Electric Resistance Welded Pipe

ERW (Electrical Resistance Welding) pipes are manufactured by cold forming of steel coil into a round cylindrical shape are used in various engineering purposes.

ERW steel pipe is formed by rolling plate and welding the seam.

Features of ERW pipe

Low cost: the low raw material cost and manufacturing cost make it prices more competitive than longitudinal seam submerged-arc welded pipes and seamless pipes.

High Weld Seam Security: As a result of special welding method of melting parent metal together, without filler metal, the weld property is better than submerged-arc welded pipes; and the weld seam is much shorter than spiral seam welded pipes, the seam security is greatly improved.

Wide Range: ERW pipes can be applied with a wide range of thickness / diameter ratio, covering hundreds of specifications.

Electric resistance welding at a glance

This article provides an overview of electric resistance welding (ERW). It dicusses high-frequency ERW (contact and induction) and rotary wheel contact welding (AC, DC, and square wave). It describes the differences among the processes, as well as the power supplies and weld rolls.

Index:
Process, power supply, and weld roll basics
Several electric resistance welding (ERW) processes are available for tube and pipe production. While each process has different characteristics, all ERW processes have one thing in common–all of them produce a forged weld.

A forged weld is created by applying a combination of heat and pressure, or forging force, to the weld zone. A successful forged weld uses the optimum amount of heat, which is normally slightly less than the melting point of the material, and a nearly simultaneous application of circumferential pressure to the section, which forces the heated edges together (see Figure 1).

As the name implies, the heat generated by the weld power is a result of the material's resistance to the flow of electrical current. The pressure comes from rolls that squeeze the tube into its finished shape.

The two main types of ERW are high-frequency (HF) and rotary contact wheel.
The Basics of HF Welding

Induction welding
Figure 2 / Object

The two main aspects of HF welding are processes and power supplies. Each of these can be broken down further into subcategories. Processes. The two HF welding processes are HF contact and HF induction. In both processes, the equipment that provides the electrical current is independent from the equipment that supplies the forge pressure. Also, both HF methods can employ impeders, which are soft magnetic components located inside the tube that help to focus the weld current in the strip edges.

Contact welding description
Figure 3 / Object

HF Induction Welding. In the case of HF induction welding, the weld current is transmitted to the material through a work coil in front of the weld point (see Figure 2). The work coil does not contact the tube--the electrical current is induced into the material through magnetic fields that surround the tube. HF induction welding eliminates contact marks and reduces the setup required when changing tube size. It also requires less maintenance than contact welding.

It is estimated that 90 percent of tube mills in North America use HF induction welding.


HF Contact Welding. HF contact welding transfers weld current to the material through contacts that ride on the strip (see Figure 3). The weld power is applied directly to the tube, which makes this process more electrically efficient than HF induction welding. Because it is more efficient, it is well-suited to heavy-wall and large-diameter tube production.

Power Supplies. HF welding machines also are classified by how they generate power. The two types are vacuum tube and solid-state. The vacuum tube type is the traditional power supply. Since their introduction in the early '90s, however, solid-state units have quickly gained prominence in the industry. It is estimated that between 500 and 600 of each type are operating in North America.


The Basics of Rotary Contact Wheel Welding
In rotary contact wheel welding, the electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies some of the forge pressure necessary for the welding process.

The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges.

AC Rotary Contact Wheel Welding. In an AC rotary contact wheel welding machine, the current is transferred through the brushes to the rotating shaft, which has a transformer mounted on it. The transformer reduces the voltage and increases the current, making it suitable for welding. The two legs of the transformer's output circuit are connected to the two halves of the rotating contact wheel, which are insulated from each other. The strip completes the circuit by acting as a conductor between the two halves of the wheel.

Traditional rotary contact wheel welders used 60-hertz AC, or common line current. A drawback to this system is that the current--and therefore the weld heat--rises and falls, limiting the speed at which the tube can be welded. An AC sine wave reaches its maximum amplitude briefly, producing weld heat that varies just as the sine wave does (see Figure 4).

Direct current weld
Figure 5 / Object

To help even out the heat variation, motor generator sets were introduced to create AC at higher frequencies. Some of the frequencies used were 180, 360, 480, and 960 Hz. A few solid-state units also were produced to generate higher-frequency currents. An AC sine wave at 960 Hz reaches its maximum amplitude 1,920 times per second, as opposed to 120 times per second with a 60-Hz signal. The 960-Hz sine wave produces heat with a much more consistent temperature.

DC Rotary Contact Wheel Welding. The next step in rotary contact wheel welding was the DC power supply. The power produced has a nearly constant amplitude. Although this solves the problem of varying heat, a major drawback is that higher maintenance costs are associated with this type of welding machine.

Because it is not possible to change the voltage of DC with a transformer, it is necessary to transmit the high-amperage, low-voltage weld current into the shaft through a large number of brushes (92 for DC versus 8 for AC) with a high current density. Transmitting high-amperage, low-voltage current produces excess (waste) heat that causes heavy wear, resulting in the high maintenance costs mentioned previously.

Square Wave Rotary Contact Wheel Welding. The latest step in the evolution of rotary contact wheel welding is the square wave power supply. This method combines the consistent weld heat of DC with the lower maintenance associated with AC units (see Figure 5). While rotary contact weld methods preceded the more commonly used HF welding processes, they still have a vital role in specialty welding applications. Rotary contact welding is useful for applications that cannot accommodate an impeder on the ID of the tube. Examples of this are small-diameter refrigeration-grade tube and tube that is painted on the ID immediately after the welding process.


How Many Roll Units Are Needed?

The types of weld pressure rolls, or squeeze boxes as they sometimes are called, that apply the pressure required for the weld are as varied as the welding units used to supply the heat. Squeeze boxes for rotary contact wheel welding typically have two or three roll units, with the contact wheel serving as one of the rolls.

The number of rolls in the weld squeeze box is proportionate to the size and shape of the product being welded. There are no hard and fast rules; however, common guidelines for round tube or pipe size ranges are as follows:

Today, much more so than in the past, many shapes--square, rectangular, hexagonal--are welded in the finished shape rather than being reshaped after being welded round. The weld boxes used for the shapes are custom-designed for each application and usually have no more than five rolls.

Beveld
End Facing And Bevelling

This is usually stage, where the pipes ends are faced and bevelled by the end facer.

Cutting
In cutting stage, the pipes are cut to required lengths by flying cut off disc/saw cutter.

General Standard

Standard Specification
ASTM A53 Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless
API 5L Specification for Line Pipe(Two levels PSL 1 and PSL 2 of seamless and welded steel pipes for use in pipeline transportation systems in the petroleum and natural gas industries.)
A252 Standard Specification for Welded and Seamless Steel Pipe Piles
A500 Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes
A135 Standard Specification for Electric-Resistance-Welded Steel Pipe
A178 Standard Specification for Electric-Resistance-Welded Carbon Steel and Carbon-Manganese Steel Boiler and Superheater Tubes

Dimensional tolerance of ERW steel pipe

Tolerance of outside diameter
 Out Diameter  Tolerance of Pipe End  Tolerance of Pipe Body
 219.1-273.1  +1.6mm, -0.4mm   ±0.75% 
 274.0-320  +2.4mm, -0.8mm  ±0.75% 
 323.9-457  +2.4mm, -0.8mm  ±0.75% 
 508  +2.4mm, -0.8mm  ±0.75% 
 559-610  +2.4mm, -0.8mm  ±0.75% 
Tolerance of wall thickness
 Grade  Out Diameter  Wall Thickness
 /  219.1-457  +15%, -12.5%
 B  508-610  +17.5%, -12.5% 
 X42-X80  508-610  +19.5%, -8%

DOWNLOAD STANDARD

Even welding and smooth weld line, can be substitute for seamless tube after drawing and cold rolling.

A 178/A 178M – 02

Standard Specification for Electric-Resistance-Welded Carbon Steel, Carbon Manganese Steel Boiler, Superheater Tubes

SA-450/SA-450M

SPECIFICATION FOR GENERAL REQUIREMENTS FOR CARBON, FERRITIC ALLOY, AND AUSTENITIC ALLOY ...

The manufacture of electric resistance welded pipe

While manufacturing ERW steel pipes, only high-quality, continuous-cast, fully killed, control-rolled, fine-grain, low-carbon steel is used.

ERW pipe FAQs

ERW steel pipes and tubes are used in various engineering purposes, fencing, scaffolding, line pipes etc.

The surface condition of steel pipe is known as the environment that this is through the steel pipe coating with the surrounding soil insulation, pipe surface condition is different from the four weeks the soil.

The alloy content of the coil is often lower than similar grades of steel plate, improving the weldability of the spiral welded pipe. Due to the rolling direction of spiral welded pipe coil is not perpendicular to the pipe axis direction, the crack resistance of the spiral welded pipe materials.

Electric resistance welded

Current is then passed between the two edges of the steel to heat the steel to a point at which the edges are forced together to form a bond without the use of welding filler material. Initially this manufacturing process used low frequency A.C. current to heat the edges. This low frequency process was used from the 1920’s until 1970. In 1970, the low frequency process was superseded by a high frequency ERW process which produced a higher quality weld.

Steel pipe for pipe technology, can be divided into (SML), mainly as the Oilfield internal transportation pipeline and small-diameter high-pressure natural gas pipeline, used for a small number of long-distance gas pipeline, the vast majority of long-distance pipeline with Direct seam high frequency (ERW), spiral submerged arc (SSAW), LSAW three (LSAW).

A continuous helical fin is attached to the base tube by high frequency electric resistance welding in order to give an efficient and thermally reliable bond. Fins can be either solid or serrated (segmented). The weld produced in this process is a true forge, blacksmith weld. This type of weld is comprised of a fusion between two portions of parent metal without the introduction of a filler material. The weld is simply produced by heating the interfaces to be joined to a plastic state and applying pressure.

Used in boilers, furnaces and fired heaters for efficient heat recovery.

ERW steel pipes and tubes are used in various engineering purposes, fencing, scaffolding, line pipes etc.

The residual defects in erw steel pipe ultrasonic testing is an important reason for failure of the weld, causing defects missed is inappropriate due to a probe parameter selection, disturbing wave effects and burr flaw echo echo does not distinguish between such a variety of factors.

The residual defects in erw steel pipe ultrasonic testing is an important reason for failure of the weld, causing defects missed is inappropriate due to a probe parameter selection, disturbing wave effects and burr flaw echo echo does not distinguish between such a variety of factors.

Scrape the inside welds very smooth burr, weld and base metal transition very smooth. Usually a steel pipe wall thickness is 11.9mm, a thickness range of extrusion welds typically range from about 25mm to either side of each weld, the weld portion after the removal of burr than other parts of the base material thickness of about 10%.

ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes.

Straight seam welded steel pipe, according to welding process can be divided into high frequency resistance welding and submerged arc welding, longitudinal submerged arc welded is short for SAWL, high-frequency straight seam resistance welding is short for ERW.

Resistance welding is short of ERW steel pipe with number of advantages, such as high productivity, low cost, good dimensional accuracy, beautiful appearance. However, in the past, due to the poor reliability of the weld, great limitations on the use. The proportion of small pipe production.

Analysis of the frequency of inclusions in steel production, the pre-arc fusion inadequate inadequate edge fusion, central fusion deficiencies, stick welding, casting welding, porosity, skip welding and other welding defects nine common causes and preventive measures.

ERW pipe issues and defects is related to raw materials, production methods, process conditions, equipment status and personnel. Product defects that appear in the production process by the above factors and constraints.

Also known as the "skin effect," When an alternating current through a conductor, due to induction effect caused by the larger cross section of the conductor current distribution is uneven, the closer the conductor surface current density.

High-frequency electric resistance welding (ERW) steel pipe production, internal weld surface treatments are generally incomplete curettage (left weld reinforcement) and complete curettage (scraping will form the inner surface of the groove) in two ways, and the results were not ideal, will affect the overall performance of the steel pipe. Taking into account the thickness of ERW pipe welds, strength and reliability of ultrasonic testing, squeeze through thick welds - calibrating processing, optimized contour shape welds to improve the overall performance of ERW pipe.

What is Welding?

Argon welding
Argon welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces.

Weled steel pipe specification, Standard and identification

Welded steel pipe (steel 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.