Brief Introduction of Welded Steel Pipe

Welded steel pipe, also known as welded pipe, is a steel pipe which welded by steel plate or strip after the coil shaping. Welding steel pipe is simple in production process, high in production efficiency, various in specifications, and the equipment capital is not much. Generally, the strength of welded steel pipe is lower than the seamless steel pipe. Since the 1930s, with the rapid development of rolling production of high quality cold rolling strip steel and progress of welding and inspection technology, welding quality continuously improve. What’s more, specifications of welding steel pipe are increasing and instead of the seamless steel pipe in more and more fields. According to the form of Welded steel pipe weld, it is divided into longitudinal and spiral welded pipe.

erw process Sizing Mill - Brief Introduction of Welded Steel Pipe

The billet that welded steel pipe adopted is steel plate or strip steel. Because of the different welding process, welded steel pipe is divided into furnace welded pipe, welded (erw) pipe and automatic arc welding pipe. Due to its different welding form, it can be divided into straight seam welded pipe and spiral welded pipe. Because its shape of end is different, it can be divided into circular welded pipe and alien (square, flat, etc) welded pipe. Due to its different material and use, it can be divided into the following varieties:

  • GB/T3091-1993 ( galvanized welded steel pipe for low pressure fluid conveying). It is mainly used for conveying water, gas and heating hot water or steam, air, oil and other general low pressure fluid and pipe for other purpose. It is represented by material level Q235A steel.
  • GB/T3092-1993 ( galvanized welded steel pipe for low pressure fluid conveying). It is mainly used for conveying water, gas and heating hot water or steam, air, oil and other general low pressure fluid and pipe for other purposes. It is represented by material level Q235A steel.
  • GB/T14291-1992 (welded steel pipe for mine fluid conveying). Straight seam welded steel pipe is mainly used for mine forced draught, drainage, wind shaft gas. It is represented by material level Q235A, B grade steel.
  • GB/T14980-1994 (large diameter welded steel pipe for low pressure fluid conveying). It is mainly used for conveying water, sewage, gas, low pressure fluid such as air, steam heating and other uses. It is represented by material level Q235A steel.
  • GB/T12770-1991 (stainless steel welded pipe for mechanical structure). It is mainly used in machinery, automobile, bicycle, furniture, hotel and restaurant decoration and other mechanical parts and components. Its representative materials are 0 cr13, 1 cr17, 00 cr18ni9 cr19ni11, 1, 0 cr18ni11nb, etc.
  • GB/T12771-1991 (stainless steel welded pipe for fluid conveying). It is mainly used for low pressure corrosive medium. Its representative materials are 0 cr19ni9 cr13, 0, 00 cr19ni11, 00 cr18ni11nb cr17, 0, 0017 cr17ni14mo2, etc.

erw pipe 1 - Brief Introduction of Welded Steel Pipe

Types of Welded Steel Pipe
1. Welded steel pipe (GB/T3092-1993) used in Low-pressure fluid delivery, also known as the general welded pipe, commonly known as black tube. It is the welded steel pipe that used to transport of water, gas, air, oil and heating steam, and other generally fluids with lower pressure. Steel pipe is divided into ordinary steel pipe and thickened pipe according wall thickness; is divided into non-threaded steel pipe (light pipe) and threaded steel pipe according to the form of pipe end. The specifications of the steel pipe are denoted by nominal caliber (mm), and the nominal caliber is the approximate value of the inner diameter. It traditionally uses inches to express, such as 11/2 and so on. Welded steel pipe used in Low-pressure fluid delivery in addition to directly use for the transport of fluid, but also is used as the original tube of galvanized welded steel pipe used in Low-pressure fluid delivery.
2. Galvanized welded steel pipe (GB/T3091-1993) used in Low-pressure fluid transmission, also known as galvanized welded steel pipe, commonly known as white tube. It is the hot dipping galvanized welded (butt weld or electrowelding) steel pipe used to transport water, gas, air oil and heating steam, warm water and other generally fluids in lower pressure. Steel pipe is divided into ordinary galvanized steel pipe and thick galvanized steel pipe according to wall thickness; is divided into non-threaded galvanized steel pipe and threaded galvanized steel pipe according to the form of pipe end. It traditionally uses inches to express, such as 11/2 and so on.
3. Ordinary carbon steel electric wire conduit (GB3640-88) is used in electrical installation ( such as the industrial and civil construction and installation of electrical equipment and other works) to protect the wire of the steel pipe.
4. LSAW steel pipe (YB242-63) is the pipe that the weld longitudinally parallel to steel pipe. It is usually divided into metric welded steel pipe, welded thin-walled pipe, transformer cooling tubing and so on.
5. SSAW steel pipe (SY5036-83) for pressurized fluid delivery is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature and welded by double-sided submerged arc welding, used for pressurized fluid delivery. The loading capacity of steel pipe is strong, welding performance is good, after a variety of strict scientific inspection and testing, it can be used safely and reliably. The diameter of steel pipe is big, transport efficiency is high, and it can save the laying of pipeline investment. So it is mainly used for conveying oil and gas pipelines.
6. ERW steel pipe used for pressurized fluid transmission (SY5038-83) is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, welded by high-frequency lap welding, used for pressurized fluid transportation. The loading capacity of steel pipe is strong, plasticity is good, and it is easy to weld and machine shaping. After a variety of rigorous and scientific inspection and testing, the pipe is safe and reliable to use, the diameter of steel pipe is large, transport efficiency is high, and it can save the laying of pipeline investment.
7. Spiral welded steel pipe (SY5037-83) used in general low-pressure fluid transmission is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, use double-sided automatic submerged arc welding or single-sided welding method to weld. It is used for water, gas, air and steam and other general low-pressure fluid transmission.
8. ERW steel pipe (SY5039-83) used in general low-pressure fluid transmission is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, use high-frequency lap welding to weld,. It is used for general low-pressure fluid delivery.
9. Spiral welded steel pipe (SY5040-83) used as pile is made of hot-rolled steel coil as tube blanks, spirally forming in normal temperature, use double-sided submerged arc welding or high-frequency welding to make. It is used for civil construction, wharf, bridge and other foundation pile steel pipe.

Classification of welded steel pipe

  • 1, High frequency welded steel pipe features: tubular good, uniform thickness, internal and external burrs produced by the welding tool calibrating the appropriate online through strict control of non-destructive testing of weld quality, high degree of automation, low production costs. But relatively thin wall thickness, diameter is relatively small, usually no more than a wall thickness of 12mm, diameter generally does not exceed 610mm, particularly suitable for the production of steel tube truss structure.
  • 2, LSAW pipe features: welding under static conditions, high weld quality, short welds, the probability is very small defects. By expanding full-length steel tubular good, precise size, wide range of pipe wall thickness and diameter range, the diameter range up 406-1829mm, wall thickness range up 6.0-60mm, high degree of automation, Compared to seamless steel, it is lower production costs, for buildings, bridges, dams, offshore platforms and other steel bearing with columns, large span structures as well as wind and seismic requirements for electrical tower mast structure.
  • 3, Spiral submerged arc welded pipe features: spiral weld line distribution, long welds, especially under dynamic conditions is in the welding, the weld had a chance to cool and left the molding point, easy to produce welding hot cracking. Direction parallel to the weld crack, a certain angle the axis of the steel pipe, typically between  30-70 °. This angle is just consistent with shear failure angle, so the bending, tensile, compressive and torsional performance is far better than LSAW pipe welding position and because restrictions, saddle ridge seam and fish the impact beautiful. In addition, the construction process, intersecting line pipe weld spiral welded parent node of fragmented spiral seam, a greater welding stress, thus greatly weaken safety performance components, and therefore efforts should be strengthened spiral welded non-destructive testing of welds, ensure the welding quality, otherwise important occasion not to use steel spiral submerged arc welded pipe.

Technical Requirement for Welded Steel Pipe

According to the API/ASTM stadnards, there are many technical requirements for producing welded steel pipe.
The nominal pipe diammeter ranges from 6-150mm, nominal wall thickness ranges from 2.0-6.0mm and the length of the pipe is usually from 4 to 10. The pipe surface shoule be smooth, no collapse, no cracks, no delamination, and no lap welding defects exist. The wall thickness is not allowed to over the deviation, no scratches, no weld dislocation, no burns and scarring and other minor defects.
Welded steel pipe should perform mechanical test, flattening test and flaring test to achieve the standard requirements. 2.5 Mpa internal pressure test is allowed to keep over 1 minue without leakage. It allows use eddy current testing method instead of the hydrostatic test. After the eddy current testing, welded steel pipe will be cut to a predetermined length by flying saw and then flip-off from the assembly line. Then both ends of the pipe should be flat head chamfering, painting, marking and hexagonal packing before delivery.

The Welding Quality of Welded Steel Pipe

Welding quality of welded steel pipe refers to the degree to which the welding product meets the design technical requirements. Welding quality not only affects the use performance and life of welding products, more importantly, affects personal and property safety. Welding quality is usually ensured by design quality, processing quality, quality inspection and post-weld treatment and other links of the product.

Design Quality

The type of joint used in the welding product and its calculated strength should meet the actual carrying capacity. Welding method should be suitable for the characteristics of components, and its economical efficiency should be good. The welding process should be able to minimize stress, deformation and stress concentration. Production labor and material consumption should be as small as possible, the convenience of flaw detection should also be taken into consideration when design the joint.

Processing Quality

The performance of adopted the base metal, wire, flux or welding electrodes and other welding materials should meet the design requirements. The performance of welder, auxiliary equipment and testing equipment should be good. Before welding, the welding material should be dried according to the provisions, the welding groove of workpiece should meet the requirements and remove the cutting residue, cracks and dirt.

Quality Inspection

Quality inspection runs through the whole production process from design to finished product, we must ensure that the test method used in the quality inspection process is rationality, the reliability of the testing instrument and inspection staff technical level. The properties of the joints, physical properties, mechanical properties, microstructure, chemical composition, corrosion resistance, appearance dimensions and welding defects of products after welding should be checked by means of various inspection methods.
Welding defects can be divided into external defects and internal defects. External defects include: excess height does not meet the requirements, welding tumor, undercut, crater, arc burns, surface pores, surface cracks, welding deformation and warping. Internal defects include: cracks, not penetration, not fused, slag and porosity. The most harmful in welding defects is the crack, the followed is lack of penetration, incomplete fusion and slag inclusion, pores and structure defect. Individual flaws are allowed to exist. The number and the nature of allowed defects are determined by the using conditions and the quality assessment criteria of the product. If the surplus height of welding line is too high, it is allowed for those products by the static load, but it is not allowed for those products by cyclic fatigue loading in high frequency, even the normal excess weld metal also has to be cut off. The presence of welding defects is related to the groove processing and assembly accuracy, the rigor degree of the welding process, the technology of the welder and other factors.

Surface Treatment of High-frequency Welded Steel Pipe

long-distance oil/gas pipeline is an important way of energy security, in the oil (gas) pipeline anti-corrosion construction process, the surface treatment of high-frequency welded steel pipe is one of the key factors to determine the useful life of the pipeline. It is the premise that the erosion resistant coating can be firmly bonded to the steel pipe. According to the research institutions, the life of the erosion resistant coating depends on the coating type, coating quality, construction environment and other factors. The surface treatment of steel pipe accounted for about 50% on the life of the erosion resistant coating. therefore, we should be strictly in accordance with the requirements specification of erosion resistant coating to steel pipe surface, continue to explore and summarize, and constantly improve the surface treatment of steel.
1. Cleaning
Using solvents and emulsions to clean the surface of steel to achieve the removal of oil, grease, dust, lubricants and similar things, but it can not remove the rust, oxide, welding, etc. on steel surface, so it only can be an auxiliary means in anti-corrosion production.
2. Toolrust-removal
We mainly use steel wire brush and other tools to polish the steel surface, which can remove loose or tilt oxide, rust, welding slag and so on. Manual tool derusting can reach Sa2 level, power tools derusting can reach Sa3 level. If the steel surface attached to a solid iron oxide skin, the effect of toolrust-removal is not ideal, and can not up to the depth of the anchor required by anti-corrosion construction.
3. Pickling
Generally, we use chemical and electrolytic two methods for pickling treatment. Pipeline corrosion only uses chemical pickling, which can remove the oxide, rust and the old coating. And sometimes it can be used as a re-treatment after derusting by sandblast. Although using chemical to clean the surface can achieve a certain degree of cleanliness and roughness, but the anchor is shallow, and it easy to cause pollution to the environment.
4. Abrasive blasting
Abrasive blasting is through high-power motor rotating to drive jet vane to rotate on high speed to make steel sand, steel balls, wire segments, minerals and other abrasives doing spray treatment on the surface of the steel pipe in the centrifugal force. This method not only can completely remove the rust, oxides and dirt, but the steel pipe under the action of the abrasive impact and friction also can achieve the required uniform roughness.
After the spray treatment, we not only can expand the physical adsorption of the surface of the tube, but also enhance the coating and the pipe surface of the mechanical adhesion. Therefore, the spray (throw) treatment is the ideal way to rust rust pipe repair. In general, shot peening (sand) derusting is mainly used for pipe internal surface treatment, shot blasting (sand) derusting is mainly used for pipe external surface treatment.

Welding Inspection of Welded Steel Pipe

The contents of the welded steel pipe welding inspection include the inspection of the materials, tools, equipment used in the whole production process, process and finished product from drawing design to product completed. It is divided into three stages: pre-weld inspection, inspection in welding process, finished product inspection after welding. According to whether damage the welded carbon steel pipe or not, test methods can be divided into destructive testing and non-destructive testing two categories.

Pre-weld inspection

Pre-weld inspection includes the inspection of raw materials (such as base metal, electrodes, flux, etc.) and the inspection of welding structure design.

Inspection in welding process

Inspection in welding process includes the inspection of welding process specifications, the inspection of weld size, the inspection of fixture conditions and structural assembly quality.

Finished product inspection after welding

There are many methods of finished product inspection after welding, commonly used are the following:
No 1. Appearance inspection
The appearance inspection of the welded joint is a inspection method with simple procedure, but it is widely used, and it is an important part of the finished product inspection. It is mainly used to find the defect on the surface of welded steel pipe weld seam and the size of the deviation. We generally observe through the naked eye, or testing by virtue of the standard model, gauge and magnifying glass and other tools. If there is a defect on the surface of the weld seam, it is possible that there is a defect in the weld.
No 2. Confidentiality testing
The defects of brazing joints of welded seam of welded vessel for the temporarystorage of a gas orliquid, such as perfoliate cracks, porosity, slag inclusion, incomplete fusion and loose organization, etc. can be found by compactness test. Compactness test includes kerosene test, water-bearing test, hose test, etc.
No 3. Strength test of the pressure vessel
Except carrying out encapsulation test, we also should carry out strength test to pressure vessel. Two kinds of methods are commonly, hydraulic pressure test and air pressure test. Each of them can test the welded seam compactness of vessel and pipe working under pressure. Pneumatic tests are more sensitive and rapid than hydrostatic tests, the tested products need not to drain off water,it is particularly suitable for difficult drainage products. But the risk of testing is bigger than the hydraulic test. During the test, the corresponding safety and technical measures must be observed to prevent accidents during the test.
No 4. Physical inspection method
Physical inspection method is a method that using some physical phenomena to measure or test. the inspection of materials or parts of the internal defects, generally use non-destructive testing methods. Currently, non-destructive testing includes ultrasonic testing, ray detection, penetration testing, magnetic detection and so on.
① Ray detection
Ray detection is a detection method that use the characteristics of ray can penetrate the material and has attenuation in the material to find defects. Ray inspection is mainly used to test the cracks inside the weld, incomplete penetration, porosity, slag and other defects.
② Ultrasonic testing
Ultrasound can spread in the metal and other uniform media, due to it will produce reflection in the interface of different media, it can be used for testing internal defects. Ultrasonic can test the defect of any welding material and on any part, and it can be more sensitive to find the location of defects. But the nature of defects, shape and size is more difficult to determine. So ultrasonic testing often used in conjunction with the ray test.
③ Magnaflux inspection
Magnaflux inspection is a detection method that use the leakage of magnetic produced by magnetic field, magnetized iron, magnetic metal parts to find defects. According to different methods of magnetic flux leakage, it can be divided into magnetic powder, magnetic induction and magnetic recording method, magnetic powder is the most widely use method. Magnetic flaw detection can only discover the defect on the surface or the near surface of the magnetic metal.
④ Penetration testing
Permeability testing uses certain liquids such as the permeability of the physical properties to find and display defects, including color inspection and fluorescence detection It can be used to check the defect on the surface of ferromagnetic and non-ferromagnetic material.

The Groove of The Welded Steel Pipe

In the production of welded steel pipe, the groove of the tube is the shape of the cross-section, the general manufacturers in the slitting directly into the high-frequency welding, the groove is a “I” shape. When the thickness of the welding material is greater than 8 ~ 10mm above the pipe, if the use of this “I” shaped groove, because the relationship between the curved arc, you need to melt off the tube first contact with the inner layer, forming a high Burr, and easy to cause the center of the plate and the outer layer of insufficient heating, affecting the welding strength of high-frequency weld. Therefore, in the production of thick-walled tube, the tube is best through the planing or milling edge treatment, so that the groove was “X” shape, the practice proved that this groove for the uniform heating to ensure the quality of the weld seam of welded steel pipe has a great relationship. The selection of the groove shape also affects the size of the adjustment angle. The design of the welded joint is a weak link in the design of the welding project of welded steel pipe. It is not uncommon for the construction of many steel structures. The design of the groove is not from the hand of the welding engineering technician, the hard sleeve standard and the poor performance. The groove form plays an important role in controlling the internal quality of the weld and the quality of the welded structure. The groove design must test the fusion ratio of the base metal, the welding space, the welding position and the comprehensive economic benefits. The lateral shrinkage value ΔB should be calculated by the following equation.
ΔB = 5.1Aω / t + 1.27d
Where Aω – weld cross-sectional area, mm, 
           t – plate thickness, mm, 
           d – weld root gap, mm.
After finding the relationship between ΔB and Aω, we can analyze and process the data according to the relationship list, optimize the design, and finally determine the form of butt weld.

High Frequency Welded Steel Pipe Quality Inspection: Optical Microscope

In the production process of welded steel pipe, quality inspection is a very importance of foundation link. In general, pipe manufacturer (yaang) will use optical microscope to test weld seam. Optical microscope is light waves to deal with visible and near-visible, bunching the beam to irradiate on the object, the imaging falls on the human retina, photosensitive film or other recording system, breaking the limitations of human physiology, the visual extension to The human eye can not tell the microscopic world. It is the most important optical precision instrument used to observe, record and study the fine structure of the object being examined.
High-frequency welded steel pipe is using the welding method to effectively connect the metal material. When pipe manufacturers produce high-frequency welded steel pipe (such as ERW steel pipe, LSAW steel pipe, spiral welded pipe), many factors in the welding process directly affect the weld metal and heat affected area of the macrostructure and microstructure, welding defects and welding joints performance. Therefore, the study of the weld area of the organization, welding defects and joint performance, as soon as possible to find and solve the welding quality problems, must use the macro test analysis and microstructure test.
Macro-inspection, including the appearance of quality inspection and low-power tissue analysis, you can understand the welding structure and welding products, the main appearance, resulting in defects of the nature of the site and its overall relationship with the welding structure and so on. It is necessary to assess and control the quality of the pipe and to prevent major accidents. This requires a microscopic examination of a stereomicroscope.
Microstructural inspection is the process of analyzing and testing the microstructure of weld metal, the characteristics of fusion structure, and the characteristics of weld heat affected zone. To understand the state of microstructure, to ensure the quality of welded pipe, you need high-power microscope observation, recording microstructure characteristics.

How to Control Weld Gap of Welded Steel Pipe

When the factories of yaang manufacture welded steel pipe, the strip is fed into the welded pipe unit, rolled by the multi-way roll, the strip is gradually rolled up to form the circular tube with the opening gap, the pressing amount of the pressing roller is adjusted so that the gap of the weld is controlled at 1 ~ And make the ends of the weld flush. If the gap is too large, resulting in reduced proximity effect, insufficient eddy current heat, weld intergranular junction failure caused by non-fusion or cracking. If the gap is too small is caused by the adjacent effect increases, welding heat is too large, resulting in weld burns; or weld seam formed a deep pit after squeezing and rolling, which affects the surface quality of the weld.
1.The control of welding temperature
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the correlation formula, the high-frequency eddy current heat is mainly affected by the current frequency, the eddy current thermal power is proportional to the square of the current excitation frequency, and the excitation frequency is excited by the excitation voltage, Current and capacitance, inductance effects.
The excitation frequency formula is:
F = 1 / [2π (CL) 1/2]
Where the f-excitation frequency (Hz); the capacitance (F) in the C-excitation circuit, the capacitance = the charge / voltage; the inductance, inductance = magnetic flux / current in the L-excitation circuit
In the above equation, the excitation frequency is inversely proportional to the capacitance in the excitation circuit, the square root of the inductance, or is proportional to the square root of the voltage and current. As long as the capacitance, inductance or voltage in the loop is changed, the current can change the magnitude of the excitation frequency Control the purpose of welding temperature. For low carbon steel, welding temperature control at 1250 ~ 1460 ℃, to meet the wall thickness of 3 ~ 5mm penetration requirements. In addition, the welding temperature can also be achieved by adjusting the welding speed.
When the input heat is insufficient, the edge of the heated weld does not reach the welding temperature, the metal structure remains solid, forming unmelted or not penetrated; when the input heat is insufficient, the edge of the heated weld exceeds the welding temperature, Burn or drop, so that the weld to form a melting hole.
2.The control of extrusion pressure
After the two edges of the tube are heated to the welding temperature, the common metal grains penetrate and crystallize under the extrusion of the squeeze roll to form a firm weld. If the extrusion pressure is too small, the number of common crystals is small, the weld metal strength decreases, the force will produce cracking; if the extrusion force is too large, will make the molten state of the metal is squeezed out of the weld, The weld strength, and will produce a lot of internal and external burrs, and even lead to welding joints and other defects.
3.The control of high-frequency induction coil position
The high frequency induction loop should be as close as possible to the squeeze roller position. If the induction circle is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, the weld strength decreases; on the contrary, the edge of the weld is insufficiently heated, and the molding is bad after extrusion.
4. The control of resistance
The resistance is a or a group of pipe dedicated magnetic bar, the cross-sectional area of the resistor should not be less than 70% of the cross-sectional area of the pipe diameter, the role is to make the induction coil, pipe edge and the edge of the magnet to form an electromagnetic induction Loop, resulting in proximity effects, eddy current heat concentrated in the vicinity of the edge of the pipe weld, so that the edge of the tube heated to the welding temperature. The resistor is dragged in a tube with a wire and its center position should be relatively fixed at the center of the squeeze roller. When the boot, due to the rapid movement of the tube, the resistance of the inner wall of the tube by the friction and wear and tear, need to be replaced frequently.
5.Clear the scar
The weld by welding and extrusion will produce scar, need to clear. The cleaning method is to fix the tool in the rack, the rapid movement of the welding pipe, scraping scrap scar. The burrs inside the pipe are generally not cleared.

The Difference Between the Black Steel Pipe and the Welded Steel Pipe

At present, nearly each family is equipped with different types of the pipes to deliver water, gas as well as the warm steam. They are the parts of your family, and it is necessary to repair them occasionally. Thus, how to choose the pipes you really need is important. Knowing the main differences between these two pipes will help you find out the pipes suitable for your home. The main difference between the two pipes is their basic properties. Most of the black steel pipes are iron pipes, which have high carbon as well as the ferrite.  And its name black steel pipe comes from the outer black oxide cover on the surface. Ever if the black steel pipe is a type of the structural steel pipe, they are not the same completely.
The second difference between steel pipe and black iron pipe is their applications. For example, the welded steel pipe is often used to like your water supply system to the general water supply system, while the black steel pipe is most commonly utilized to deliver gas and oil in your house. In earliest time, people used black steel pipes to deliver water. However, there is no corrosion resistant layer to keep the black steel pipe from being rusted, so people chose to use welded steel pipe that has longer service time to deliver water.
As for the usage, the black steel pipe is beneficial to installing all kinds of the fittings because of lacing corrosion resistant layer. Thus, it has more chance to connect with other pipes to meet different building construction demands. While there are many kinds of welded steel pipes and most of them are covered with a anticorrosion layer, so they have longer using time but are not easily to link to other pipes. In terms of maintenance, the welded steel pipes have a better durability than that of the black steel pipes. In addition, because most of the welded steel pipe has welded seams, so it is not easy to occur leakage in the middle of delivering. And some of the black steel pipes have seams, so the welded steel pipe is much safer than the black steel pipes.
And as the black steel pipes are fragile, it is easy to damage the mild steel pipe in the course of production. However, the protection coverage of the welded steel pipe will flake off over time, causing blocking the pipelines. Thus, when choosing these two pipes, you need to consider carefully. Finally, the price of welded steel pipe as well as the black steel pipe is another major difference that the customers care about. As a matter of fact, the black steel pipe is usually much cheaper than that of the welded steel pipe, making it an ideal choice for those who want to cut off the cost. However, the black steel pipes need extra money to maintain and add to fittings. Thus, after carefully calculation, the welded steel pipe is much economical.

Advantages and Disadvantages of Welded Steel Pipe

The technology of welded steel pipe is continuous online production. So the thicker the wall thickness is, the greater the investment in the unit and welding equipment is, and welded steel pipe will have less economical efficiency and practical applicability. The wall thickness is thinner, its input-output ratio will be decreased accordingly. The process of the product determines its advantages and disadvantages. In general, the welded steel pipe with high precision, uniform wall thickness, high brightness of tube inside and outside (surface grade of steel plate determines the surface brightness of steel pipe), can be fixed length wilfully. Therefore, welded steel pipe reflects its economy and aesthetics in the high-precision, low-pressure fluid applications.
The production process of welded steel pipe is simple, the production efficiency is high, the cost is low, and develops rapidly. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. The pipe with larger diameter can be produced with the narrow billet and the pipe with different diameter can also be produced with the same width billets. However, compared with the same length of the straight pipe, the length of weld seam increased by 30% to 100%, and the production rate is low. Therefore, the pipes with smaller diameter are mostly used straight welding, the welded steel pipes with large diameter are mostly used spiral welding.

Source: China Welded Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (

(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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