The manufacturing process of ERW pipes incorporates High-Frequency Welding (HFW), which encompasses low, medium, and high-frequency welding methods. HFW is specifically designed for high-frequency electric resistance welding. Notably, EFW represents a type of ERW process tailored for ordinary and thin-wall thickness steel pipes.
- ERW pipe: Electric Resistance Welded Pipe
- HFW pipe: High Frequency Welding pipe
What exactly is ERW steel pipe?
ERW steel pipe is crafted through Electric Resistance Welding, utilizing low or high frequency resistances. The welding seam runs longitudinally. In the ERW pipe welding process, electric current generates heat as it flows through the contact surface of the welding area. This heat causes the edges of the steel to reach a temperature where they can bond together. Simultaneously, under applied pressure, the edges of the pipe billet steel melt and fuse together.
ERW pipes have a maximum outer diameter of 24 inches (609mm). For larger dimensions, pipes will be produced using the SAW method.
What standards of pipes can be produced using the ERW manufacturing process?
The range of pipes that can be manufactured using the ERW process is extensive. Below, we outline the most common standards for pipelines:
Stainless Steel ERW Pipe/Tube Standards and Specifications:
- ASTM A269 stainless tube
- ASTM A312 stainless pipe
- ASTM A270 sanitary tubing
- ASTM A790 ferritic/austenitic/duplex stainless pipe
Carbon Steel Pipe in ERW:
- ASTM A53 Grade B and A (including Galvanized)
- ASTM A252 pile pipe
- ASTM A500 structural tubing
- EN 10219 S275, S355 pipe
- ASTM A134 and ASTM A135 pipe
API ERW Line Pipe:
- API 5L B to X70 PSL1 (PSL2 is manufactured using the HFW process)
- API 5CT J55/K55, N80 casing and tubing
And more.
Application and Usage of ERW Steel Pipe: ERW steel pipe is utilized for transporting gas and liquid objects such as oil and gas, meeting both low and high-pressure requirements. In recent years, with advancements in ERW technology, its usage has expanded into various sectors including the oil and gas fields, and the automobile industry.
Benefits of ERW Pipes Efficient, cost-effective, material-efficient, easily automated.
What is HFW steel pipe?
It's important to note that HFW pipe falls under the category of ERW pipes.
High Frequency Welding (HFW) steel pipe is produced through a welding process with a current frequency equal to or greater than 70 kHz. During high-frequency current welding, resistance generates heat in the contacted objects, heating the surface to a plastic state. This allows for the forging, with or without, to achieve steel combination. HFW relies on solid resistance heat energy. The high-frequency current passing through the metal conductor creates two distinctive effects: skin effect and proximity effect. The HFW process utilizes the skin effect to concentrate on the steel object's surface and the proximity effect to control the position and power of the high-frequency electric current flow path. Due to its rapid speed, the contacted plate edges can be quickly heated and melted, then extruded through the docking process.
Benefits of HFW Pipes
During the welding process, HFW steel pipes eliminate the need for additional filler metal, resulting in rapid welding speed and enhanced production efficiency. Widely utilized in oil and gas transportation, oil well pipelines, structural building projects, and various mechanical applications, HFW pipes offer notable advantages. However, their quality is influenced by multiple factors, including raw materials and production processes, posing challenges in quality control. Continuous enhancements are essential to optimize yield and welding processes.
Differences between ERW and HFW steel pipes
To understand the disparities between ERW and HFW welding processes:
ERW welding involves generating heat by resisting the current flow passing through joined metals. Thus, a significant current is required to electrify the entire surface of the steel plate or coil to the length of welding. In the ERW welding process, the electric current passing through the entire conductor operates at 50/60 Hz.
On the other hand, HFW welding differs from the high-frequency process, as only a section of the steel metals is heated by the induction of electric coil. High-frequency is generated by either AC or DC current. In these instances, constant current welding generators and constant voltage high-frequency welding generators are utilized.
Constant current welding machines produce power in the range of 100-800 kHz. In earlier processes, the conversion of 60 Hz AC current to HF was achieved using triode and tank circuits. Modern welding machines employ metal oxide silicon, field-effect transistors, typically associated with parallel resonant circuits. The constant voltage version generators utilize insulated gate bipolar transistors designed to power around 2000 kW with frequency ranges of 100-600 kHz.
There are two notable distinctions of HF current compared to 60 Hz line current:
- While the 60 Hz line frequency current flows through the entire conductor, HF current only flows on the surface, hence the "skin effect."
- When two conductors carrying HF current are placed close to one another, the current concentrates on the adjacent surfaces, known as the "proximity effect."
HFW current distribution: The current flows primarily in the surface of the metal or conductor. Both conductors are positioned in close proximity, with most of the HF current flowing on the adjacent sides of the conductors.
HFW is mandated in API 5L PSL2 ERW steel pipes As per the API 5L and ISO 3183 specifications, HFW welding is a mandatory requirement for PSL 2 pipes in the welded process for ERW steel pipes. This is an enhancement from inherent issues such as hardness, lack of fusion, and susceptibility to stress corrosion cracking (SCC).
ERW steel pipes include HFW steel pipes ERW is a general designation for resistance welded steel pipes, which can be categorized into two types: alternating current welding (AC) and direct current welding (DC). Depending on the frequency, AC welding can be further divided into low frequency welding, intermediate frequency welding, ultra-frequency welding, and high-frequency welding. High-frequency welding (HFW) is predominantly used in ordinary or thin-wall steel pipes and encompasses contact welding and induction welding. Direct current welding is typically employed for small-caliber steel tubes. In essence, HFW is one of the ERW production methods, adopting the high-frequency welding process. Therefore, ERW steel pipes encompass HFW steel pipes.
