what is the difference between erw and seamless pipes

The biggest difference between ERW steel pipe and seamless steel pipe is that ERW has weld seam, which is the key to the quality of ERW steel pipe. The production technology and equipment of modern ERW steel pipes, due to the unremitting efforts of many years in the world, especially in the United States, have made seamless ERW steel pipes achieve relatively satisfactory results.

The difference between ERW steel pipe and seamless steel pipe
Some people divide the seamlessness of ERW steel pipes into geometric seamlessness and physical seamlessness. Geometric seamless is designed to eliminate internal and external burrs from ERW steel pipes. The removal of internal burrs in large and medium diameter steel pipes is better handled due to the continuous improvement and improvement of the structure of internal burr removal systems and cutters. Internal burr can be controlled between -0.2mm to 0.5mm.

Physically seamless means that there is a difference between the metallographic structure inside the weld and the base metal, which leads to a decrease in the mechanical properties of the weld area, requiring measures to be uniform. The high-frequency welding heat treatment of ERW steel pipes results in a temperature distribution gradient near the edge of the tube blank, and forms characteristic areas such as melting zone, semi-melting zone, superheated structure, normalizing zone, incomplete normalizing zone and tempering zone. Since the welding temperature is higher than 1000°C, the microstructure of the superheated zone has obvious austenite grain growth, and a hard and brittle coarse-grained phase is formed under cooling conditions. In addition, the presence of temperature gradients can create welding stress. In this way, the mechanical properties of the resulting weld zone are lower than in the case of the base material. The physical seamlessness is achieved by heating the weld area to AC3 through the traditional local heat treatment process of the weld using a medium frequency induction heating unit. (927°C), followed by air cooling at a length of 60 m and a speed of 20 m/min and, if necessary, water cooling. The use of this method achieves the purpose of relieving stress, softening and refining the structure, and improving the comprehensive mechanical properties of the welding heat-affected zone. So far, the world’s advanced ERW devices generally use this method to process welds, and have achieved good results. High-quality ERW steel pipes not only fail to identify welds, but also have a weld coefficient of 1, which matches the structure of the weld zone to the base metal.

Since the ERW steel pipe is made of hot-rolled coil, the wall thickness can be uniformly controlled at about ±0.2mm. Both ends of the steel pipe meet the American APl standard or GB/T9711.1 standard, the slope is repaired, and the fixed length is delivered. In recent years, various natural gas pipeline network projects and natural gas companies have widely adopted ERW steel pipes as the main steel pipes for urban pipeline networks.