ERW or Electric Resistance Welded pipes are hot rolled coils that get formed by electrically joining the two extremities of the coil. Manufacturers use copper electrodes to pass high-frequency current through the rolled coils.
This electricity flowing in opposite directions between two conductors cause to side intensively towards the edges, where resistance gets created. Once a certain temperature has been achieved, the pressure gets applied, making these seams join together.
What Are The Characteristic Features Of ERW Pipes
- ERW pipes have a longitudinal welded seam.
- These pipes are made by passing a high-frequency current through the steel coils and fusing the ends under high pressure.
- The outside diameter of an ERW pipe is ½ to 24 inches.
- ERW pipe wall thickness varies from 1.65 to 20mm
- The typical length is 3 to 12 m, but longer lengths are available on demand.
- ERW pipes can have plain, treaded, or beveled ends, as specified by the client.
- ERW pipes under specification ASTM A53 form the basis of most line pipes used in oil, gas, or vapor liquids.
Manufacturing Process Of ERW Pipes
Steel Coils form the base materials for making ERW pipes.
Step 1- Before they get fed to the welding mills, these metal strips are slit into specific widths and sizes to fit the pipe specifications.
Step 2- Once this splitting is done, the steel coils get uncoiled at the mouth of the ERW mill.
Step 3 - As they pass down the mill, these coils get turned into a tube-like shape with an unclosed longitudinal seam. ERW utilizes several techniques, including seam welding, flash welding, resistance projection welding, and more.
Step 4- The open seam coil is exposed to these welding treatments where the open edges get heated. This welding is done by passing high-frequency, low-voltage electricity through copper electrodes clamping onto the unfinished steel pipe.
Step 5- Flash welding is used in ERW pipe production because it does not require soldering material to join the two edges of the steel coil.
When this electrical heat gets applied to the coil, an arc discharge forms between the two edges; upon reaching a favorable temperature, the mills press the seams together, helping weld the product. As a result, this process produces a pipe that matches seamless pipes in look and strength.
However, manufacturers trim the welding beads using carbide tools even if other welding methods are used. The welded areas generate a lot of heat, so it is sometimes left to return to room temperature and cool in an air cooling bed.
Sometimes, this cooled tubing also enters a sizing roll to help the outside diameter meet the appropriate specification.
ERW vs. LSAW vs. Seamless
| ERW Pipes | LSAW Pipes | Seamless Pipes | |
| Production | ERW pipes are made by electrically fusing two steel coils together. | LSAW pipes are made by bending, cutting, and welding steel plates together. | Seamless pipes are made by perforating steel billets or ingots. |
|
Proportions |
ERW pipes have an even wall thickness as they are made from pre-cut coils. |
LSAW pipes have an even wall thickness as they are made from pre-cut plates. | Seamless pipes may have uneven proportions as they are formed from solid steel blocks. |
| Price | ERW pipe production is less complex and expensive as it uses stock steel coil as base material. | LSAW pipe production is less complex and expensive as it uses stock steel plates as base material. | Seamless pipes have a more extensive production process as steel billets take longer to shape. |
| Strength | Technological innovations like HFI make ERW pipes almost as durable as seamless pipes. | Since they have a welded area, LSAW pipes risk corrosion. | Seamless pipes have no welded area and are the strongest and most durable of pipes. |
ERW Pipes Specifications
ASTM A53 is mostly meant for carbon steel with nominal wall thickness; among this, Type E is the industry standard for ERW pipes.
Chemical Properties For ASTM A53 Type E
| ELEMENT | TYPE E GRADE A | TYPE E GRADE B |
| Carbon | 0.25 | 0.3 |
| Phosphorous | 0.05 | 0.05 |
| Sulfur | 0.05 | 0.05 |
| Nickel | 0.4 | 0.4 |
| Molybdenum | 0.15 | 0.15 |
| Vanadium | 0.08 | 0.08 |
| Copper | 0.4 | 0.4 |
| Manganese | 0.95 | 1.2 |
| Chromium | 0.4 | 0.4 |
Tensile Strengths
| GRADE | TENSILE STRENGTH (MIN) | YIELD STRENGTH (MIN) |
| Grade A | 48,000 psi | 30,000 psi |
| Grade B | 60,000 psi | 35,000 psi |
Other specifications for ERW pipes include API 5L for ERW oil and gas lines and API 5CT for casing and tubing.
Applications Of ERW Pipes
- The most common use of ERW pipes is as line pipes to carry crude oil, natural gas, and other material. They have a higher average diameter than seamless pipes and can meet high and low-pressure requirements, making them invaluable as transportation pipes.
- ERW pipes, especially of specification API 5CT, are used in casing and tubing
- ERW pipes may get used as structure tubes for wind power plants
- ERW pipes are used in the production industry as bearing sleeves, mechanical processing, processing machinery, and more
- ERW pipe uses include gas delivery, hydroelectric power fluid pipeline, and more.
- They also have uses in construction, underground pipelines, water transportation for groundwater, and hot water transport.
Advantages Of ERW Pipes
- ERW pipes have a high number of applications. Electrically welded API 5CT pipes are used in casing and tubing, while API 5L is used as line pipes.
- Though welded pipes are generally considered inferior to seamless pipes, technology like HFI and HFW has helped bridge this gap. These days ERW pipes are an effective substitute for seamless pipes in price and quality.
- The ERW production process is highly automated and uses minimal labor, resulting in a fast turnabout time. This quick product makes this an ideal product for larger production of small-diameter pipe sections.
- Though ERW pipes are almost as strong as seamless, they are comparatively cheaper and more accessible.
- Flash welding is a type of ERW that uses no fusion beads or other materials to join the two metal sheets. Instead, passing the high-frequency current through the sheet helps join the two ends together. This product is stronger than the average welded pipe.
- Post-production, ERW pipes have no welding lines or beads, making them seem almost seamless.
- Since the metal sheets get joined at high temperatures and pressure, the welded longitudinal area is sometimes stronger than the rest of the pipe surface.
- ERW production requires less equipment and labor, making it safer and more cost-efficient.