Some people coming into contact with steel tube for the first time don't know the difference between seamless pipe and ERW steel pipe. Actually, the biggest difference between ERW steel pipe and seamless pipe is there is a welding seam on ERW steel pipe, this is also the key to the quality of ERW steel pipe. Modern production process and equipment of ERW steel pipe, in the international community, due to years of unremitting efforts by many countries, especially the United States, making the ERW steel pipe seamless has been more satisfied with the solution.
ERW steel pipe seamless was divided into geometric seamless and physical seamless by some people:
About geometric seamless, its definition is removing the burr of ERW steel pipe on the inside and outside. As the continuous improvement of the structure of the inner burr removal system and cutting tool, the clearance of the burrs in the large and medium diameter pipes has been well handled. Burr can be controlled in the -0.2mm ~ O.5mm or so.
Physical seamless means that the difference between the metallographic structure inside the weld and the base metal results in a decrease in the mechanical properties of the weld area. It is necessary to take measures to make it uniform and consistent. The high-frequency welding process of ERW steel pipe, resulted in the temperature distribution gradient near the edge of the tube, and formed melting zone, semi-melting zone, superheated organization, normalized area, incomplete normalized area, tempered area and other characteristic areas. Due to the welding temperature in the superheated organization is above 1000 ℃, the austenite grain grows rapidly, the hard and brittle coarse crystalline phase is formed under cooling conditions. In addition, the existence of temperature gradient will produce welding stress. In this way, the situation that the weld area of mechanical properties is lower than the base metal situation will be formed. Physical seamless is the local conventional heat treatment process of weld (that is using medium frequency induction heating device to heat weld region to AC3 (927 ℃)), and then proceed the 60m length, the speed of 20m / min air cooling process.If it is necessary, the water cooling will be carried. The use of this method has achieved the purpose of eliminating stress, softening and refining the structure, and improving the comprehensive mechanical properties of the heat affected zone. So far, this method has been widely used by the world's most advanced ERW unit to deal with the weld, and that has achieved good results. The high-quality ERW steel pipe not only can not discern the weld, and the weld coefficient can reach to 1, achieves the weld area organization and base metal match.
Due to use hot-rolled coil as raw material, the wall thickness can be controlled evenly in the ± 0.2mm or so, and the two ends of the steel pipe according to the United States APl or GB / T9711.1 standard, ERW steel pipe has obvious advantages, such as repairing end groove, the specified length of delivery, etc. In recent years, the natural gas pipeline network engineering and gas companies have widely used ERW steel pipe as the main pipe network pipe.
We've mentioned that roll adjustment had a great influence on ensuring the quality of high frequency welded pipe in the process of production, so now we can talk about techniques of roll adjustment when changing roll.
1) Replace the steel pipe specifications, we generally replace a complete set of roll. Roll adjustment method is: use a wire to pull a centerline from the unit inlet to the outlet, and make the molding line to meet the technical requirements. After changing the roll specifications, we need to make a comprehensive adjustment for forming roller, guide roller, squeeze roller, sizing roller firstly, and then focus on the adjusting the closed hole of forming roll, guide roller, squeeze roller.
2) The role of the guide roller is to control the direction of the pipe seam and tube's bottom line height, ease the edge of the extension, control the rebound of the edge of the tube, ensure that the pipe straight without turning into the squeeze roller. Such as the guide roller adjustment is not good, it is easy to cause steel pipe seam torsion, lap welding, waving deformation around edges and other welding defects in the steel pipe welding process.
3) The squeeze roller is the key equipment of the welded pipe unit, its role is to make the pipe body which the edge of had been heated to the welding temperature to complete the pressure welding under the pressure of extrusion roller. In the production process, wo should control the size of the extrusion roll opening angle. When the extrusion pressure is too small, the weld metal strength will decrease, and it will crack when it is forced; When the extrusion pressure is too large, the welding strength will be reduced and the outer-burr amount will be increased, it will be easy to result in lap welding and other welding defects.
4) In the slow turning starting sequence of the welded pipe unit, we should pay close attention to the bearing rotation of the various parts of the roll, and adjust the roll at any time to ensure that the welding pipe welding quality and process size in line with the requirements.
In the high frequency welding process of production, in order to ensure that the product quality of the high frequency welded pipe meets the requirements of the technical standards and the needs of the customers , we need to analyze the factors that affect the product quality in the steel pipe production process.
Through a month of nonconforming product statistics of Φ76mm high frequency welded steel pipe unit, We believe that the factors that affect the quality of steel pipe products in the production process include raw materials, welding technology, roll adjustment, roll material, equipment failure, production environment and other reasons, etc. Among them, raw materials, welding technology, roll adjustment are key links, 32.44%, 24.85% and 22.72% respectively, the sum of the three links accounted for 80.01%. And the other four elements of the impact on the quality of steel products accounted for 19.99%, are relatively minor links, including roll material, equipment failure, production environment and other reasons. Therefore, in the high frequency welding process of production, the raw materials, welding technology and roll adjustment three links should be controlled carefully.
Effects of raw material on welding quality of carbon steel pipe
Factors affecting the quality of raw materials mainly include three aspects, the unstable mechanical properties of the steel strip, the surface defects of the strip and the large deviation of geometric size. Therefore, tube manufacturers should control from these three aspects.
Effects of high frequency welding on quality of carbon steel pipe
In the process of high frequency welding of steel pipe, welding technology and the control of process parameters, the position of the sensor and resistor,etc., have a great influence on the weld pipe weld quality.
Effects of roll adjustment on quality of carbon steel pipe
From the steel pipe scrap causal analysis diagram, we can get roll adjustment is the operation of the steel pipe.In the production process, when the roll is damaged or abrasive badly ad, we need to replace part of the roll on the unit, or we need to replace the whole roll when the number of a product is enough after continuous production. Tube manufacturers should adjust the roll to obtain a good quality of the pipe.If the roll adjustment is not good, easy to cause the tube seam torsion, welding of steel pipe, lap welding, edge waves, drums and body surface indentation or scratches, big ovality of steel pipe and other defects, so the roll should be grasped roll adjustment skill. So the worker should master the roll adjustment technique when changing the roll.