ERW (Electric Resistance Welded)
Electric Resistance Weld pipe is normally produced in sizes from 2.375” OD through 24” OD. ERW is produced from individual sheets or continuously from rolls of skelp. There are two important differences in the production of ERW pipe versus Continuous Weld pipe. ERW pipe is cold formed into a cylindrical shape rather than hot formed. An electrical current is used to heat the edges of the strip for the fusion weld, while Continuous Weld pipe uses a flame. Revolving copper discs serve as electrodes and raise the temperature to about 2600°F for effective welding. As in Continuous Weld 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 Continuous Weld 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. Any ERW pipe used for the transmission of water, meets all American Water Works Association specifications.
ERW pipe is most commonly found with these specifications: A-252 Grade 1, 2, 3; API5L Grade A & B; and API5L X42 – X70. ERW pipe is available in lengths from single random to 80 feet. ERW pipe is available with square ends or beveled ends for welding, threaded, coupled and victaulic grooved. Surface finishes are available in black, bare, or with various protective coatings.
DSAW (Double Submerged Arc Welded)
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.
DSAW pipe is produced in sizes from 18″ through 72″ OD and wall thicknesses from .250″ through 1.5″.
Two different processes are used to manufacture DSAW pipe; the “Pyramid Rolls” method, and the “UOE” (U-ing, O-ing and Expanding) 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. The UOE method uses a “U” press, and “O″ press for forming the cylinder. The finishing and inspection processes are similar, and both methods use a flat steel plate as the raw material.
DSAW pipe may or may not be cold expanded. Cold expansion is a process where the pipe is expanded (up to 1.5%) to obtain its final OD dimension. In the process, a gain of yield strength results. Expansion is most often utilized in a UOE mill due to the need to recover yield strength lost during forming in the “O” 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, 5L X42 – 5L X80
DSAW pipe is normally produced in double random lengths with square ends or beveled ends. It is usually furnished bare but varnished pipe is also offered. A wide range of external coatings and internal linings are available with DSAW pipe.
Seamless pipe is produced domestically in sizes .54” OD through 26” OD. Seamless pipe is produced without a seam or weld in the circumference. Seamless pipe is produced using a variety of methods. To put it in the most simplistic terms; Seamless pipe is produced by piercing a solid billet of deoxidized and conditioned steel, which has been prepared and heated to the appropriate temperature. It is then processed through a series of mills where the pipe is finished to its prescribed dimensions. Seamless sizes over 14” OD are usually rotary rolled from 14” 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 X42 through X65.
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, 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. A “two-step” bevel is available for pipe that is 6”+ with at least a ¾” OD.
Spiral Weld Pipe, is a steel pipe that has a seam running its entire length in a spiral formation. 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, and dependable non-destructive testing methods, it is possible to produce large hot rolled coils of sufficient width 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 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.