Common surface defects of welded steel pipe

 Common surface defects of welded steel pipe:

(1) layered steel

Layered wall steel tube means the cross section is divided into two floors, exposed steel surface showing the hierarchical vertical cracks. Some exhibits inside and outside surfaces of steel recessed or raised locally, layered rendering suddenly raised, dents or warping in and out of the weld.

(2) sticky scar

Pipe sticky scar refers to internal and external surfaces of the massive steel focal adhesion plaques scar.

(3) holes

Pipe through the hole refers to a local steel tube bi holes exist.

(4) open welding

Welded steel pipe opening means through long cracks in steel welds or partial showing of.

(5) Local lap welding

Welded steel pipe refers to a partial outer surface of the steel pipe presents a partial arc weld.

(6) Welding ditch

Pipe welding groove is the outer surface of the steel pipe occurs through a long groove weld.

(7) the collapse of welding

Welded steel pipe collapse refers to the outer surface of the weld metal skeletons showing through a long trench, where the surface of the corresponding convex edges.

(8) pipe joints dislocation

Steel tube joint dislocation refers to the steel pipe weld, occurred the phenomenon of staggered up and down.

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Common Materials of ERW Welded Pipe

    Common materials for welded pipes are: Q235A, Q235C, Q235B, 16Mn, 20 #, Q345, L245, L290, X42, X46, X60, X80, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc.

    The blank used for welded steel pipe is steel plate or strip steel, which is divided into furnace welded pipe, electric resistance welded pipe and automatic arc welded pipe due to different welding processes. Because of its different welding forms, it is divided into two types: straight seam welded pipe and spiral welded pipe. Because of its end shape, it is divided into round welded pipe and special-shaped (square, flat, etc.) welded pipe. Welded pipes are divided into the following varieties due to their different materials and uses:

    GB / T3091-2008 (welded steel pipe for low-pressure fluid transportation): mainly used for conveying water, gas, air, oil and heating hot water or steam and other generally low-pressure fluid and other use pipes. Its representative material is: Q235A grade steel.

    GB / T14291-2006 (Welding Steel Pipe for Mine Fluid Transportation): Mainly used for straight seam welded steel pipes for mine pressure, drainage and shaft gas discharge. Its representative material is Q235A, B grade steel.

    GB / T12770-2002 (stainless steel welded steel pipe for mechanical structure): mainly used for machinery, automobiles, bicycles, furniture, hotel and restaurant decoration and other mechanical parts and structural parts. Its representative materials are 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb and so on.

    GB / T12771-1991 (stainless steel welded steel pipe for fluid transportation): mainly used to transport low-pressure corrosive media. Representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc.

    In addition, welded stainless steel pipes for decoration (GB / T 18705-2002), welded stainless steel pipes for building decoration (JG / T 3030-1995), and welded steel pipes for heat exchangers (YB4103-2000).

Welded steel pipe

    Welded steel pipes, also known as seam steel pipes, are generally welded from steel plates or steel strips. According to the surface treatment of the pipe, it is divided into two types: galvanized and non-galvanized. The galvanized surface is white, also called white iron pipe or galvanized steel pipe; the surface without galvanized is ordinary welded steel pipe, also called black iron pipe. Galvanized welded steel pipes are often used for pipelines that require relatively clean transportation media, such as domestic water, purified air, and instrument air. Non-galvanized welded steel pipes can be used for steam, gas, compressed air, and condensed water.

    According to user requirements, welded steel pipes can be divided into two types at the factory, one is pipe end with thread, and the other is pipe end without thread. The length of each welded steel pipe with thread at the pipe end is 4-9m, and the length of each welded steel pipe without thread is 4-12m.

    Welded steel pipes are divided into thin-walled steel pipes, thickened steel pipes, and ordinary steel pipes according to different wall thicknesses. Ordinary steel pipe is the most used on the process pipeline, and its test pressure is 2.0MPa. The test pressure of the thick steel pipe is 3.0 MPa.

    There are many connection methods for welded steel pipes, including screw connection, flange connection and welding. The flange connection is divided into threaded flange connection and welding flange connection, and the welding method is divided into gas welding and arc welding.

    The specifications of commonly used welded steel pipes range from 6 to 150 mm in nominal diameter.

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Application of High Pressure Boiler Tube In Life

　　The rapid development of the national economy has led to the improvement of people's living standards, which have contributed to the development of the power industry. The power industry is environmentally viable and in line with our sustainable development strategy. According to China's resources, China is still dominated by thermal power at this stage and for a long time to come.

　　It is said that the electric power industry should mention high-pressure boiler tubes. The boiler tubes are steels that are open at both ends and have a hollow section. The steel with a relatively large length and the surrounding area can be divided into seamless steel pipes and welded steel pipes according to the production method. Dimensions (such as outer diameter or side length) and wall thickness indicate a wide range of sizes, from small diameter capillaries to large diameter pipes up to several meters in diameter. Steel pipes can be used in pipelines, thermal equipment, machinery industry, petroleum geological exploration, containers, chemical industry and special applications. In general, the high-pressure boiler tube is also a kind of seamless steel pipe, and its production process is the same as that of the seamless steel pipe. However, high-pressure boiler tubes are important components of power station boilers, used to manufacture high-pressure and ultra-high-pressure power station boilers, and are used to build large-scale thermal power plants.

　　Therefore, high-pressure boiler tubes are often in a high-temperature, high-pressure environment, so the requirements for his raw material billets are required. It is very strict and requires high durability and high corrosion resistance, oxidation resistance, and good stability.This will require you to shop around when you choose a high-pressure boiler tube, compare the price, but also to compare the quality.

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Manufacturers and suppliers of welded steel tubes

　　Tianjin Xinyue Steel Group as a welded steel pipe supplier in China, offering the best price of cold drawn welded pipe is our competitive advantages. we can offer all kinds of cold drawn welded pipe in stock.

　　The cold drawn welded steel pipe term is often used to describe special products from a processing technology of welded steel pipe. Cold drawn welded pipe has accurate specification, good concentration, uniform wall thickness, diameter and mechanical properties, good degree of hardness, resistance to bending and tensile properties, high standard of surface polishing and ensure the integrity of the welding. This kind of steel pipe still need further fine processing before using. Cold drawn welded steel pipe need to plaquette, then Individuation to shaft for drawing again. We can produce a variety of specifications of the finished tube by this way and may use several kinds of metal stamping and shaft during period.

　　Cold drawn welded(DOM) technology is mainly used for mass production of the pipe of mechanical equipment (such as the hydraulic system) and solid core rod with the diameter close to the ideal inner diameter. If you need cold drawn welded steel pipe, you can contact us at any time, we will provide you the best price of cold drawn welded pipe.

Magnetism of carbon steel tube

　　Residual magnetism causes and impact on quality of welding

　　When the gas pipeline construction and repair welding operations, sometimes magnetic blow phenomena affect the welding process. Forming a magnetic blow is the result of the presence of residual magnetism in the pipe metal. Typically, the magnetic induction and magnetic remanence divided into two processes. Magnetic induction in plants often produce tube links, such as: metal smelting, using electromagnetic crane for loading and unloading, pipe parked or garaged in a strong magnetic field, the magnetization is completed nondestructive inspection method, the pipe is placed close to power lines and so strong. Processes often produce magnetic welding operations during the assembly and the use of a magnetic holder, fixture and took DC welding pipes, such as: prolonged contact is connected to a DC power supply electric wire, bare wire segment or short-circuit pipe welding clamp and so on.

　　When welding with magnetic steel, often difficult to see the arc ignition, combustion undermine the stability of the arc, the arc of the deviation, the liquid metal and slag melt the spill from the weld pool in a magnetic field. In order to stabilize the welding process and improve the quality of the welded joint, the steel is magnetized to demagnetized before welding. It should be noted, to be welded steel pipe is difficult to achieve full demagnetization. Therefore, when the remanence is insufficient to affect the quality of welding, it allows welding.

　　Magnetic elimination of carbon steel pipe process

　　1 to determine the size and direction of the pipe left field;

　　2 Select the degaussing method, system diagrams and technical means;

　　3 butt welded steel pipe or at the degaussing degaussing with the selected method;

　　4 After checking the amount of residual magnetism after degaussing, to see if it meets the requirements.

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.

Pipeline inspection of welded steel pipe

　　Welded steel pipe at the factory to go through rigorous testing to ensure the quality of welded compliance standards and user requirements. Pipe inspection items generally include: appearance quality factory inspection project, straightness, dimensions, and other types of weld quality inspection items (flattening, flaring, bending, etc.). Welded pipe surface quality and straightness inspection by a full-time quality inspector confirmed finishing process pipe segment using visual way, the implementation of the detection test dimensions available random sampling method, and the weld quality inspection shall be made on special equipment by root on line. This article focuses on online testing of the weld. At present, about our national standards, testing methods available weld pipe hydrostatic testing, ultrasonic testing, eddy current testing in any way.

　　Hydrostatic test is the most common, the most direct and reliable weld line inspection

　　Measured way, in a variety of hydraulic test machine. When the pressure test, through the first low-pressure water, filled the whole steel pipe to make the air side by side, and then to test pressure specified by the pressurized way, and to stabilize the prescribed time, when there is no pipe welds and around wet, spray, leakage or permanent deformation is considered qualified.

　　When the metal by an alternating magnetic field is induced metal surface

　　Eddy currents; when the presence of the metal surface defects, since the impedance increases, the eddy current value becomes smaller; and when no defect of a metallic material, the value of the stable vortex; size of the power according to the eddy current loss, can be characterized metals whether the surface defects.

　　Ultrasonic wave propagation in the process, will have a reflection on the media surface.

　　If there is a crack pipe welds, weld, false welding, lap welding defects such as acoustic impedance will change significantly, so that ultrasonic generating different reflection, through a dedicated instrument will be identified to achieve the purpose of flaw detection. The main steel tube ultrasonic flaw detection are: rotating the probe, steel straight forward; probe fixed, steel rotating forward; steel rotating probe straight forward three forms, in the production of different pipe diameter in both applications.

Weld hole prevention measures

　　It is well known that there are many types of welded steel pipes. There are always seamless steel pipes and straight seam steel pipes(LSAW), while straight seam steel pipes have weld seams, and weld seams will produce pores under certain conditions. Generally the factors causing the pores in the weld are: moisture, dirt, scale and iron filings in the flux, welding composition and thickness, steel surface quality and steel edge treatment, welding process and steel tube forming process. The weld hole of the welded pipe not only affects the tightness of the pipe weld, but also causes the pipe to leak, and it will become the induction point of corrosion, which seriously reduces the weld strength and toughness.

　　Steel surface treatment: in order to avoid the inclusion of iron oxide and other impurities in the unwinding and unwinding, a plate cleaning device should be provided.

　　Steel sheet edge treatment: rust and burr removal devices should be installed on the side of the steel plate to reduce the possibility of generating air holes. The position of the cleaning device is preferably installed after the edge milling machine and the disc cutter. The structure of the device is a movable wire wheel with two adjustable positions on one side, and the upper and lower sides of the plate are pressed.

　　Weld appearance: the forming coefficient of the weld is too small, the shape of the weld is narrow and deep, and the gas and inclusions do not easily float out, and the pores and slag are easily formed. Generally, the weld bead forming coefficient is controlled at 1.3-1.5, the thick-walled welded pipe takes the maximum value, and the thin-walled pipe takes the minimum value.

　　Reduce the secondary magnetic field: in order to reduce the influence of magnetic partial blow, the connection position of the welding cable on the workpiece should be kept away from the welding terminal only, and the partial welding magnetic cable can be prevented from generating a secondary magnetic field on the workpiece.

　　Process aspect: the welding speed or current should be appropriately reduced to delay the crystallization rate of the weld pool metal to facilitate gas escape. At the same time, if the strip delivery position is unstable, adjustment should be made in time to prevent fine adjustment of the front axle or rear. The bridge remains shaped, causing gas to escape.

　　Flux composition: when the solder contains an appropriate amount of CaF2 and SiO2, it absorbs a large amount of H2 and generates HF which is highly stable and insoluble in the liquid metal, thereby preventing the formation of hydrogen pores. The deposition thickness of the flux is generally 25-45mm, the flux particle size is large, the density is small, the stacking thickness takes the maximum value, and the minimum value is taken; the large current, the low welding speed stacking thickness takes the maximum value, and the minimum value, in addition, the summer or the air When the humidity is high, the recovered flux should be dried before use.

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Welded steel pipe defect

　　Welded steel pipe production process is a steel sheet,strip,and other various molding methods using the straight press roll helical direction curling into a desired cross-sectional shape,and then by means of heart,prssure,different methods of welding weld weld together to obtain steel.Therefore,defects in the welded steel pipe is divided into two parts:the steel base material defects and weld defects.

　　1.Steel base material defect

　　The sheet material defects after rolling and other processes,most of planar,parallel to the surface;their main weakness delamination,cracks,folds,etc.,which is the most common layered internal defects.Stratification will produce a variety of cracks when the tensile stress perpendicular to the surface of the sheet by the hierarchical will seriously affect the strength of the steel pipe,it is not allowed defects.

　　2.Weld defects

　　Weld defects refers to defect during welding or after welding resulting in the weld is divided into cracks,proes,slag,incomplete penetration,incomplete fusion,undercut weld defects.Intensive weld porosity,slag,etc.a dense three-dimensional defects,cracks,lack of fusion and other defects in the case of the flat,great harm.Strip slag.

Do you know how many kinds of welded steel pipes there are?

　　What is welded steel pipe? Just as its name implies, welded steel pipe is manufactured by steel belt or steel plate bending the barrel, and then using flux to weld, there is a weld seam on the pipe. Common types of welded steel pipe are ERW steel pipe, LSAW steel pipe, SSAW steel pipe, and so on.

　　General steel pipe is used to transport low-pressure fluid and easy to weld the other soft steel. Usually, the length of the delivery of 4-10m is actually different, according to the provisions of the wall thickness the pipe has two kinds of steel, the spiral seam and the straight seam.

　　SSAW steel pipe adopts the low carbon construction steel strip or low alloy structural steel strip to roll into a tube, and then weld together, to product large diameter SSAW steel pipe. SSAW steel pipe is mainly used for oil and natural gas pipeline, SSAW steel pipe adopts single-sided welding and double-sided welding. Welded steel pipe should ensure that water pressure test, weld tensile strength and cold bending performance can meet the requirements.

　　LSAW steel pipe is made by using strip steel as raw materials and doing longitudinal welded in the high-frequency welding equipment(hence the name due to the weld forms a straight line). In accordance with the use of different, there are different production process (can be divided into scaffolding tube, fluid tube, wire casing, bracket tube, fence tube, etc.).

　　Another commonly-used kind of welded steel pipe is ERW steel pipe. ERW steel pipe is the abbreviation Electric Resistance Welded Pipes. ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes. ERW steel pipe is manufactured by rolling metal and then welding it longitudinally across its length. ERW steel pipes are welded longitudinally, manufactured from Strip / Coil and can be manufactured up to 24”OD. ERW pipe cold formed from a ribbon of steel pulled through a series of rollers and formed into a tube which is fused through a electric charge.

　　Welded steel pipe is the main product of Prime Steel Pipe, as the leading welded steel pipe manufacturer and exporter, we provide a large number of ERW steel pipe, LSAW steel pipe, SSAW steel pipe and other welded steel pipe for sale. More products details please click the hyperlink.

Seamless steel tube as the advantages of pipeline transport materials

　　According to the size of the caliber, there is also a clear distinction between the use of seamless steel tubes. From the current market point of view, there are more than ten sizes of seamless steel tubes. In order to meet the needs of the market, its production scale is still In the continuous expansion, talking about this type of pipe material, more is used as a material for pipe transportation, so more is the use of large-diameter seamless steel pipes, such large-sized steel pipes, Many problems can be avoided during transportation.

　　Compared with ordinary welded steel pipes, the safety of seamless steel pipes used as pipe transportation materials is very high, which is one of the advantages of this type of pipe material. The thickness of the pipe wall is also different depending on the specific application. If it is used as a material for transporting oil and natural gas, the pipe wall will generally be thicker, which can effectively avoid the transportation process. In the case of a leak that occurs, this type of pipe material is constantly evolving at the level of the manufacturing process.

　　Seamless steel tubes are highly utilized in the market and are also widely used in the industrial sector. This type of piping material has a high market price/performance ratio and is therefore very popular in the market. Among the many steel pipe materials, the advantages of seamless steel pipe are obvious, and more are used as materials for fluid and gas transportation. Pipe transportation is an environmentally intensive transportation mode. In modern society, pipe belt transportation It is already a very common way of transporting, so the materials needed for pipeline transportation also get a good market space.

　　If it is used as a material for pipeline transportation, it is necessary to consider the applicability of such pipeline material before exiting. It is necessary to consider from the viewpoint of mechanical properties to see if this type of pipeline material meets the actual requirements. It is also used in the construction sector. The transportation of groundwater also requires the use of seamless steel pipes.

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The strip width deviation affects the quality of welded steel tubes

　　Frequency welded pipe production process, affecting the quality of the elements have more than one pipe, the main raw materials, welding technology and roll count which is beginning to adjust.

　　Key to look at raw geometric dimensions. Strip geometry affect the quality of the steel strip width when less than the allowable deviation, the extrusion pressure welded steel pipe is reduced, making the pipe weld welding is not strong, cracks or open tube. When the width of the strip is greater than the tolerance, the pressing force is increased when the welded steel pipe, steel pipe welds appear beak, lap welding and other welding defects or burrs. Therefore, the fluctuation width of the strip, not only affects the accuracy of the outside diameter of the steel pipe, but also seriously affect the surface quality of the steel pipe.

　　Requirements for the same section thickness difference does not exceed the predetermined value of the steel pipe, which requires a high degree of uniformity of the wall thickness of steel pipe, fluctuations in the thickness of the strip, the same volume will be transferred to the wall thickness of the permissible value of finished steel strip thickness difference exceeds the difference so that a large number of steel thickness exceeds the allowable deviation and sentenced to waste. Fluctuations in the thickness of the finished steel thickness only affects the accuracy. Meanwhile, since the strip thickness varies, the steel pipe during welding, extrusion pressure and welding temperature instability, resulting in unstable weld quality steel welding.

　　In addition, since the internal steel sandwich material defects exist, impurities, such as trachoma, is a major factor affecting the quality of steel. Therefore, before steel welding, to check each roll strip surface quality and geometry of the strip quality does not meet standards, not production, so as to avoid unnecessary losses.

Production and requirement of welded steel pipe

　　Welded steel pipe, also called steel flower welded pipes, is a steel pipe made by welding a steel plate or a steel strip after being crimped. The welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and low equipment investment, but the general strength is lower than that of seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technology, the quality of welded joints has been continuously improved, the variety specifications of welded steel pipes have been increasing, and more and more fields have replaced seamless steel pipe.

　　Welded steel pipes are divided into straight welded pipes and spiral welded pipes in the form of welds. Straight seam welded pipe has simple production process, high production efficiency, low cost and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight welded pipe. It is possible to produce a welded pipe with a larger diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter with a blank of the same width. However, compared with the straight pipe of the same length, the weld length is increased by 30 to 100%, and the production speed is low. Therefore, the smaller diameter welded pipes are mostly straight seam welded, and the large diameter welded pipes are mostly spiral welded.

　　1. Welded steel pipes for low-pressure fluid transportation are also called general welded pipes, commonly known as black pipes. It is a welded steel pipe for conveying general low pressure fluids such as water, gas, air, oil and heating steam and other purposes. The thickness of the steel pipe is divided into ordinary steel pipe and thick steel pipe; the pipe end form is divided into non-threaded steel pipe (light pipe) and threaded steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is an approximation of the inner diameter. It is customary to use inches, such as 11/2. The welded steel pipe for low-pressure fluid transportation is mainly used as a raw pipe for galvanized welded steel pipe for low-pressure fluid transportation, in addition to being directly used for conveying fluid.

　　2. Galvanized welded steel pipes for low-pressure fluid transportation are also called galvanized electric welded steel pipes, commonly known as white pipes. It is a hot dip galvanizing (furnace welding or electric welding) steel pipe for conveying water, gas, air, oil and general lower pressure fluids such as heating, steam and warm water. The thickness of the steel pipe is divided into ordinary galvanized steel pipe and thick galvanized steel pipe; the connection end form is divided into non-thread galvanized steel pipe and threaded galvanized steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is an approximation of the inner diameter.

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Steel Pipe Uses in Gas Project

　　Steel pipe is the most widely used gas pipe project. Its main advantages are: high strength, good toughness, bearing stress, impact resistance and tight, good plasticity, easy welding and thermal processing, the wall thickness is thinner, saving metal. But its poor corrosion resistance, need to have proper anti-corrosion measures.

　　Steel pipes for gas pipelines in the main city of seamless and welded steel pipe in two categories. High strength seamless steel pipe, but limit the production process and costs by generally small diameter steel pipe DN200 below. More types of welded steel pipes, welding can be divided by straight seam welded steel pipes and spiral welded steel pipe types. Among them, straight seam welded steel pipe (hereinafter referred to as straight seam pipe) also includes LSAW steel pipe and high frequency resistance welding (ERW) steel pipe and other types. Spiral welded steel pipe (ssaw steel pipe) is a spiral seam double submerged arc welded (HSAW) pipe.

　　The straight seam and spiral pipe manufacturing process are compared, the former has the advantage of:

　　① spiral pipe manufacturing process to determine their residual stress is greater than the straight seam pipe, straight seam pipe with the overall result of expanding process, residual stress close to zero, while the spiral can not do this;

　　② spiral weld wrong side mostly in the range of 1.1 ~ 1.2mm, the standard requires the amount of the wrong side of the wall thickness to less than 10% for thin-walled tubes, the wrong side is difficult to meet the standard requirements, and straight seam pipe does not exist This problem;

　　③ Compared with straight seam pipe, spiral weld line flow is poor, serious stress concentration;

　　④ coil heat affected zone is greater than the straight seam pipe, and pipe heat affected zone is the key to quality;

　　⑤ spiral geometry accuracy, to the construction site, as counterpart, welding bring some difficulties.

Welded steel tube used for conveying low - pressure fluid

　　Welded tube is using the materials, such as steel belt or plate stuff, as the steel pipe joint on the surface, which makes the welded can bend into round or triangle shape. That makes the tube shape. Welded steel pipe is formed in 1.0m for the pipe diameter and more than 10mm thick from the steel plate. In the industrial field, we can see lots of application of this welded steel pipe is being used, such as shipment delivery and the basic structural materials for building and factories, etc. Therefore, lots of customers can are satisfied in meeting this pipe. They can ask for special requirements on the quality, specifications and even the size. More originally, we are using this pipe in transporting gas, liquid and even the heating. We are using them in delivering water through the country and providing necessity for the resident.

　　We can divide the welded steel pipe into three main types, the high, the low and the gas tube. Those are evidenced by their different methods. Moreover, we still can see some minority types, such as the furnace pipe.

　　Making the welded tubes is simpler than other types, like the seamless steel pipes and black steel pipes. Thereby, the manufacturer has high efficiency. Since one hundred year ago, the development of the kind of pipes makes it possible to improve its quality and specifications like the lengths and diameters. Flat products such as plate and sheet are the original materials in making welded tubes. After certain degree compression and temperature, it can make it into desired shape. Basically, manufacturers would like to make it round shape, since it is good for transporting, especially for those low-temperature liquid. Once this outer shape is made, weld joint are used to combine each part together. High energy are needed at the same time, since this process need power to squeeze and form. Customers and buyers are provided more choices as the increasing number of pipes. According to different making process, this type can be divided into two main forms---the spiral welded pipe and longitudinal pipe. For the advantages, simple procedure is the first one, then various types are the second since customers can choose their specific types. What's more, equipment investment is quite low, while the general strength less than seamless steel tubes.

　　In the case of high pressure and vibration, steel pipe are especially helpful since their resistance. They can resist rust, corrosion and fire and therefore, apart from carrying liquid and gas, they can also be applied for fire sprinkler system. Welding steel pipe is under the imposition of government and the quality of the pipe must meet the specified standard. Different pipeline application has different regulations; you need to apply the stringent rules to make sure a safe criterion. Qualified steel pipe works wonder and save trouble to the project and less maintenance in later use. We suggest all the customers to take every important details into consideration before purchasing the pipe.

Technical development of welded steel tubes

　　Nearly all pipe making involves the welding process. The techniques in dealing with this procedure in most cases determine the difference between a hack job and good craftsmanship. The steels used in the making of welded steel pipe are far more sophisticated than those in the 1980s and 1990s. More kinds of steel alloys marked with outstanding physical and chemical properties have been invented and applied in a whole range of projects. For example, a stainless steel alloy is primarily made of iron with a substantial amount of chromium and nickel added during the alloying process. The most notable type of corrosion-resistant stainless steel alloy is widely used by architects to be applied in environments with high moisture. In addition, the heat treatments and the melting process have been dramatically upgraded. Thanks to the technological development of welded steel pipe, steel pipe manufacturers are capable of creating development welded steel pipes that are precisely crafted to meet customers' demands.

　　There are various kinds of welded steel pipe. ERW steel pipes are generally cold formed and can be made by the means of spot welding and seam welding in a variety of lengths and thickness. As a matter of fact, both methods involve the use of electrical energies to hold the melting steel together, hence the name of ERW steel pipes. Besides, such factors as the heating temperatures, the chemical compositions of electrode geometry, and the physical properties of the steel all have certain influence on the welding results. Thanks to the versatility of the ERW steel pipes, they are widely used in the underground piping projects and you may also find ERW steel pipes in such places as warehouses and hospitals.

　　On the other hand, in comparison with coating steel pipe, fusion welded steel pipes have different manufacturing methods and applications. Generally speaking, fusion welded steel pipes are often used to transport fluids such as water in agricultural projects and chemical plants. Made of coiled steel that is joined one after another, fusion welded steel pipes are sent into a furnace to get welded. The good news is that fusion welded steel pipes can be manufactured from the mixture of steel alloy and a wide range of less expensive metals, depending on the customers' requirements. What is more, marked with appealing aesthetic features, spiral welded steel pipes are frequently used in construction projects to add to the geometric styles of the buildings. And it is relatively easy to install spiral welded steel pipes because thanks to the curvy shapes, less joints and hangers are needed in the installation. Moreover, with a smooth interior, the spiral welded steel pipes can also be used to transport gas or fluids as the special shape can helps reduce leakage and relieve the pressure on the pipe walls. In chemical production practice, spiral welded steel pipes not only helps to reduce the amount of toxic pollutants but also collects the useful byproducts.

A new method for measuring the wall thickness of welded steel tubes

　　This device consists of a measuring head of laser ultrasonic measuring equipment, a motivating laser, an irradiating laser and a convergence optical element that is used to collect lights reflected from the surface of the pipe to the measuring head. The important mass parameter for pipe production is wall thickness. So it is needed to measure and monitor its parameter in the course of pipe production. You should create a laser ultrasonic survey to measure the wall thickness of the welded steel pipe .It is a measurement method which is based on pulse echo principle to ensure the wall thickness through measuring the spreading time of ultrasonic pulse.

　　This device uses a motivating laser that will lead ultrasonic pulse into the surface of the pipe. And then this ultrasonic pulse spreads into the pipe and reflects on the inner wall. And we could measure the signal that return to the outer wall through putting an irradiating laser aiming to the surface of the pipe. This reflected signal will be sent into an interferometer where there is a homocentric interferometer. A analysis and process device makes sure the time difference between input ultrasonic signals and reflected ultrasonic signals to figure out the wall thickness value under the circumstances of having known the spreading speed in the pipe.

　　In order to make this device measure the wall thickness of welded steel pipe accurately and stably, it is necessary to make laser ultrasonic measurement device work under the best working condition. And its prerequisite is that the light beam sent out by motivating laser and the light beam sent out from the irradiating laser must meet on the assigned place. However, first of all, we must try our best to keep accurately the distance between measuring pipe and measuring head. In addition, practices have proved that it is hard to ensure the best working condition under above environment situation, especially in the process of rolling, impossible to adjust the laser ultrasonic measurement device. And this can only be made through the regular control of the device. Otherwise, the distance between measuring head and the surface of the pipe of the laser ultrasonic measurement device must be kept in an ideal index value to make sure the reflected laser light from the surface of the pipe could best input the measurement device.

　　Set at least two light resources that send the same one bundling light and are fixed on the different places of the measurement head. And at least two light resources can be foxed on the measuring head like this and be corrected direction. Namely when there is a beforehand distance of pipe and measuring head, the bundling lights from these two light resources will cross on the surface of the welded steel pipe. No matter how long the distance between the head and the surface, you can easily measure with the method above. Thus, it can be sure that the laser ultrasonic measurement device has best working condition under the rough rolling condition, enhancing the productivity as well as quality of the welded steel pipe.

The Common Types of Welded Steel Pipes

　　Welded steel pipe is bent with steel or steel plate is round, square and other shapes and then welded into the surface of the seam with the steel pipe. Common types of welded steel pipe are the following:

　　General pipe, used to transport low-pressure fluid, easy to weld the other soft steel manufacturing. Steel pipe to pipe and thick steel pipe specifications with the nominal mouth of the water pressure, bending, flattening and other experiments, the surface quality has certain requirements, usually the length of the delivery of 4-10m is actually different, the pipe according to the provisions of the wall thickness Two kinds of steel, according to the thread and no thread two.

　　Roller, for belt conveyor roller welding steel pipe, the general water pressure and flattening test.

　　Metric welded pipe, specifications with a seamless tube form, with ordinary carbon steel, high quality carbon steel or Cape can be low-alloy steel tropical, cold belt welding, or with a tropical welding and then made by cold dial method.

　　Spiral welded pipe, is the low carbon carbon steel strip according to a structural steel or low alloy structure of the helix angle (called forming angle) rolled into a tube, and then welded together made of pipe, strip production of large diameter Of the steel pipe. Spiral welded pipe is mainly used for oil and natural gas pipeline, spiral welded pipe with single-sided welding and double-sided welding, welded pipe should ensure that water pressure test, weld tensile strength and cold bending performance to meet the requirements.

　　Metric pipe is divided into ordinary and thin wall, commonly used as structural parts, such as transmission shaft, or conveying fluid, thin wall used to produce furniture, lamps, etc., to ensure the strength of steel and bending test.

Welded Steel Pipe for Low Pressure Fluid

　　Welded steel pipe for low pressure fluid (GB/T3092-1993), also known as general welded pipe, commonly known as the clarined,which used for conveying water, gas, air, oil and steam heating and other general low pressure fluid. steel pipe can be divided into ordinary steel pipe and thicken steel pipe according to the wall thickness. Specifications of steel pipe with nominal diameter (mm) that the nominal diameter is the diameter of the approximation. Customarily used in inches. Welded steel pipe for low pressure fluid directly is used for conveying fluids, but also a lot for low-pressure fluid the original tube of galvanized steel pipes.

　　Galvanized welded steel pipe for low pressure fluid (GB/T3091-1993), also known as galvanized welded steel pipe, commonly known as white tube, which is used for conveying water, gas, air, oil and steam heating, warm water and other fluids, or other general purpose low-pressure hot-dip galvanized welding (soldering or welding furnace) steel pipe. steel pipe can be divided into ordinary galvanized steel pipe and thicken galvanized steel pipe according to the wall thickness,and according to the pipe form,it be divided into without threaded galvanized steel pipe and threaded galvanized steel pipe. Specifications of steel pipe with nominal diameter (mm) that the nominal diameter is the diameter of the approximation. Customarily used in inches.

　　General low-frequency fluid transport with spiral seam welded steel pipe (SY5039-83) is a hot-rolled steel strip for the tube volume, temperature often spiral shape, high frequency welding lap welding method for general low pressure liquid delivery Spiral high-frequency welded steel pipe.

　　General low pressure liquid delivery spiral submerged arc welded pipe (SY5037-83) is a hot-rolled steel strip for the tube volume, temperature often spiral shape, using single-sided or double-sided automatic submerged arc welding method as for water , gas, air and steam is generally low pressure liquid delivery such as submerged arc welding steel pipes.