What is a spiral steel pipe?

What is a spiral steel pipe?
Spiral steel pipe is made by steel coil, extrusion forming under the normal temperature, then taken the technology of double wire and double-faced submerged-arc welded.
Spiral steel pipe, also known as spiral or helix spiral steel pipe, is a low-carbon steel or low-alloy structural steel strip at a certain helix angle (called molding angle) rolled into a tube, and the tube is made of welded joints It can be produced with a narrow strip of large diameter pipe.
During molding process of spiral welded steel pipe, steel plate has uniform deformation and light residual stress, thus the surface has no scratches. Spiral steel pipe has more flexible thicknesses and diameters, especially in making high-grade thick pipes with small or medium aperture, these techniques has incomparable advantages in satisfying your needs.

 201611292245327804629 - What is a spiral steel pipe?

1. unwinding board probe: After entering the unwinding plate production line, the first full-board ultrasonic testing.
2. Leveling Milling: The flat steel anvil machine so that the original curl, and then through the edge milling machine for two-sided steel milling, so as to meet the requirements of the plate width, plate edge parallelism and groove shape.
3. shear molding: the steel plate production line along the outer edge of the spiral curl into a tube.
4. butt cut: double-sided submerged arc welding using advanced technology to pre-welding, internal welding, outside welding. Ion foot cut to specification length welded spiral pipe use and so on.
5. visual inspection: by professional and technical personnel to some of the basic parameters to be checked.
6. The ultrasonic flaw detection: internal and external weld and weld on both sides of the base material 100% inspection.
7. X-ray detection: internal and external welds 100% X-ray industrial TV check image processing system to ensure that the use of detection sensitivity.
8. The pressure test: the spiral steel pipe hydrostatic testing machine-by-root test to ensure that the pressure test pipe meet the required standards.
9. chamfering flat head: spiral steel pipe inspection carried out after the pipe end processing, to meet the requirements of the pipe end beveling size
10. Final inspection: ultrasonic and X-ray detection again and spiral steel pipe ends magnetic particle inspection, check if there are problems and welding pipe ends defects.
11. oiled marking: spiral steel pipe after passing were oiled to prevent corrosion, and according to user requirements for marking.

Eliminating the magnetic field generated around the spiral steel pipe

Reasons for the magnetic field of spiral steel pipe
In the welding process, welding by DC welding, in welding line, and the position of the welding head due to the high current, resulting in a strong magnetic field, pipe body under the action of magnetic field, magnetic moment or tend to obtain and external magnetic field in the same direction are arranged. When the welding end, magnetic field gradually decreased till disappeared, due to the hysteresis phenomenon, in the tube body and residual magnetic flux density, this is what we say normally remanence.

The harm of spiral steel tube magnetic field
Existent remanent magnetization, the image intensifier and the electron beam deflection and X-ray industrial TV image system produced the “s” type distortion, influence porosity, slag and other natural defects, especially the detection rate of incomplete penetration, cracks and other linear natural defects.
With the change and improve X ray image intensifier TV system pipeline steel grade, the remanence was particularly prominent.
Remanence existence, ring butt in the pipeline, will produce the phenomenon of partial arc, welding quality.
Remanence have seriously affected the quality of construction
The AC degaussing method of spiral pipe is the most common method:
1, with the coil around the outside of the steel tube, to the coil through the alternating current, slowly reduce the current of alternating current, until reduced to zero. Degaussing results: don’t change the physical properties of spiral steel pipe, however, once again encountered the external magnetic field, spiral steel tube also is magnetized.
2, through the heat treatment process, can be more thoroughly the degaussing, however, after degaussing, hardness and rigidity of the spiral pipe will change, encountered again in the future the external magnetic field, plus the magnetic field is removed, the steel pipe can basically there is no residual magnetism.
3, heat treatment process, is probably: oxygen free heating to a certain temperature, and then, with 72 hours slowly cooling to room temperature.

Analysis of the causes of the wrong side of spiral steel pipe

Spiral steel pipe in the production process if the production process is unreasonable, machine parameter settings shall be deemed to occur deviation phenomenon, especially large diameter spiral steel pipe, which is often said the wrong side of the phenomenon.
After spiral steel pipe wrong side analysis of the causes produce the wrong side is very necessary, the following is a common cause of generating the wrong side.
1, strip steel camber is caused by the wrong side of the most important factors. In forming the spiral welded pipe, steel strip camber angle will constantly change shape, leading to changes in the weld gap, resulting in open seam, wrong side or even take sides.
2, strip head and tail butt welding weld reinforcement is large, when the over-molding, if not handled properly, likely to cause greater wrong side.
3, due to the poor is not trimming the strip head and tail shape and size precision, easy to cause docking strip hard bend caused by the wrong side.
4, the strip edges in poor condition is another important reason for the wrong side.
Therefore, the observation strip coil-camber situations after, by controlling the vertical rolls so that the disc can be cut and removal of part of camber angle forming the continuous control and corrective camber of the strip is the reduction in the production process effective way of generating the wrong side.
For the production of spiral steel pipe processing program has been completed on the wrong side as follows:
1, the position of the wrong side of the polished, then welding
2, if a situation occurs frequently on the wrong side, you can replace the equipment.

Connecting method of large diameter spiral steel pipe

The most common way to connect large diameter spiral steel pipe is to weld, but in some projects, it is often used in the form of screw connection, flange connection, socket connection and groove connection.
Welding and flange connection - What is a spiral steel pipe?
Welding and flange connection

Connection features
Welding, flange connection belongs to l spiral steel pipe traditional pipe connection, in safety, sealing performance, cost of space, the repair efficiency has far cannot satisfy the market demand.
Grooved pipe connection - What is a spiral steel pipe?
Grooved pipe connection

Groove pipe connection technology is also called the clamp connection technology, has become the current first technology of liquid, gas pipeline connections, although the technology in domestic development time later than abroad, but because of its advanced technology, was received by the domestic market soon. The application of the grooved pipe connection technology, make complex pipe connection process becomes simple, fast and convenient. The pipeline connection technology major strides forward.
Groove connection pipe fittings include two categories of products: (1) connecting sealing effect of pipe fittings with rigid joints, flexible joints, mechanical tee and the groove of the flange; (2) connect the transition role of pipe elbow, tee, four-way, reducer, and blind plate, spiral welded pipe, etc. Connecting sealing effect of groove connection pipe fittings mainly has three parts: the sealing rubber ring and clamp and locking bolt. Is located in the inner lining of the rubber seal on the outer edge of the connected pipes, and in conformity with the advance of rolled groove, and buckle on the outside of the rubber ring clamp, then with two bolts. Due to the rubber sealing ring and clamp adopting special seal structure design, make the groove fittings with good sealing, and with the increasing of inner fluid pressure, the sealing enhanced accordingly.
Groove connection makes the pipe connection operation is simple, is advantageous to the construction safety, the system has good stability, easy maintenance, save work time, so has the good economic efficiency. The clamp connection, although the clamp single accessories price is higher, but the whole pipeline installation of comprehensive benefit is higher than the flange connection.

Suitable for liquid, gas pipe connection
Pipe clamps connection - What is a spiral steel pipe?
Pipe clamps connection

Connection features
Coupling connection as an advanced way of pipe connection, which can be set can also be buried Ming, the joint rigidity, also has a flexible joint. Therefore has wide scope of application.

Scope of application
Points: according to the system can be used for fire water system, air conditioning hot and cold water system, water supply system, petroleum and chemical piping systems, thermoelectric and military industry pipeline system and sewage pipe system, etc.
According to the points of piping material: can be used to connect steel pipe, steel pipe, stainless steel pipe, plastic pipe, ductile iron pipe, plastic pipe and steel pipe with thick wall joints and flange joint soft valve.

Classes of spiral steel pipe
1, Low pressure fluid pipe welded steel pipe is generally known, commonly known as the clarinet. Welded steel pipes for conveying water, gas, air, oil, and other general low pressure steam heating fluid and other purposes. Wall thickness of pipe into ordinary steel and thicker steel; take over the side into the form does not with steel pipes and tubes with steel. Pipe specifications with nominal diameter (mm), said nominal diameter is the diameter of the approximation. Traditionally used in inches. Low pressure fluid welded steel pipe for conveying fluids in addition to direct, but also a large number of low pressure fluid used galvanized welded the original steel pipe. 
2, Low pressure fluid galvanized welded steel pipes, also known as galvanized welded steel pipes, commonly known as white tube. Hot-dip galvanized welded steel pipe used for conveying water, gas, air, oil and steam heating, warm water, such as generally low pressure fluid or other purposes. Wall thickness of pipe into ordinary galvanized steel 
and thick galvanized steel; pipe ends into the form of non-threaded galvanized steel pipe and threaded galvanized steel pipe. Pipe specifications with nominal diameter, said nominal diameter is the diameter of the approximation. Traditionally commonly expressed in inches, such as 11/2 and so on. 
3, Ordinary carbon steel wire casing is the industrial and civil construction, installation of machinery and equipment for the protection of electrical installation works top steel wire. 
4, Straight seam welded steel pipe and steel pipe is parallel to the longitudinal weld pipe. Usually divided into metric welded steel pipe, welded tube, transformer cooling pipes and so on. 
5, Pressurized liquid delivery spiral submerged arc welded pipe is hot-rolled steel strip coils for the tube, often warm spiral shape, with double-sided submerged arc welding method for spiral seam steel pressure fluid transfer. Strong pressure steel, welding performance is good, through a variety of rigorous scientific inspection and testing trial, the use of safe and reliable. Pipe diameter, high transmission efficiency, and can save the laying of pipeline investments. Mainly used for oil pipelines, natural gas. 
6, The pressure transmission fluid with high-frequency spiral welded steel pipe is hot-rolled steel strip coils for the tube, often warm spiral shape, lap welding method using high-frequency welding, high frequency spiral seam for pressure fluid transfer welded steel pipe. Strong pressure steel, plastic, and easy welding and machining molding; through 
from a variety of rigorous and scientific inspection and testing, safety and reliability, pipe diameter, high transmission efficiency, and save the laying of pipeline investments. Mainly used for laying to transport oil, natural gas and other pipelines. 
7, The general low pressure liquid delivery spiral submerged arc welded pipe is hot-rolled steel strip coils for the tube, often warm spiral shape, using double-sided or single-sided automatic submerged arc welded into the legal system for water, gas, air and steam low pressure liquid delivery SAW pipe. 
8, The general low pressure liquid delivery spiral seam high frequency welded steel pipe is hot-rolled steel strip coils for the tube, often warm spiral shape, using high frequency lap welding method for general low pressure liquid delivery spiral seam high frequency welded steel pipe. 
9, Spiral welded steel pipe pile is hot-rolled steel strip coils for the tube, often warm spiral shape, using double-sided submerged arc welding or high frequency welding made for civil engineering structures, piers, bridges and other infrastructure pile with steel pipe. 

Characteristics of spiral steel pipe: Longitudinal production process is simple, high efficiency, low cost, rapid development. Spiral Welded Longitudinal generally higher than that, can narrow the billet production of large diameter pipe, you can also use the same width of the billet production of different pipe diameters. But compared with the same length of straight seam pipe, weld length of 30 to 100%, and lower production rate. Therefore, smaller diameter pipe is mostly a straight seam welded, large diameter spiral welded pipe is mostly used.


Production Control Measures for Thick Wall Spiral Steel Pipe
The production control of the thick-walled spiral steel pipe is to increase the plastic toughness of the steel pipe, improve the cleanliness of the molten steel, reduce the harmful inclusions, and improve the overall quality of the steel pipe. In the production process, a reasonable cooling system is adopted to avoid internal cracks and enhance the quality of steel pipes in many aspects.
SSAW steel pipe in the production process of reasonable control of the heating temperature, through the determination of the thermoplastic curve, select the best heating temperature. The billet heating should also pay attention to enough heat preservation time to reduce the deformation resistance and increase the toughness of the thick-walled spiral pipe plastic.
SSAW steel pipe production process requires more procedures, the final step is to reduce the roller speed, the roller speed is the key parameter of the perforation process, the roller rotation speed from low to high changes in the process, there is a layer of critical starting roller speed. When the rotation speed of the roller is low, the tube blank is easy to form a cavity; when the roller rotation speed is high, the tube blank and the structural spiral steel pipe easily form a delamination defect. In order to eliminate the delamination defects of the tube blank and the structural spiral steel tube, the rotation speed of the roll should be reduced to below the critical roll speed at which delamination begins.

Application:
The spiral welded pipe is mainly used in tap water engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation and urban construction. It is one of the twenty key products developed by China. For liquid transport use: water supply, drainage, sewage treatment works, mud transport, marine water transport. For gas transportation: gas, steam, liquefied petroleum gas. For structural use: as a pile driving pipe, as a bridge; piers, roads, building structures, marine piling pipe. Spiral welded pipes undergo stringent physicochemical tests before they are put into use. Spiral seam submerged arc welded pipe for pressure-bearing fluid transportation is mainly used for pipelines conveying petroleum and natural gas. The steel pipe has strong pressure bearing capacity and good plasticity, which is convenient for welding and processing and forming. In general, spiral submerged arc welded steel pipe for low pressure fluid transportation adopts double-sided automatic Submerged-arc welded or single-sided welding method for submerged-arc welded steel pipes used for the transport of low pressure fluids such as water, gas, air and steam.

For gas transportation: gas, steam, liquefied petroleum gas. For structural use: as a pile driving pipe, as a bridge; piers, roads, building structures, marine piling pipe. Spiral tube with strong pressure bearing capacity, good plasticity, easy for welding and processing and molding; general low pressure fluid conveying spiral steel pipe, using double-sided automatic submerged arc welding or single-sided welding method for the general low pressure of water, gas, air and steam submerged-arc welded steel pipe, straight seam steel pipe for fluid transport. Nowadays, the commonly used standards for large-diameter spiral steel pipes are generally divided into (partial standard, also known as spiral pipe for ordinary fluid transmission pipelines), national standard, also called oil and gas industry transmission steel pipe. Technical condition: Grade A steel pipe (up to now demanding steel pipe )) (American Petroleum Institute, also known as pipeline steel pipe; which is divided into two levels) large-caliber coated steel pipe is made by coating plastic on the basis of large-diameter spiral welded pipe and high-frequency welded pipe, if the diameter of the steel pipe reaches 1200mm, According to different needs can be coated with PVC (polyvinyl chloride), polyethylene (PE), epoxy resin and other various properties of the plastic coating, good adhesion, corrosion resistance, resistant to strong acids, alkalis and other Chemical corrosion, non-toxic, non-corrosive, wear-resistant, impact-resistant, strong penetration resistance, smooth surface of the pipeline, no adhesion of any substance, can reduce the resistance during transportation, increase the flow rate and transmission efficiency, and reduce the transmission pressure loss. There is no solvent in the coating, no leakage of substances, so it will not contaminate the transported media, so as to ensure the purity and sanitation of the fluid. It can be used alternately in the range of -40°C to +80°C, without aging, because it does not crack, it can be used in harsh environments such as cold areas. Large diameter coated steel pipes are widely used in tap water, natural gas, petroleum, chemical, pharmaceutical, telecommunications, electric power, marine and other engineering fields.


Meaning of SSAW Pipe
Spiral submerged arc welding(SSAW) is its forward direction and forming tube centerline hose reel molding angle (adjustable), side molding edge welding and weld them into a spiral.
(Spirally Submerged Arc Welding pipes) SSAW pipes: SSAW pipes are produced by spiral (helicoidal) welding of steel coil and have a cost advantage over LSAW pipes, as the process uses coils rather than steel plates. As such, in applications where spiral-weld is acceptable, SSAW pipes may be preferred over LSAW pipes. Both LSAW pipes and SSAW pipes compete against ERW pipes and seamless pipes in the diameter ranges of 16”-24”. SSAW pipes are mainly used in petroleum and natural gas industry to transport flammable and non-flammable liquid and steel construction.

SSAW Pipe, it is made by winding a low carbon carbon structural steel or low alloy structural steel strip into a blank according to a certain helix angle (called forming angle), and then welding it together. It can be used in a narrower way. Strip production of large diameter steel pipes. Its specifications are expressed in terms of outer diameter and wall thickness. The welded pipe should ensure that the hydrostatic test, the tensile strength and the cold bending performance of the weld be in compliance with the regulations.

Advantages of ssaw steel pipe:
(1) The use of steel strips of the same width enables the production of steel pipes of different diameters, in particular the production of large-diameter steel pipes with narrow strip steel.
(2) Under the same pressure conditions, the spiral welds are subjected to a smaller stress than the straight seams, which is 75% to 90% of the straight seam welded pipes, and can therefore withstand greater pressures. Compared with the straight welded pipe with the same outer diameter, under the same pressure, the wall thickness can be reduced by 10% to 25%.
(3) Accurate size, general diameter tolerance is not more than 0.12%, deflection is less than 1/2000, ellipticity is less than 1%, and sizing and straightening processes are generally omitted.
(4) It can be continuously produced. In theory, it can produce infinitely long steel pipes, and the loss of cutting and cutting tails is small, which can increase the metal utilization rate by 6% to 8%.
(5) Compared with the straight seam welded pipe, its operation is flexible and the adjustment of the replacement type is convenient.
(6) The equipment is light and the initial investment is small. It can be made into a trailer-type flow unit and the welded pipe can be produced directly at the construction site where the pipeline is laid.
(7) It is easy to realize mechanization and automation.
The disadvantage of ssaw steel pipe: due to the use of rolled steel as raw material, there is a certain crescent of the crescent, and the welding point is in the edge zone of the elastic strip, so it is difficult to align the welding torch and affect the welding quality. To this end, complex weld seam tracking and quality inspection equipment must be set up.

How to increase the stability of the ssaw steel pipe?
First, Small and medium-sized steel, wire rods, steel bars, medium-diameter steel pipes, steel wires and wire ropes, etc., can be stored in a well-ventilated shed, but must be lining up and down.
Second. Some small steel materials, thin steel plates, steel strips, silicon steel plates, small-caliber or thin-walled steel pipes, various cold-rolled and cold-drawn steel products, and expensive, easily corroded metal products may be stored in storage.
Third. The place or warehouse where spiral steel pipe products are to be kept should be located in a clean and unobstructed place, away from factories and mines that produce harmful gases or dust. Weeds and all debris should be removed from the site to keep the steel clean.
Fourth, Large-sized steel, steel rails, insult steel, large diameter steel pipes, forgings, etc. can be stacked in the open air.
Fifth, In the warehouse must not be stacked together with acid, alkali, salt, cement and other materials that are aggressive to steel. Different types of steel should be stacked separately to prevent confusion and prevent contact corrosion.

Flaw Lnspection of SSAW Steel Pipe
As a highly efficient special transportation means, pipeline transportation has played an increasingly important role in the fields of oil and gas transportation. Domestic large-diameter transportation pipelines are currently mainly constructed with ssaw steel pipe. In order to ensure the reliable operation of the transportation pipeline, the quality of the spiral steel pipe used must be strictly guaranteed. Therefore, it is necessary to perform non-destructive inspection on the weld before shipment to eliminate hidden dangers.
In the developed countries of Europe and the United States, people knew the non-destructive testing of steel pipes earlier, and invested a lot in the development and use of testing equipment. Compared with foreign countries, China’s testing equipment is lagging behind, and the detection of steel pipe welds is basically carried out using manual or semi-automatic equipment. Because inspection efficiency is very low, inspection methods can usually only be used to detect completely each steel pipe. Possible defects. In various international bidding activities, it is usually required that the steel pipe production enterprises participating in the bidding have relatively complete testing measures. Some enterprises have introduced some automatic testing equipment from abroad despite spending huge sums of money, but due to restrictions on domestic production and inspection supporting conditions However, its use effect is often unsatisfactory. As a result, many imported equipment is idle and a lot of money is wasted. The current situation has greatly limited the international competitiveness of domestic steel pipe manufacturers. Therefore, the non-destructive testing of steel pipe welds has always been an important problem that all companies can’t solve and needs to be solved urgently. It is urgent to develop an automatic weld inspection device suitable for the production conditions in China. This article will first introduce the overall composition of an automated ultrasonic flaw detection system for ssaw steel pipe weld seam inspection. The mechanical and electrical structure of the weld seam tracking mechanism, which is the heart of the inspection equipment, will then be introduced. The working process of the automatic flaw detection system will be described.

The Quality of SSAW Steel Pipe Depends on the Quality of the Weld
For ssaw steel pipe, we all know that the quality of the ssaw steel pipe is the most important thing for the quality of the whole spiral steel pipe, but the inspection of the geometric size of the spiral steel pipe can not be underestimated. So what tools do we use to measure the geometrical dimensions of spiral steel pipes? Here we give you a brief introduction:
1. Inspection of outer diameter and ellipticity of spiral steel pipe: caliper, vernier caliper and ring gauge, measuring the maximum and minimum points.
2. Check the thickness of the spiral steel pipe: Micrometer, ultrasonic thickness gauge, no less than eight points at both ends and record.
3. Spiral steel pipe end face angle and blunt edge inspection: square, card board.
4. Check the length of spiral steel: steel tape, artificial, automatic length measurement.
5. Spiral steel tube bending inspection: ruler, horizontal ruler (1m), feeler ruler, thin line measured per meter bending, full-length bending.
In the production of ssaw steel pipe, the relationship between the stability of the forming and the quality of the welding is very close, and only the quality of the forming is improved and the welding quality is fully guaranteed. Spiral steel pipe joint gap size and change in the welding, to ensure that the spiral steel pipe weld appearance good shape, a certain depth of penetration, it requires the steel plate gap to be uniform, at the same time, according to the different gap gap, Use different welding specifications. In the spiral steel pipe, due to the crooked bend and “s” bend of the steel strip, the unevenness of the forming gap is caused, which brings difficulties to the welding, causes the welding seam to be unstable in penetration, and also causes the weld seam to remain high. The change, the forming seam is loose, the weld penetration is deep, the remaining height is reduced; when the forming seam is tight, the weld penetration is small, the residual height is increased, so in the welding process, the solution to this problem is: forming seam When loose, reduce the welding specification and increase the welding specification when tightly forming the joint. However, the gap between the forming gaps is constantly changing. In the operation of manually adjusting the gaps of the forming gaps by the naked eye, the small changes cannot be accurately monitored. Therefore, the control cannot be realized. Only when the changes are manually adjusted to a certain degree. The effect of this is very clear on the degree of redness of the back surface of the spiral welded steel pipe. When the slot is loose, the red line is bright, causing serious arcing and even burning through; when the seam is tight, the red line is dark and the appearance of the spiral steel pipe weld appearance. For the uneven, uneven width, serious, the middle of the weld pit, so a lot of spiral steel pipe manufacturers use the automatic control of forming gap to maintain the stability of the forming gap. In the adjustment of the welding specification, the degree of redness of the back surface of the weld should be adjusted slowly within a small range. Otherwise, the depth of penetration of the inner weld may be too shallow or burnt, resulting in incomplete penetration or unstable appearance quality.

Difference between lsaw steel pipe and ssaw steel pipe
1, Difference between lsaw steel pipe and ssaw steel pipe in production process 
LSAW steel pipe is a longitudinally parallel steel pipe. Usually divided into metric welded steel pipe, welded thin-walled pipe, transformer cooling oil pipe and so on. The straight seam welded pipe has a simple production process, high production efficiency, low cost, and rapid development. SSAW steel pipe is a coiled steel pipe made from strip coils as the raw material, which is often warm extruded and welded by an automatic double wire double-sided submerged arc welding process.
The strength of the ssaw steel pipe is generally higher than that of the lsaw steel pipe. A narrower blank can be used to produce a larger diameter pipe, and a blank having a different diameter can be produced from a blank of the same width. During the forming process, the steel plate is uniformly deformed, the residual stress is small, and the surface is free of scratches. The processed spiral steel pipe has greater flexibility in the range of diameters and wall thicknesses, especially in the production of high-grade thick-walled pipes, especially small- and medium-caliber thick-walled pipes, which have unparalleled advantages over other technologies and can satisfy users. More requirements on the specifications of spiral steel pipe. The use of advanced double-sided submerged arc welding technology can achieve welding in the best position. It is not prone to defects such as misalignment, welding deviation and incomplete penetration, and it is easy to control the welding quality. However, compared with the straight seam pipe of the same length, the length of the weld seam increases by 30 to 100%, and the production speed is low.
2, Difference between lsaw steel pipe and ssaw steel pipe in security analysis
LSAW steel pipe is mainly subjected to residual stress caused by inhomogeneous cooling. Residual stress is the stress of internal self-phase equilibrium under no external force. Hot rolled section steel of various sections has such residual stress. The larger the section size of general steel, the greater the residual stress is. Although the residual stress is self-balanced, it still has certain influence on the performance of steel components under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance; after welding, The non-metallic inclusions inside the straight seam steel pipe are pressed into thin slices, and the delamination phenomenon occurs. The delamination weakens the performance of the straight seam steel pipe in the thickness direction, and there is a possibility of interlayer tearing when the weld seam shrinks. The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than the strain caused by the load. In addition, the lsaw steel pipe will inevitably have many T-welds, so the probability of welding defects is also greatly improved. Moreover, the welding residual stress at the T-weld is large, and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracking.
SSAW steel pipe with spiral weld distribution, long weld, especially in the dynamic conditions of welding, the weld is too late to leave the molding point of cooling, easy to produce welding hot cracks. The direction of the crack is parallel to the weld and is at a certain angle to the axis of the steel tube, typically between 30-70°. This angle is just in line with the shear failure angle, so its bending, tensile, compressive and torsional resistance is far inferior to the LSAW pipe. At the same time, due to the limitation of the welding position, the resulting saddle shape and ridge-shaped welding seam influence Beautiful. In addition, during the construction process, the intersecting line welds at the spiral welded parent pipe joints split the spiral joints and generate larger welding stress, which greatly weakens the safety performance of the components. Therefore, the non-destructive testing of the spiral welded pipe joints should be strengthened. Ensure welding quality, otherwise spiral submerged arc welded pipe should not be used in important steel structure occasions.
3, Difference between lsaw steel pipe and ssaw steel pipe in the scope of application
LSAW pipe adopts double-side submerged arc welding process. Welding under static conditions, the quality of the weld is high, the weld is short, and the probability of defects is very small. The steel pipe expands through full-length, has a good pipe shape, and is precise in size. The steel pipe has a wide wall thickness range and a wide range of pipe diameters. It is suitable for supporting columns, ultra-large span building structures, such as buildings, bridges, dams, and offshore platforms, as well as wind-resistant and earthquake-resistant structures. Pole mast structure. Spiral steel pipe is a kind of steel commonly used in industry, construction and other industries. Mainly used in tap water projects, petrochemical industry, chemical industry, power industry, agricultural irrigation, urban construction.
In summary, we can see that the two different types of welded seam pipes have their own characteristics and have different advantages according to different applications.

Comparison for spiral steel pipe and seamless steel pipe

Seamless steel pipe is a kind of hollow section, and the peripheral no joint of strip steel. Seamless steel pipeis no seam, hot or cold drawing process molding. Characteristic is confined good.
2017122192187110568 - What is a spiral steel pipe?
Spiral steel pipe features: straight seam welding pipe production process is simple, high production efficiency, low cost. the strength of the spiral welded pipe is usually better than straight seam welding pipe is high, which can use a narrow billet production of larger diameter welded pipe, still can use the same width of the billet production pipe diameter different welded pipe. 
But with the same length straight seam pipe, compared to weld length increases 30 ~ 100%, and the production speed is low. Therefore, a small-bore pipe welding mostly adopts the straight seam welding, large diameter welded pipe is mostly using spiral welded.

Spiral steel pipe‘s type is made by strip, seamless steel pipe type is made by round steel, difference is very big, production process different: 

Spiral steel pipe is to use strip steel welding, can see the weld;

Seamless steel pipe is made with round steel punched, Spiral steel pipe wall thickness difference under very big, and Seamless steel pipe small pipe under basic no difference, the difference for bassoon and will not many.

Material:
Q235A, Q235B, 10#, 20#, Q345(16Mn), L245(B), L290(X42), L320(X46), L360(X52), L390X56), L415(X60), L450(X65), L485(X70), L555(X80), L290NB/MB(X42N/M), L360NB/MB(X52N/M), L390NB/MB(X56N/M), 415NB/MB(X60N/M), L450MB(X65), L485MB(X70), L555MB(X80)
As a spiral pipe manufacturer, we have the most advanced double-sided submerged arc welding steel tube production lines and can produce the SSAW pipes with diameter θ 219mm-θ2200mm and wall thickness from 6mm to 25mm. The double-sided submerged arc welding processing boasts not only in high deposition rate, but also with deep penetration ability, good quality and appearance of welding line and high density.
All these can meet your requirements of welding line. And the various production line make us the leading supplier of fire fighting sprinkler system in China, and our fire sprinkler pipe is also appreciated by lots of customers among the market.

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

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@pipelinedubai.com

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References:

  • https://www.yaang.com

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