averaged.
Charpy tests show whether a metal can be classified as being either brittle or ductile. This is particularly useful for ferritic steels that show a ductile to brittle transition with decreasing temperature. A brittle metal will absorb a small amount of energy when impact tested, a tough ductile metal absorbs a large amount of energy. The appearance of a fracture surface also gives information about the type of fracture that has occurred; a brittle fracture is bright and crystalline, a ductile fracture is dull and fibrous. The percentage crystallinity is determined by making a judgement of the amount of crystalline or brittle fracture on the surface of the broken specimen, and is a measure of the amount of brittle fracture.
Lateral expansion is a measure of the ductility of the specimen. When a ductile metal is broken, the test-piece deforms before breaking, and material is squeezed out on the sides of the compression face. The amount by which the specimen deforms in this way is measured and expressed as millimetres of lateral expansion.
When reporting the results of a Charpy test, the absorbed energy (in J) is always reported, while the percentage crystallinity and lateral expansion are optional on the test report. It should be emphasised that Charpy tests arequalitative, the results can only be compared with each other or with a requirement in a specification - they cannotbe used to calculate the fracture toughness of a weld or parent metal.
Fig.1. Charpy testing machine and specimen arrangement
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