Seamless pipe vs Welded pipe

Difference seamless pipe and welded pipe
Concentricity: seamless pipe manufacturing process is at a temperature of 2200 ° F in a stainless steel billet punching out a hole in this high temperature tool steel by stamping and drawing becomes soft and spirally from the Kong Zhongcheng shaped out. Such uneven wall thickness of the pipe and the eccentric high. Thus ASTM standard allow the wall thickness difference of seamless pipes is bigger than the welded pipes’. Slotted tube is made by precision cold-rolled plates (4-5 feet) per roll width. These cold rolled sheet is usually the maximum wall thickness of 0.002 inches. The steel sheet was cut to the width πd where d is the outer diameter of the pipe. Slit pipe wall thickness tolerances are small, and the entire circumference of the wall thickness is very uniform.

Welding performance: general tube and seamless pipe has certain differences on the chemical composition. The production of seamless pipe steel composition is only the basic requirements to meet ASTM. While the production of the chemical composition of the steel slotted tube containing suitable for welding. For example, silicon, sulfur, manganese, oxygen and the triangle of ferrite and other elements at a certain proportion of mixed can be generated during the soldering process the solder melting and an easy transfer of heat, so that the entire weld penetration. Lack of the above chemical composition of the steel pipe, such as seamless tubes, in the welding process will produce a variety of factors of instability, is not easy to weld and welding impervious.

Grain size: Typically, Metal grain size and heat treatment temperature and keep the same temperature is related with the time. Therefore, the annealed the same seam pipe and seamless pipe grain size. If there is a seam tube with a minimum of cold treatment, the grain size of the weld seam is less than the grain size of the weld metal, otherwise, the grain size is the same.

Strength: the strength of the pipeline depends on the alloy composition, and thus contain the same alloy and the same heat treatment of seamless pipe and slotted tube essentially are consistent strength. After tensile testing and three-dimensional vibration test, slotted tube tear occur almost exclusively in a place away from the welding point or heated area. This is because fewer impurities and a slightly higher nitrogen content of the weld, and thus the strength of the weld at better than the other region. However, the ASME Boiler and Pressure Vessel Association seam pipe can only bear 85% of the allowable pressure, which is mainly due to the data collected as early as today has improved welding equipment. ASME regulations 100% seam tube can withstand the allowable pressure by ultrasonic testing. Similarly, Europe and Asia also provides seam pipe to ensure the quality of its welding performance by means of eddy current testing, eddy current testing require the approval of the legal procedures and licenses held by institutions. Trent eddy current testing by the permission of the Swedish Ministry of Power. ASME small current loss is based on the quality performance of the slotted tube.

Corrosion resistance: good or bad corrosion resistance also depends on the composition of the alloy. Full heat treatment of a seamless pipe with the same chemical composition and by the corrosion resistance of the slit pipe is consistent. The ASTM provides supplementary tests proved weld corrosion resistance equal to or better than the metal being welded. In acidic chloride environment, not fully heat at the welding of the slit pipe corrosion will be accelerated, but only the needs of the corrosion test, in fact, the environment is not so bad. Bending and extension: the extension of the welding prescribed by ASTM following tests to verify: bent 45 ° bent to 90 °, flattened along the weld; then turned the seam pipe Repeat the above steps to make the weld The curved inner diameter is 180 °. Weld quality by the standards is not allowed to appear in the case of 40-fold magnification tear or intergranular separation. Pipe bending radius is controlled by the composition of the alloy, the general minimum bend radius of 2D. The ideal welding condition is a seam in a neutral or compressed state. Moreover, the pipes should be an annealing treatment in order to reduce its hardness, thereby improving the bending performance.


Post time: Nov-11-2019