Difference between welded steel pipe and seamless steel pipe

What is a seamless steel pipe?

Seamless stainless steel pipe - Difference between welded steel pipe and seamless steel pipe

Seamless steel pipe is made of a single piece of metal and has no jointed steel pipe on the surface, which is called seamless steel pipe. According to the production method, the hot rolled tube, the cold rolled tube, the cold drawn tube, the extruded tube, the top tube and the like are seamlessly divided. According to the cross-sectional shape, the seamless steel tube is divided into two types: round and irregular, and the special-shaped tube has a variety of complex shapes such as square, oval, triangular, hexagonal, melon-shaped, star-shaped and finned tubes. The maximum diameter is 650mm and the minimum diameter is 0.3mm. According to different uses, there are thick-walled tubes and thin-walled tubes. Seamless steel tubes are mainly used as petroleum geological drilling tubes, cracking tubes for petrochemical industries, boiler tubes, bearing tubes, and high-precision structural steel tubes for automobiles, tractors, and aviation.
Seamless steel pipe is widely used. General purpose seamless steel tubes are rolled from ordinary carbon structural steels, low alloy structural steels or alloy structural steels with the highest yield, and are mainly used as pipes or structural parts for conveying fluids.

Depending on the use of three different types of supply: a, according to chemical composition and mechanical properties of the supply; b, according to the mechanical performance of the supply; c, according to the water pressure test supply. Pipes supplied by Types a and b, if used to withstand liquid pressure, are also subject to hydrostatic testing.

The special-purpose seamless pipes include seamless pipes for boilers, chemical power, seamless pipes for geological use and seamless pipes for petroleum.
Seamless steel tubes have a hollow cross-section and are used in large quantities as pipes for transporting fluids, such as pipes for transporting oil, natural gas, gas, water, and certain solid materials. Compared with solid steel such as round steel, steel pipes have a lighter weight when subjected to the same flexural and torsional strength and are economical cross-section steels.
Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile drive shaft, bicycle frame and steel scaffold used in construction, etc. The manufacture of ring-shaped parts using steel pipes can improve the material utilization, simplify the manufacturing process, save materials and processing Working hours have been extensively manufactured with steel pipes.

Seamless steel pipe has no longitudinal weld seam. The manufacturing of seamless steel pipe requires a mechanism to force the hole into the billet.
Rotary piercing and rolling is the most common method for producing seamless steel pipe today. The process starts with a conditioned steel round bar, which is heated, pierced, and worked. The bar is made to flow around a piercer point in order to form a hollow billet. The interior of the pipe is supported with a mandrel or a plug while the billet roller is elongated. Sizing of the steel pipe is achieved by additional rolling on the outside diameter.
Seamless steel pipe has 20% higher ASME (American Society of Mechanical Engineers) working pressures compared to welded steel pipe of the same material and size due to having no welded seam. The welded and drawn steel pipe can also have a visible seam that may concern end users.
Another advantage of seamless steel pipe is that it can offer superior corrosion resistance because it has little potential for impurities. Using seamless steel pipe allows you to avoid the potential for defects and differences in malleability that may be associated with the welded area in welded pipes. Unlike welded pipes, seamless pipes do not require testing for weld integrity.
Therefore, seamless steel pipe is often more suitable for critical applications.

What is a welded stee pipe?

astm a790 uns31803 gr2205 welded duplex steel pipe 24 inch sch40s - Difference between welded steel pipe and seamless steel pipe

Welded steel pipe, also called welded pipe, is a steel pipe made by welding a steel plate or strip steel after crimping. The length is generally 6 meters. Welded steel pipe production process is simple, high production efficiency, variety specifications, equipment investment, but the general strength is lower than the seamless steel pipe.

The blanks used for welded steel tubes are steel plates or strips, which are classified into furnaces, electric (resistance welding) tubes and automatic arc tubes because of their different welding processes. Because of its different welding methods, it is divided into two types: straight seam welded pipe and spiral welded pipe. Because of the shape of its end is divided into round welded pipe and shaped (square, flat, etc.) welded pipe.

The welded steel pipe production process begins with the rolling of a steel coil to the desired gauge thickness. The outcome is a coil of a flat strip. The next step involves cutting the strip according to the width that corresponds with the size of the pipe to be produced.
The pipe is formed by moving the cut coil through a series of rollers, and the seam of the pipe is then welded in a chemically neutral environment. A rolling application is used to forge the welded seam, and a heat treating process is used to finish the welded pipe. Welded pipes can then be drawn over mandrels and ground if needed to smooth the welded seam and make it nearly impossible to see with the naked eye.
Because less drawing and annealing are needed in the manufacture of a welded and drawn pipe, the cost of welded and drawn steel pipe can be less expensive than seamless steel pipe and can typically be procured quicker than seamless steel pipe (although stocking of intermediate size starting stock for seamless steel pipe can reduce this lead time as well).

Characteristics of welded steel pipe and seamless steel pipe

Molding process of the steel pipe

1, welded steel pipe is welded, it is cut into by the steel strip narrow steel strip, and then wrapped into a tubular shape with the cold mold. And special welding then a pipe seam welding. Outside welds polished bright. Within the burr of the pipe is not to fight. The only precision welded to fight within the burr.
2, seamless steel pipe is cylindrical ingot hot pull into a tube, so can not see the weld. 

Use classification of steel pipe:

1, water gas pipe is commonly used welded steel pipes, transport fluid and gas called, to feel the pressure, so are relatively thick wall. Older know, rich from poor, a lot of it is called with the characteristics of the times, not too seriously. Original which money galvanized Yeah, two brush paint on the line. Black Well, call it black iron pipe.
2, the conduit is to wear a wire and thin-walled tube. At that time only the standard, no one production. In fact, the eighties and nineties of gas pipes with water.
3, galvanized iron pipe is galvanized welded steel pipe. Galvanized inside and outside, water can be transported. Let Electric used when threading. General are relatively thin wall. Now on the market is poor. Elbow bend angle to blast hole.

Anti-corrosion classfication of steel pipe:

Steel pipe: steel pipe is open at both ends and having a hollow cross-section and their relatively large length, and the vicinity of the steel can be divided, according to the production method of seamless and welded steel pipe, pipe specifications Dimensions (such as diameter or side length) and wall thickness, a very wide range of sizes, from a small diameter capillary tube until the large-diameter up to several meters in diameter. The steel pipe can be used for pipes, thermal equipment, industrial machinery, petroleum exploration, container, chemical industry and for special purposes.

  • Seamless steel pipe: seamless steel pipe is made from a single piece of metal on the surface of steel pipe joints. Production methods can be divided into hot-rolled pipes, cold rolled tubes, cold drawn tubes, extruded tube. Can be divided into two kinds of round and shaped cross-sectional shape. The seamless pipe of the maximum diameter of 650 mm (enlarged diameter tubes), a minimum diameter of 0.3 mm (capillary). According to different thickness can be divided into thick-walled pipes and thin-walled tube. Seamless pipe is mainly used for the petroleum exploration tube, petrochemical cracking tubes, boiler tubes, the bearing tube as well as the automotive, aerospace steel and other high-precision structure.
  • Welded steel pipe: welded steel pipe refers to the bending deformation of the steel strip or steel sheet as round, square and other shapes and then welded into the steel pipe, the surface of the seam. According to the different welding methods can be divided into the arc welded pipe, high or low frequency electric resistance welded pipe, gas pipe, stove pipe, Bundy tube. Weld shape can be divided into Longitudinal and spiral welded pipe. 
  • Welded steel pipe used for oil drilling and machinery manufacturing. The furnace can be used as a water pipe and gas pipe, large diameter welded pipe used for high-pressure oil and gas transmission; spiral welded pipe for oil and gas transmission pipe piles, piers. The welded steel pipe is lower than the cost of seamless steel, high production efficiency.

Difference Between seamless steel pipe and Welded Pipe

Seamless steel pipe and welded pipe are mainly different molding process. Welded steel pipe, such as water pipes, generally through the flat plate by welding after bending up, you can find a seam in the above; is generally thicker in diameter spiral weld. The seamless steel pipe is generally the molten steel through the annular slit of the backlog by stretching out before treatment processes such as molding, so that no seam. In performance, especially on the bearing capacity has greatly improved as compared with ordinary steel, it is often used for high voltage devices. Such as hydraulic equipment, piping connections. The welded steel pipe weld area is its weak link, weld quality is also affecting the overall performance of the main factors

  • Seamless pipe: seamless steel pipe is a kind of hollow cross-section, no seams around the circle, square, rectangular steel. Seamless steel pipe or solid steel ingot is made of the capillary tube through the hole, then through the hot-rolled, cold rolled or cold call is made. Seamless steel pipe with a hollow cross-section, a large number of pipes for conveying fluids, such as steel and solid steel round bar compared to the same torsional strength in bending, lighter, is an economic cross-section steel, widely used in the manufacture structural parts and mechanical parts, such as drill pipe, automotive drive shafts, bicycle frames and construction using steel scaffolding.
  • Welded pipe: welded steel pipe, also known as pipe, plate or strip is formed through the curl made of steel after welding. Welded steel pipe production process is simple, efficient, and more varieties and specifications, equipment, less capital, but the general strength of less than seamless steel pipe.

Concentricity: The process of manufacturing seamless steel 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 steel pipe wall thickness than a slit pipe wall thickness difference. Precision cold-rolled plate (width of 4-5 feet per roll) made a slit pipe. 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. Welded Pipe wall thickness tolerance is very small, and the entire circumference of the wall thickness is very uniform. 

Molding process differences: Seamless steel pipe can be formed one time in the rolling process.
Welded steel pipe is manufacturing with steel strip or steel plate, through bending and different welding processes.

Appearance difference: Seamless steel pipe used steel billet as raw material. The outer surface defects of billet cannot be eliminated by hot rolling process, it is only polished after the product finished. In the process of wall reduction, the defect can only get partially eliminated.
Welded steel pipe made by hot rolled coil as raw material, the surface quality of coil is just the pipe’s surface quality, and easy to control.The surface of hot rolled coil have high quality.
So Welded steel pipe surface quality is much better than seamless steel pipe.

Performance and Usage: Seamless steel pipe has better pressure capacity, strength is higher than ERW welded steel pipe. So it is widely applied in high pressure equipment, and thermal, boiler industries.
Generally the welding seam of the welded steel pipe is the weak point, the quality affect overall performance.
In general, welded steel pipes can withhold 20% less working pressure than seamless ones. This reliability is the prime factor why people go for seamless steel pipe. As a matter of fact, all the industrial pipelines are done with seamless pipes only because the pipes undergo extreme thermal, chemical and mechanical workloads. Welded pipes are more preferred in aerospace, automobile and electronics industries where the budget is comparatively low, and so is the work pressure put on the pipes.
Welding performance: Average Welded Pipe and seamless steel pipe the chemical composition has a certain difference. The production of seamless steel component is only astm the basic requirements. Produce seamless steel pipe 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 steel 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.  For most of seamless steel pipe manufacturers in China, they produce original seamless pipe sizes maximum OD in 20 inch, 508 mm. Where usually is smaller than 16 inch, 406.4 mm, because of the equipment limits. And if client would like to purchase the seamless steel pipe more than above sizes, then hot expanding machining shall be used. But usually this kind hot expanded seamless steel pipe quality could not compare with the original seamless steel pipe.
On the contrary, welded steel pipe don’t have these limitations, sizes available from 1-1/2 inch 48.3mm to 100 inch 2540 mm.
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 Welded 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 pipe 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 pipe joints can be fully exposed to the license pressure. Similarly, Europe and Asia also provides through the eddy current test pipe 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 pipe.
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 Welded 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 Welded Pipe 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 Welded 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.
Cost and prices: Usually the seamless steel pipe cost is higher than welded steel pipes, because the raw material, manufacturing equipment and processes. But sometimes by the market pressure, welded pipe is more expensive, so if you met this situation, don’t hesitate to purchase the seamless steel pipe for the same dimensions.
Wall thickness and diameter: thickness and diameter value of small thin-walled pipe preferably by welding production. Thickness and diameter large thick-walled pipe is best made with the stamping method.

A seamless steel pipe is a pipe that does not have any welding seam. The seamless steel pipe will ideally be a solid metal tube with each end connected to another tube without having any welding joint. These pipes have threads either at one end or at both ends and can be threaded to the end of another hollow tube or pipe.

The presence of any seam on a welded pipe acts as a weak point, however if the tube is seamless, it tends to be solid and overcome various industrial forces and pressures while in operation.

A Seamless steel pipe is extruded and drawn from a billet whereas a welded pipe is produced from a strip that is roll formed and welded to produce a tube.

  • Since a Seamless steel pipe offers a higher range of safety measures it is more expensive than a welded tube.
  • A Seamless steel pipe is relatively short in length, whereas welded tubes can be manufactured in long continuous lengths.
  • A Seamless steel pipe generally doesn’t show any sign of corrosion until and unless it is subjected to a highly corrosive environment, whereas the weld area in the welded tube is much more prone to corrosion attacks.
  • A welded area is considered to be inhomogeneous, thus it exhibits a different malleability and less corrosion resistance as well as greater dimensional variation.
  • A Seamless steel pipe eliminates any such issues and thus offers high corrosion resistance.

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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