The difference between spiral submerged arc welded steel pipe and straight seam steel pipe

The difference between spiral submerged arc welded steel pipe and straight seam steel pipe

2019-07-27 10:48:49 87

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 Seam steel pipe. Welded steel pipes are divided into straight welded pipes and spiral welded pipes in the form of welds.


What is a spiral submerged arc welded steel pipe?

Spiral-slot submerged arc welded steel pipe is formed by spiral bending of hot-rolled strip steel, and spiral seam steel pipe (also called spiral welded pipe and spiral pipe spiral steel pipe) is formed by automatic welding of submerged arc for inner and outer joints. It can be widely used in the production of large diameter steel pipes for the following reasons:

1) As long as the forming angle is changed, it is possible to produce steel pipes of various calibers with strips of the same width;

2) Because the continuous bending is formed, the length of the steel pipe is not limited;

3) The weld spiral is evenly distributed on the circumference of the whole steel pipe, so the steel pipe has high dimensional accuracy and high strength;

4) It is easy to change the size and is suitable for the production of small batch and multi-type steel pipes.


Since the defect is parallel to the weld, the defect of the weld is a diagonal defect for the spiral pipe. In the course of use, the principal stress direction of the steel pipe, that is, the equivalent defect length in the axial direction of the steel pipe is smaller than that of the straight pipe; secondly, since the pipeline steel is a rolled steel plate, the impact toughness has a large anisotropy.

The CVN value in the rolling direction can be three times higher than the CVN value perpendicular to the rolling direction. The main stress of the straight seam pipe is exactly perpendicular to the direction of the lowest impact resistance of the pipe, while the spiral pipe staggers the direction of the lowest impact resistance of the pipe, which turns the disadvantage of the length of the spiral pipe weld into an advantage.


Standard for spiral submerged arc welded pipe:

Usually welded pipes are used for the transportation of normally lower pressure fluids such as water, gas, air, oil and heating steam.

Ordinary carbon steel wire bushings (GB3640-88) are steel pipes used to protect electric wires in electrical installations such as industrial and civil buildings and installation machinery.

Straight seam welded pipe (YB242-63) is a steel pipe whose weld is parallel to the longitudinal direction of the steel pipe. Usually divided into metric electric welded pipe, welded thin-walled pipe, transformer cooling oil pipe and so on.

Spiral-slot submerged arc welded pipe (SY5036-83) for pressurized fluid conveying is a hot-rolled steel strip coil for tube blank, which is often spiral-formed by a double-sided submerged arc welding method, and is used for spiral fluid steel pipe for pressure fluid transportation. . The steel pipe has strong pressure bearing capacity and good welding performance. It is safe and reliable after various strict scientific tests and tests. The steel pipe has a large caliber, high conveying efficiency, and can save investment in laying pipelines. It is mainly used to transport oil and natural gas pipelines.

Spiral seam high-frequency welded pipe (SY5038-83) for pressurized fluid conveying is a hot-rolled steel strip coil for tube blank, which is often spiral-formed by high-frequency lap welding and used for spiral conveying of pressurized fluid. High-frequency welded steel pipe. The steel pipe has strong pressure bearing capacity and good plasticity, which is convenient for welding and processing. After various strict and scientific inspections and tests, the use is safe and reliable, the steel pipe has large caliber, high conveying efficiency, and can save investment in laying pipelines. It is mainly used for laying pipelines for transporting oil and natural gas.


Production process of spiral submerged arc welded steel pipe

Spiral steel pipe is a spiral seam steel pipe which is made of steel coiled coil as raw material, which is often heated and extruded, and welded by automatic double wire double-sided submerged arc welding process.

(1) Raw materials are strip coils, welding wire, flux. Strict physical and chemical testing is required before input.

(2) The steel head and tail are butt jointed, and the single wire or double wire submerged arc welding is used, and the automatic submerged arc welding is used after the steel pipe is rolled.

(3) Before forming, the strip is leveled, trimmed, planed, surface cleaned and pre-bent.

(4) The electric contact pressure gauge is used to control the pressure of the cylinder on both sides of the conveyor to ensure the smooth conveying of the strip.

(5) Adopt external control or internal control roll molding.

(6) The weld gap control device is used to ensure that the weld gap meets the welding requirements, and the pipe diameter, the amount of misalignment and the weld gap are strictly controlled.

(7) Both internal and external welding are performed by single-wire or double-wire submerged arc welding using a Lincoln welding machine in the United States to obtain stable welding specifications.

(8) The welded seams are all inspected by online continuous ultrasonic automatic injury inspection to ensure the non-destructive testing coverage of 100% spiral welds. If there is a defect, the alarm is automatically alarmed and sprayed, and the production worker adjusts the process parameters at any time to eliminate defects in time.

(9) The steel pipe is cut into individual pieces by an air plasma cutting machine.

(10) After cutting into a single steel pipe, each batch of steel pipe shall undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion condition, surface quality of the steel pipe and non-destructive testing to ensure the pipe making process. After that, it can be officially put into production.

(11) The part of the weld with continuous acoustic flaw detection mark, after manual ultrasonic and X-ray review, if it is defective, after repair, it will pass the non-destructive test again until it is confirmed that the defect has been eliminated.

(12) The tube of the butt weld of the strip and the joint of the butt joint intersecting the spiral weld are all inspected by X-ray television or film.

(13) Each steel pipe is subjected to hydrostatic pressure test and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. Test parameters are automatically printed and recorded.

(14) The pipe end is machined to make the end face verticality, groove angle and blunt edge accurately controlled.


What is a straight seam steel pipe?

Straight seam steel pipe is a steel pipe whose weld is parallel to the longitudinal direction of the steel pipe. Usually divided into metric electric welded steel pipe, welded thin-walled pipe, transformer cooling oil pipe and so on. 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.


Generally welded pipes are used to deliver low pressure fluids. Made of Q195, Q215A, Q235A steel, Q235B carbon. It can also be manufactured by easy welding of 0317 standard model 6012 and steel 755 mild steel. The steel pipe is subjected to experiments such as water pressure, bending and flattening, and has certain requirements on the surface quality. Usually, the delivery length is 4-10 m, and the fixed length (or double rule) is often required for delivery. The specifications of the welded pipe are expressed by the nominal diameter (mm or inch). The nominal diameter of the welded pipe is two kinds of ordinary steel pipe and thick steel pipe according to the specified wall thickness. The steel pipe is divided into two types according to the pipe end form: threaded and unthreaded.


The welding process of submerged arc welded straight seam steel pipe is submerged arc welding technology, which uses filler welding and particle protection flux submerged arc. The caliber of the production can reach 1500mm. LSAW is the abbreviation of submerged arc welded straight seam steel pipe. The production process of submerged arc welding straight seam steel pipe has JCOE forming technology and roll forming submerged arc welding technology. When the diameter is large, it may be rolled with two steel plates, which will form a double weld. Standard GB/T3091-2008 low-pressure fluid steel pipe production standard, GB/T9711.1-2 -1997 oil and gas steel pipe production and use standards can be implemented, and can also implement the US API 5L pipeline steel pipe implementation standard. Production materials: Q195A-Q345E; 245R; Q345QA-D; L245-L485; X42-X70. The pressure parameters are mainly 2ST/T, S is the yield strength, and T is the wall thickness. Submerged arc welding has been developed to have double-wire submerged arc welding and multi-wire submerged arc welding, and the efficiency is further improved.


Production process of straight seam steel pipe

According to the production process, straight seam steel pipes can be divided into high-frequency straight seam steel pipes and submerged arc welded straight seam steel pipes. Submerged arc welded straight seam steel pipes are further divided into UOE, RBE, JCOE steel pipes according to their different molding methods. The following describes the most common molding processes for high-frequency straight seam steel tubes and submerged arc welded straight seam steel tubes.


Submerged arc welding process

Panel inspection: After the steel plate used to manufacture the large-diameter submerged arc welded straight seam steel pipe enters the production line, the whole board ultrasonic inspection is first carried out;

Milling edge: double-sided milling of the two edges of the steel plate by the edge milling machine to achieve the required plate width, edge parallelism and groove shape;

Pre-bending edge: pre-bending the edge of the board with a pre-bending machine to make the edge of the board have the required curvature;

Molding: On the JCO molding machine, half of the pre-bent steel plate is first stepped and pressed into a "J" shape, and the other half of the steel plate is also bent and pressed into a "C" shape, and finally an opening is formed. O" shape

Pre-welding: joints of straight seam welded steel pipes after forming and continuous welding by gas shielded welding (MAG);

Internal welding: welding by longitudinal multi-wire submerged arc welding (up to four wires) on the inside of a straight seam steel pipe;

External welding: welding by longitudinal multi-wire submerged arc welding on the outside of straight seam submerged arc welded steel pipe;

Ultrasonic inspection I: 100% inspection of the inner and outer welds of straight seam welded steel pipes and the base metal on both sides of the weld;

X-ray inspection I: 100% X-ray industrial TV inspection of internal and external welds, using image processing system to ensure the sensitivity of flaw detection;

Expanding diameter: Expanding the full length of the submerged arc welded straight seam steel pipe to improve the dimensional accuracy of the steel pipe and improve the distribution of stress in the steel pipe;

Hydraulic test: On the hydraulic test machine, the steel pipe after the diameter expansion is tested one by one to ensure that the steel pipe meets the test pressure required by the standard. The machine has automatic recording and storage functions;

Chamfering: the steel pipe after passing the inspection is processed at the pipe end to achieve the required pipe end groove size;

Ultrasonic inspection II: Ultrasonic inspection is carried out again and again to check for defects that may occur after straightening and water pressure of straight seam welded steel pipes;

X-ray inspection II: X-ray industrial TV inspection and tube end weld filming of steel pipes after expansion and hydrostatic test;

Tube end magnetic particle inspection: Perform this inspection to find tube end defects;

Anti-corrosion and coating: The qualified steel pipe is preserved and coated according to user requirements.

The difference between spiral submerged arc welded steel pipe and straight seam 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 Seam 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, most of the smaller diameter welded pipes are straight seam welded, and the large diameter welded pipes are mostly spiral welded.


Generally, spiral submerged arc welded steel pipe (SY5037-2000) for low-pressure fluid transportation is made of hot-rolled steel strip as a tube blank, which is often spiral-formed by a double-sided automatic submerged arc welding or single-sided welding method for water. Submerged arc welded steel pipe for general low pressure fluid transportation such as gas, air and steam.

Generally, spiral high-frequency welded steel pipe (SY5039-83) for low-pressure fluid transportation is a hot-rolled steel strip coil for tube blank, which is often spiral-formed by high-frequency lap welding for high-pressure fluid conveying. Frequency welded steel pipe.


Spiral Welded Steel Pipe for Piles (SY5040-2000) is made of hot-rolled steel strip coils, often spiral-formed by double-sided submerged arc welding or high-frequency welding, used for civil engineering structures, wharfs and bridges. Steel pipes for foundation piles.


Welded steel pipe for low-pressure fluid transportation (GB/T3092-1993) is also called general welded pipe, commonly known as black pipe. 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 approximate value 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.


Galvanized welded steel pipe (GB/T3091-1993) for low-pressure fluid transportation is also called galvanized electric welded steel pipe, commonly known as white tube. It is a hot dip galvanizing (furnace welding or electric welding) steel pipe for transporting water, gas, air oil, heating steam, warm water and other general low pressure fluids or other purposes. 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 approximate value of the inner diameter. It is customary to use inches, such as 11/2.


Ordinary carbon steel wire bushings (GB3640-88) are steel pipes used to protect electric wires in electrical installations such as industrial and civil buildings and installation machinery.


Straight seam electric welded steel pipe (YB242-63) is a steel pipe whose weld is parallel to the longitudinal direction of the steel pipe. Usually divided into metric electric welded steel pipe, welded thin-walled pipe, transformer cooling oil pipe and so on.


Spiral submerged arc welded steel pipe (SY5036-83) for pressurized fluid conveying is a hot rolled steel strip coil for tube blank, which is often spirally formed by a double-sided submerged arc welding method and used for spiral conveying of pressurized fluid. Steel Pipe. The steel pipe has strong pressure bearing capacity and good welding performance. It is safe and reliable after various strict scientific tests and tests. The steel pipe has a large caliber, high conveying efficiency, and can save investment in laying pipelines. It is mainly used to transport oil and natural gas pipelines.


Spiral seam high-frequency welded steel pipe (SY5038-83) for pressurized fluid conveying is a spiral of hot-rolled steel strip, which is often spiral-formed by high-frequency lap welding and used for the conveying of pressurized fluid. High-frequency welded steel pipe. The steel pipe has strong pressure bearing capacity and good plasticity, which is convenient for welding and processing. After various strict and scientific inspections and tests, the use is safe and reliable, the steel pipe has large caliber, high conveying efficiency, and can save investment in laying pipelines. It is mainly used for laying pipelines for transporting oil and natural gas.


The strength of spiral welded pipe is generally higher than that of straight welded pipe. The main production process is submerged arc welding. Spiral steel pipe can produce welded pipe with different pipe diameter with blank of the same width, and can also produce welded pipe with larger diameter with narrower blank. However, compared with the straight pipe of the same length, the weld length is increased by 40% to 100%, and the production speed is low. Therefore, most of the smaller diameter welded pipes are straight seam welded, and the large diameter welded pipes are mostly spiral welded. In the production of large-diameter straight-slit spiral steel pipe in the industry, the T-welding technology will be used, that is, the short straight seam steel pipe will be butted to the length required to meet the engineering needs, and the probability of the T-weld straight seam steel pipe defect is greatly improved, and the T-shape The welding residual stress at the weld is large, and the weld metal tends to be in a three-direction stress state, increasing the possibility of cracking.

(1) The manufacturing process of spiral steel pipe determines its residual stress. According to foreign data, some even approach the yield limit. The submerged arc welded straight seam steel pipe adopts the pipe expansion process and the residual stress is close to zero.

(2) Spiral weld seam tracking and ultrasonic on-line detection and tracking are difficult. Therefore, the probability of weld blanking exceeds the standard is higher than that of straight seam submerged arc welded pipe.

(3) The amount of misalignment of spiral steel pipe welds is mostly 1.1-1.2mm. According to international practice, the amount of misalignment is less than 10% of the thickness. If the wall thickness of the pipe is small, the amount of misalignment is difficult to meet the demand, and the submerged arc welding is straight. Steel pipes do not have this problem.

(4) and straight seam submerged arc