Difference between seamless and seam pipe

What is seamless pipe?
Seamless pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell. As the manufacturing process does not include any welding, seamless pipes are perceived to be stronger and more reliable.

What is seam pipe?
Seam pipe, also known as welded pipe. Welded pipe is formed by rolling plate and welding the seam (usually by Electric resistance welding (“ERW”), or Electric Fusion Welding (“EFW”)). The weld flash can be removed from both inner and outer surfaces using a scarfing blade. The weld zone can also be heat-treated to make the seam less visible. Welded pipe often have tighter dimensional tolerances than the seamless type, and can be cheaper to manufacture.

Large-diameter pipe (25 centimetres (10 in) or greater) may be ERW, EFW or Submerged Arc Welded (“SAW”) pipe. There are two technologies that can be used to manufacture steel pipes of sizes larger than the steel pipes that can be produced by seamless and ERW processes. The two types of pipes produced through these technologies are longitudinal-submerged arc-welded (LSAW) and spiral-submerged arc-welded (SSAW) pipes. LSAW are made by bending and welding wide steel plates and most commonly used in oil and gas industry applications. Due to their high cost, LSAW pipes are seldom used in lower value non-energy applications such as water pipelines. SSAW pipes are produced by spiral (helicoidal) welding of steel coil and have a cost advantage over LSAW pipes, as the process uses coils rather than steel plates. As such, in applications where spiral-weld is acceptable, SSAW pipes may be preferred over LSAW pipes. Both LSAW pipes and SSAW pipes compete against ERW pipes and seamless pipes in the diameter ranges of 16”-24”.

Historically, seamless pipe was regarded as withstanding pressure better than other types, and was often more available than welded pipe.

Concentricity: The process of manufacturing seamless pipe is a hole punched out in a stainless steel billet temperature of 2200 ° f the, in this high temperature, the tool steel by stamping and drawing softens and spirally from Kongzhong Cheng-shaped out. So that the wall thickness of the pipe is not uniform and high eccentricity. Thus astm allows seamless pipe wall thickness than a slit tube wall thickness difference. Precision cold-rolled plate (width of 4-5 feet per roll) made a slit tube. These cold rolled sheet is usually the largest wall thickness difference is 0.002 inches. The steel sheet was cut into a width πd, where d is the outer diameter of the pipe. seam pipe wall thickness tolerance is very small, and the entire circumference of the wall thickness is very uniform. 

Welding performance: Average seam pipe and seamless pipe the chemical composition has a certain difference. The production of seamless steel component is only astm the basic requirements. Produce seamless tube steel with the chemical composition suitable for welding. For example, silicon, sulfur, manganese, oxygen and triangle ferrite and other elements can be mixed according to a certain proportion in the welding process with an easy transfer heat weld, so that the entire weld penetration. The lack of the above chemical composition of the steel, seamless, for example, in the welding process will produce a variety of factors of instability, is not easy to weld and welding impervious. 

Grain size: usually, the grain size of the metal and the heat treatment temperature and to maintain the same temperature for the time. Therefore, annealed seam and seamless pipes are the same grain size. If the slit pipe with minimum cold treatment, grain size smaller than the grain size of the weld metal of the weld, and otherwise, the grain size is the same. 

Strength: the strength of the pipe depends on the alloy composition, which contains the same alloy and the same heat treatment of seamless and seamed pipe strength are the same in essence. After tensile test and three-dimensional vibration test, tear seam pipe occurs almost exclusively in a place away from the welding point or heated areas. This is because the weld impurities less and the nitrogen content is higher, and thus the strength of the weld is better in other parts. ASME Boiler and Pressure Vessel Association, however, that a slit tube can only afford 85% of the license pressure, which is mainly due to the collection of data as early as welding equipment in use today have improved. ASME requirements 100% by ultrasonic test tube joints can be fully exposed to the license pressure. Similarly, Europe and Asia also provides through the eddy current test tube joints to guarantee the performance of the welding quality, eddy current testing require the approval of the legal procedures and permit institutions. The trent eddy current testing by the permission of the Swedish Ministry of Energy. The ASME think current loss is smaller quality performance is based on a slit tube. 

Corrosion resistance: corrosion resistance, good or bad is also vary depending on the composition of the alloy. The same chemical composition fully heat-treated seamless and the seam pipe corrosion resistance. ASTM provide supplementary test can prove the corrosion resistance of the weld is equal to or better than the metal being welded. Incomplete seam tube welding heat treatment in acidic chloride environment, corrosion will be accelerated, but only need corrosion test is, in fact, their environment is not so bad. Bending and extension: extension of the welding at the following tests can be specified by ASTM Verification: bend 45 °, then bent to 90 °, then flattened along the weld seam pipe Repeat the above steps; then turned so that the weld bending diameter up to 180 °. Weld quality standards adopted by the tear or intergranular separation are not allowed in the case of 40 times magnification. Pipe bending radius is controlled by the composition of the alloy, the general minimum bend radius for 2d. Conditions of the welding seam in a neutral or a state of compression. Moreover, the piping should be annealed to reduce its hardness, thereby improving the bending performance. 

Price: Price seam pipe is usually only half of the seamless. 

Wall thickness and diameter: thickness and diameter value of small thin-walled tube preferably by welding production. Thickness and diameter large thick-walled tube is best made with the stamping method.

Source: China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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  • https://en.wikipedia.org/wiki/Pipe_(fluid_conveyance)

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