Overview of ERW Steel Pipe

ERW steel pipe "refers to straight seam resistance welded pipe, also known as Electric Resistance Welding, abbreviated as ERW. It occupies an important position in the field of transportation pipes worldwide. It is a metal pipe made by heating the joints of steel strips with high-frequency current and performing resistance welding.

Difference from seamless steel pipe

The biggest difference between ERW steel pipes and seamless steel pipes is that ERW has a single weld seam, which is also the key to the quality of ERW steel pipes.

Seamless processing

Geometry seamless

Remove internal and external burrs from the ERW steel pipe. Due to the continuous improvement and perfection of the structure and cutting tools of the internal burr removal system, the removal of internal burrs in large and medium-sized steel pipes has been well processed, and the internal burrs can be controlled at around -0.2mm~0.5mm.

Physical seamless integration

The difference between the metallographic structure inside the weld and the base metal can lead to a decrease in the mechanical properties of the weld area. Physical seamless welding requires measures to make it uniform and consistent. The high-frequency welding process of ERW steel pipes causes a temperature distribution gradient near the edge of the billet, and forms characteristic areas such as melting zone, semi melting zone, overheated structure, normalizing zone, incomplete normalizing zone, and tempering zone. The microstructure in the overheated zone undergoes rapid growth of austenite grains due to welding temperatures above 1000 ℃. Under cooling conditions, a hard and brittle coarse grain phase is formed. In addition, the presence of temperature gradients can generate welding stresses, resulting in lower mechanical properties in the weld area compared to the base metal. Physical seamless welding is achieved through local conventional heat treatment of the weld seam, which uses a medium frequency induction heating device to heat the weld area to AC3 (927 ℃), and then undergoes an air cooling process with a length of 60m and a speed of 20m/min, followed by water cooling if necessary. This method achieves the goal of eliminating stress, softening and refining microstructure, and improving the comprehensive mechanical properties of the welding heat affected zone. At present, advanced ERW units in the world have widely adopted this method to treat welds. High quality ERW steel pipes not only cannot distinguish welds, but also have a weld coefficient of 1, achieving matching between the microstructure of the weld area and the base material.

Production process

Raw material preparation: Select high-quality steel plates and cut and straighten them according to specifications.

Roll forming: Roll the steel plate into a circle and weld it to form a pipe blank.

High frequency welding: using high-frequency current to heat the billet, form a molten pool, and perform welding.

Dimensional correction: Perform dimensional correction on the welded steel pipe to ensure that its dimensions meet the requirements.

Surface treatment: Rust removal, painting and other surface treatments are carried out on steel pipes to protect their surface.

characteristic

advantage

High strength and toughness: Made of high-quality steel, it has high strength and toughness, can withstand large pressure and impact, and can maintain good performance under various harsh conditions, such as high temperature, low temperature, corrosion, etc.

Uniform wall thickness: Due to the use of hot-rolled coils as raw materials, the uniform wall thickness can be controlled at around ± 0.2mm.

High dimensional accuracy: The production process adopts precision control technology to ensure the dimensional accuracy and surface smoothness of the pipes, which enables the ERW steel pipes to be better connected to other components during use, improving overall installation efficiency and reliability.

Delivery standard specification: The two ends of the steel pipe shall be repaired and beveled according to the American APl standard or GB/T9711.1 standard, and delivered in fixed length.

Production advantages: Resistance welding has the characteristics of high production efficiency, low cost, material saving, and easy automation.

Environmental advantages: Production and application are conducive to environmental protection and reduce the impact on the environment.

limitation

There is a weld seam, and quality control of the weld seam area is crucial. If not handled properly, the mechanical properties of the weld seam area may be lower than those of the base metal.

application area 

Construction industry: widely used in building structures such as steel frame structures, reinforced concrete structures, steel bridges, etc.

Oil and natural gas: used as oil and gas transmission pipelines, suitable for underground or offshore pipelines due to its corrosion resistance. In recent years, various natural gas pipeline projects and gas companies have widely adopted ERW steel pipes as the main steel pipes for urban pipelines.

Automobile manufacturing: used as important components such as automobile chassis, frame, doors, wheels, etc. Its strength and lightweight characteristics are widely used in the automotive industry.

New energy: Applied in the field of new energy such as wind turbine towers and solar brackets, its high strength, lightweight, and corrosion resistance make it an ideal material choice.

Quality requirements and testing methods

quality requirement

Dimensional accuracy: Strict requirements are required to ensure its stability and reliability in application.

Uniformity of wall thickness: It is an important indicator of the quality of ERW steel pipes, which directly affects the strength and durability of the pipes.

Surface quality: The surface should be smooth, clean, and free of defects such as cracks, pores, and slag inclusions to ensure its good appearance and corrosion resistance.

Mechanical properties: Tensile strength, yield strength, elongation and other mechanical properties should meet the design requirements to ensure their safety and reliability during use.

test method 

Dimensional inspection: Use calipers or vernier calipers to measure the outer diameter and wall thickness of steel pipes to ensure compliance with standard requirements.

Appearance inspection: Check the surface of the steel pipe for defects such as cracks, dents, scratches, etc., to ensure a smooth and flat surface.

Mechanical performance testing: Conduct tensile tests, bending tests, impact tests, etc. to verify the strength, toughness, and impact resistance of steel pipes.

Chemical composition testing: By using spectroscopic analyzers and other equipment, the chemical composition of steel pipes is tested to ensure compliance with standard requirements.

Quality control, transportation, storage, and installation precautions

quality control

Raw material quality control: Strictly control the quality of raw materials to ensure that steel meets standards.

Welding quality control: Adopting advanced welding processes and equipment to ensure welding quality.

Size control: Strictly control the size of steel pipes to ensure dimensional accuracy.

Surface quality control: Advanced surface treatment processes are used to ensure surface quality.

Transportation and Storage

Safe transportation: Choose appropriate transportation methods and vehicles to prevent damage to steel pipes during transportation.

Moisture proof measures: Use moisture-proof materials for packaging to prevent steel pipes from getting damp and affecting their performance.

Regular inspection: Regularly inspect the storage environment of steel pipes and promptly deal with corroded or damaged steel pipes. It should be stored in a dry and ventilated place, avoiding direct sunlight and rainwater immersion. Regularly check the surface of the steel pipe for corrosion or damage.

Installation precautions

Surface treatment: Before installation, clean the surface of the steel pipe to remove dirt, grease, and rust.

Pipe fitting selection: Choose fittings that match the size and specifications of the steel pipe to ensure a secure connection and prevent leakage. Use high-quality fittings to improve installation quality.

Welding process: Select appropriate welding methods and parameters based on the steel pipe material and specifications to ensure welding quality and prevent welding defects. After welding is completed, necessary inspections and tests shall be carried out.