Difference between seam and seamless tube
Concentricity: The seamless manufacturing process punches the stainless steel billet at 2200 F. At this temperature, the tool steel becomes soft and stamped, pulling the spiral shape loyally from the hole. The thickness of the tube wall is not uniform and the eccentricity is high. Therefore, the thickness difference of seamless pipe wall allowed by ASTM is quite different from that of pipe joint. The joint is made of precision cold rolled sheet (4-5 feet wide per coil). Cold rolled sheets are usually the largest difference of 0.002 inches in wall thickness. The steel plate is cut to a width of PI d, where D is the outer diameter of the tube. The wall thickness tolerance of slit pipe is small, and the whole wall thickness is very uniform.


Welding performance: There are some differences in the general chemical composition between seamless pipe and pipe joint. The production of seamless steel components simply meets the basic requirements of astm. Its steel pipe joints contain chemicals suitable for welding. For example, triangular ferrites of silicon, sulphur, manganese, oxygen and other elements are mixed in a certain proportion to produce easily transferable hot-welded materials during the welding process, thus making the whole weld penetrate. For example, the lack of chemical composition of seamless pipes beyond steel pipes can lead to various uncertainties in the welding process, making it difficult to weld and impermeable to weld.


Grain size: Usually, the grain size of metals is related to the same temperature as the heat treatment temperature and time. Therefore, the seamless grain sizes of annealed and cut tubes are the same. If the minimum cold treatment is applied to the pipe joint, the grain size of the weld metal is smaller than that of the weld metal, otherwise, the grain size is the same.


Strength: The strength of the pipe depends on the alloy composition, which contains the same alloy and heat treatment of the same seamless and jointed pipe basically uniform strength. After tension test and three-dimensional vibration test, the tearing of pipe joints occurs almost exclusively away from the welding point or heating place. This is because there are fewer impurities and higher nitrogen content in the weld, so the strength of the weld is better than that of other regions.  However, ASME Boiler and Pressure Vessel Association believes that pipe joints can only withstand 85% of the allowable pressure, mainly due to data collected on improved welding equipment used as early as today. ASME stipulates that pipeline joints are fully allowed to withstand pressure by 100% ultrasonic testing. Similarly, Europe and Asia also provide eddy current testing through pipe cutting, which ensures quality, requires eddy current testing through legal procedures, and allows their institutions to weld. Trent's Swedish license for eddy current testing in the power sector. ASME believes that the current loss is based on the high performance of smaller pipe joints.


Corrosion resistance: Corrosion resistance depends on the composition of the alloy. The same chemical composition and heat treatment of seamless steel pipe have completely cut the pipeline corrosion resistance is the same. Supplementary Test ASTM provides weld corrosion resistance equivalent to or better than that of welded metals. In acid chloride environment, incomplete heat treatment accelerates corrosion of welded pipes, but only corrosion tests are needed. In fact, the environment is not so bad. Bending and Tensile Properties: Welding extension can be verified by ASTM after testing: bending 45 degrees, then bending to 90 degrees, then flattening along the weld; and then turning the pipe joint to repeat the above steps, so that the inner diameter of the weld bending reaches 180 degrees. Welding quality standards are adopted between cases where tearing or separation of grains is allowed, and the magnification is 40 times. The bending radius of the pipe is controlled by the composition of the alloy, and the minimum bending radius is generally 2 days. Welding conditions are ideal for neutral or compression. In addition, the tube should be annealed to reduce its hardness and thus improve its bending properties.