What is ERW steel pipe

What is ERW steel pipe?

ERW steel pipe” is a straight seam electric resistance welded pipe, abbreviated as ERW pipe, which is a round pipe welded by steel plates. It is used to transport vapor and liquid objects such as oil and natural gas, and can meet various requirements of high and low pressure. At present, it plays an important role in the world of transportation pipes.

1 ERW  2 Manufacturing Process
3 Standard  4 Quality inspection process

Electrical resistance welding

Electric resistance welding (ERW) refers to a group of welding processes such as spot and seam welding that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material combined with the time and the force used to hold the materials together during welding. Some factors influencing heat or welding temperatures are the proportions of the workpieces, the metal coating or the lack of coating, the electrode materials, electrode geometry, electrode pressing force, electrical current and length of welding time. Small pools of molten metal are formed at the point of most electrical resistance (the connecting or “faying” surfaces) as an electrical current (100–100,000 A) is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are limited to relatively thin materials and the equipment cost can be high (although in production situations the cost per weld may be low).

Electrical resistance welding - What is ERW steel pipe
ERW Production Lines

Electrical resistance welding will be welders parts formed pressed between two electrodes, and subjected to current, the resistor thermal effects generated by the current flowing through contact with the workpiece surface and the neighboring regions to be heated to melt the plastic state, so thatmetal-binding method. Resistance welding methods are mainly four kinds, namely, spot welding, seam welding, projection welding, butt welding.

erw pipe banner 1 - What is ERW steel pipe
ERW pipes means Electric Resistance Welded Pipes
ERW pipe hydraulic test - What is ERW steel pipe
ERW hydraulic test
Teleparty welding of ERW pipe - What is ERW steel pipe
Teleparty welding of ERW pipe
Off Line ERW Tube Inspection - What is ERW steel pipe
Off-Line ERW Tube Inspection
ERW cutting - What is ERW steel pipe
Teleparty welding of ERW pipe cutting

A plate rolled to become a pipe and welded using Electric Resistance Welding process.

Spot welding (Spot Welding)

Spot welding assembly into the lap joint, and pressed between two cylindrical electrodes, the resistance of hot-melt the base metal to form a solder joint resistance welding method. Spot welding is mainly used for sheet metal welding.

Seam welding (Seam Welding)

Seam welding and spot welding, just a rotating disc-shaped wheel electrode instead of the columnar electrode and the weldment assembly into a lap or butt joint, and placed between the electrodes of the two wheel roller pressure welding and rotation, continuous or intermittent transmission to form a continuous weld resistance welding method.

Projection welding

Projection welding is a variant form of spot welding; pre-bump in a workpiece, projection welding, once formed in the joints of one or more of the nugget.

Aeronautics and Astronautics, aerospace, electronics, automotive, household appliances, industrial development, resistance increasingly wide attention. Meanwhile, resistance welding quality also put forward higher requirements. The good news is that the development of microelectronics technology in China and high-power thyristor rectifier development, resistance welding technology to improve the conditions.

At present, China has produced the excellent performance of the secondary rectifier welder. integrated circuits and micro-computer control box for the new welder supporting the transformation of the old welder. Constant current, dynamic resistance, and thermal expansion of advanced closed-loop control technology has been in production application. All help to improve the welding quality, and expand its application areas.

ERW Pipe Manufacturing Process

(ERW) Electric resistance welded pipe is manufactured by cold-forming a sheet of steel into a cylindrical shape. 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.

Typical ERW Pipe Manufacturing Process

Manufacturing process generally involves the following stages in a step by step procedure.

erw pipe processes - What is ERW steel pipe

Slitting

HR Coils are slitted to pre-determined widths for each and every size of pipes

round form - What is ERW steel pipe

Round forming

Uncoiling, End Shearing And Welding

The slitted coil is uncoiled at the entry of ERW mill and the ends are sheared and welded one after another. This results in a single endless strip.

Forming

The slitted coils are initially formed into U shape and after that into a cylindrical shape with open edges utilizing a series of forming rolls.

erw welding - What is ERW steel pipe

Welding

Welding

In this stage, the open edges are heated to the forging temperature through high-frequency, low-voltage, high current and press welded by forge rolls making perfect and strong but weld without filler materials.

seam anbnealing - What is ERW steel pipe

Seam Annealing

The seam annealing process is dedicated to the normalizationof the Heat Affected Zone (HAZ), as the welding bonding line is modifiedfrom a metallurgic point of view and it can generate failure in flatteningand flaring tests.

De beading

In this stage, the weld flash on top and inside (if required) is trimmed out using the carbide tools.

Seam Annealing

If required, the welding portion and heat affected zone is put to normalizing and then are cooled down in a air cooling bed.

Sizing

After water quenching, slight reduction is applied to pipes with sizing rolls.

This results in producing desired accurate outside diameter.

pipe Beveld cut - What is ERW steel pipe
Pipe beveling

pipe cutting - What is ERW steel pipe

Pipe cutting

Cutting

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

End Facing And Bevelling

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

All these processes are continuous with automatic arrangements. These plain ended tubes further go for processing as per the customer requirements such as galvanizing, threading, black varnishing and more.

Pipe connection

connection pipe flanged all types - What is ERW steel pipe

Pipe connection is varied, the commonly used have Butt weld, Flanged, Threaded, Socket weld, Glued, Brazed and Grooved end.

Electric resistance welding at a glance

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

electric resistance welding at a glance hf induction welding - What is ERW steel pipe

Figure 2 / ObjectThe 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.

electric resistance welding at a glance hf contact welding description - What is ERW steel pipe

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).

electric resistance welding at a glance direct current weld - What is ERW steel pipe

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:

  • 3/8 to 2 in. uses two-roll units.
  • 1/2 to 3 1/2 in. uses three-roll units.
  • 2 to 10 in. uses four-roll units.
  • Larger than 10 in. uses five or more rolls.

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.

Galvanizing

Hot-dip galvanizing, it is at high temperatures the zinc ingots melt, being placed in the auxiliary material, then the metal structure is immersed in a zinc plating bath, so that the metal member attached to a layer on the zinc layer.
The hot galvanized advantage depend on its preservative ability, the better the adhesion and hardness of the galvanized layer.
Cold galvanizing is a zinc salt solution by electrolysis, to the plating on the coating, in general, which do not have heating, the amount of zinc rarely encountered humid environment is very easy to fall off. The cold galvanizing physical treatment, just in the surface brush a layer of zinc, zinc coating so easy to fall off the use of hot-dip galvanized construction.
Process of hot-dip galvanizing and cold galvanizing
Hot dip galvanized is immersed in liquid zinc dissolved workpiece degreasing, pickling, dipping, drying a certain period of time and put forward.
Cold galvanizing, also called electro-galvanized, is the use of electrolysis device to the workpiece into the composition of the zinc salt solution, after degreasing, pickling, and connecting the negative electrode of the electrolytic device; zinc plate placed at the opposite side of the workpiece is connected in the electrolytic device the positive electrode, the power is turned on, a current from the positive electrode to the negative directional movement, it will be deposited on the workpiece with a layer of zinc.
Appearance of hot-dip galvanizing and cold galvanizing
Cold galvanizing looks more smooth, bright, color passivation process plating layer is yellow-green in color, was colorful. Plating layer was bluish-white or white with white passivation process was green, white coating passivation process and the sun was significant Colorful angle. The complex workpiece angular edges parts prone to “electrical burning” from gloomy, the parts of the zinc layer thick. Yin corner site is easy to form a current dead undercurrent gray area and the area zinc layer is thinner. The workpiece overall zinc tumor, caking phenomenon.
Hot dip galvanized look a little rough compared to the electro-galvanized, silvery white, look prone process waterlines and a few drops of tumor is more obvious, especially in the one end of the workpiece. Hot dip galvanized zinc layer than a few times of the electro-galvanized thick corrosion protection is several times that of the electro-galvanized.

ERW pipe technical requirements

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

Technical requirements For oil and gas transport For low pressure fluid conveying 
Material Gr.b Gr.b
Pipe body diameter D<508mm, ±0.75%; D≥508mm, ±0.75% D≤168.3, ±1.0%;  168.3<D≤508,±0.75%;  
Wall thickness D<508mm,+15.0%,-12.5%; D≥508mm, +17.5%,-10% ±12.5%
Bending ≤0.2% ≤0.2%
Ovality D≥508mm,≤±1% ≤±0.75%
Bevel ≤1.59mm ≤5mm
Hydrostatic testing  100%  100% 
Nondestructive testing 100% non-destructive weld inspection Ultrasonic flaw detection is 100%

Note:

  • Yield strength of the N80 is higher than the J55 up to 173 ~ 206 MPa.
  • On the same area of the sample, the elongation of N80 is higher than J55.
  • Under the same size, the same sample orientation, the same minimum sample size, J55 grade couplings, coupling stock, coupling material, semi-finished and coupling attachment material can absorb lower than N80 steel grade.
  • The nondestructive testing methods of seamless pipe,coupling stock, welded tube with J55 and N80 is differeent.
  • J55 and N80 steel grade is not the same color: length greater than or equal 1.8m, J55 painted a bright green, N80 painted a red;
  • J55 chosen by the manufacturer, or organize according to the order specified length normalized (N), normalizing and tempering (N & T) or quenching and tempering (Q & T). N80 is a whole, full-length heat treatment is mandatory. By the manufacturer selected for normalizing (N) or normalizing and tempering (N & T) + quenching (Q).

Standard:

  1. API 5L
  2. ASTM A53 B
  3. ASTM A178
  4. ASTM A500/501
  5. ASTM A691
  6. ASTM A252
  7. ASTM A672
  8. EN 10217

API 5L

Chemical Analysis and Mechanical Properties
Standard Class Grade Chemical Analysis(%) Mechanical Properties(min)(Mpa)
C Mn P S Tensile Strength Yield Strength
API 5L PSL1 B 0.26 1.20 0.030 0.030 414 241
X42 0.26 1.30 0.030 0.030 414 290
X46 0.26 1.40 0.030 0.030 434 317
X52 0.26 1.40 0.030 0.030 455 359
X56 0.26 1.40 0.030 0.030 490 386
X60 0.26 1.40 0.030 0.030 517 414
X65 0.26 1.45 0.030 0.030 531 448
X70 0.26 1.65 0.030 0.030 565 483
PSL2 B 0.22 1.20 0.025 0.015 414 241
X42 0.22 1.30 0.025 0.015 414 290
X46 0.22 1.40 0.025 0.015 434 317
X52 0.22 1.40 0.025 0.015 455 359
X56 0.22 1.40 0.025 0.015 490 386
X60 0.22 1.40 0.025 0.015 517 414
X65 0.22 1.45 0.025 0.015 531 448
X70 0.22 1.65 0.025 0.015 565 483
X80 0.22 1.85 0.025 0.015 621 552

Tolerance of outside diameter

 Standard  Out Diameter  Tolerance of Pipe End  Tolerance of Pipe Body
 API 5L  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

 Standard  Grade  Out Diameter  Wall Thickness
API 5L  /  219.1-457  +15%, -12.5%
 B  508-610  +17.5%, -12.5% 
 X42-X80  508-610  +19.5%, -8%

ASTM A53 B

Chemical of ASTM A53 B ERW Steel Pipe

Type

Carbon

max. %

Manganese

max. %   

Phosphorous

max. %

Sulfur

max. %

Copper

max. %

Nickel

max. %

Chromium

max. %

Molybdenum

max. %

Grade A Grade B Grade A Grade B Grade A Grade B Grade A Grade B Grade A Grade B Grade A Grade B Grade A Grade B Grade A Grade B
Type E 
(electric-resistance welded)
0.25 0.30 0.95 1.2

0.05

0.05 0.045 0.045 0.40 0.40 0.40 0.40 0.15 0.15 0.08 0.08

Tensile of ASTM A53 B ERW Steel Pipe:

Tensile


Electric-resistance-welded

Grade A Grade B

Tensile Strength

 min. psi

48,000 45,000

Yield Strength

 min. psi

30,000 25,000

Specification of ASTM A53 B ERW Steel Pipe

Wall Thickness

Out Diameter

Inch

mm

inch

mm

inch

mm

inch

mm

inch

mm

inch

mm

inch

mm

inch

mm

inch

mm

inch

mm

8 5/8

219.1

10 3/4

273.1

12 3/4

325.0

14

355.6

16

406.4

18

457.7

20

508.0

24

610

24 4/5

630.0

0.157

4.0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.197

5.0

 

 

 

 

 

 

 

 

 

 

0.236

6.0

 

 

 

 

 

 

0.276

7.0

 

 

 

 

 

0.315

8.0

 

 

0.354

9.0

 

 

0.394

10.0

0.433

11.0

0.492

12.5

0.551

14.0

 

 

 

 

0.630

16.0

 

 

 

 

0.689

17.5

 

 

 

 

 

 

 

 

0.748

19.0

 

 

 

 

 

 

 

 

 

 

0.787

20.0

 

 

 

 

 

 

 

 

 

 

 

 

Quality inspection process of erw steel pipe

Quality inspection process of erw steel pipe consists of online non-destructive testing, metallographic examination, flattening and flaring destructive tests and hydraulic tests. Assessment process:
1, Online non-destructive testing
The detection station’s detection arm is rotated and placed in the longitudinal welded pipe production line. The position of the weld is observed through the camera. The position of the probe is adjusted by using the operating rod, so that the weld overlaps with the laser, and the parameters are saved. Enter the coil number via the DATASERVR and DACQ computers. Observe the waveform display of the flaw detection interface. When the waveform exceeds the alarm line, compare the thickness measurement information to determine whether it is a defect wave or an interference wave signal, and visually inspect the pipe to see if the waveform exceeds the alarm line. If the alarm line exceeds the alarm line, an alarm will be given. Shut down in time and readjust welding parameters.
2. Metallographic examination

  • (1) Metallographic microstructure of the weld. Generally, after the heat treatment of the weld seam, it is used to judge whether the heat-affected zone coarse structure is completely eliminated and whether it is basically the same with the base material, whether there is inclusion in the weld fusion line. In general, the welds are free of inclusions, microcracks, and organized structures, indicating a welded grid.
  • (2) Metal streamline morphology. In high-frequency welding, the proximity effect and the skin effect make the strip edge in a molten and semi-molten state. Under the pressure of the squeezing roller, the weld metal flows inwards and outwards, and the parent metal flow line on both sides of the weld is raised to form a clip. Angle, called the streamline angle α, generally determines the weld as qualified at 40° to 70°; beyond this range, the welding process parameters need to be adjusted in time.

3, Destructive test

  • (1) Flattening test. Cut about 100mm welded pipe and place it under the hydraulic machine. The weld position is perpendicular to the direction of the hydraulic press. Start the hydraulic pressure. Slowly press down the welded pipe and press it to 3/4 of the diameter to see if the weld cracks. If there is no crack, weld the grid; if there is cracking, adjust the welding process parameters in time.
  • (2) Flaring test. About 100mm welded pipe was placed on a conical top core; the conical top core was placed under a hydraulic press, the hydraulic pressure was started, and the welded pipe was slowly pressed down. When the flaring reached 8%, it was checked whether the weld cracked. If there is no crack, weld the grid; if there is cracking, adjust the welding process parameters in time.

4, Hydraulic test
In the hydraulic test, flanges are used to seal both ends of the welded pipe behind the welding flange, and then the pipe is filled with water and pressure is gradually applied to the pressure required by the relevant standards. After a certain period of time, the pipe welding is visually measured. There is no leakage at the seam. If there is no leakage, weld the grid; if there is leakage, timely adjust the welding process parameters. In the hydraulic test, there was no leakage at the weld seam and the weld grid was welded. This is also the last step in the quality inspection of the welded pipe.

Source: China ERW Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@pipelinedubai.com

Please notice that you might be interested in the other technical articles we’ve published:

References:

  • https://www.yaang.com
  • https://en.wikipedia.org/wiki/Electric_resistance_welding

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