Large diameter spiral steel pipe Cangzhou Haile Steel Pipe Co., Ltd

  Large diameter spiral steel pipe large diameter spiral steel pipe is a general term, generally refers to the spiral steel pipe with a diameter greater than 1 meter
Spiral steel pipe is made by bending steel strip and then welding

sketch
Large diameter spiral steel pipe is a general term, which generally refers to the spiral steel pipe with a diameter greater than 1 meter
Spiral steel pipe is made by bending steel strip and then welding
Water pressure, bending, flattening and other tests shall be carried out for steel pipes
There are certain requirements for surface quality
Generally, the delivery length is 12M, and it is often required to deliver in fixed length
The specification of spiral steel pipe is expressed in nominal diameter (mm)
The nominal diameter is different from the actual diameter
According to the specified wall thickness, there are two kinds of ordinary steel pipe and thickened steel pipe

Materials: Q235A, Q235B Q23b,0Cr13、1Cr17、00Cr19Ni11、1Cr18Ni9、0Cr18Ni11Nb
　Q345 L245 L290 X42 X46 X70 X80
purpose
Spiral steel 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 20 key products developed in China
For liquid transmission: water supply and drainage
For gas transmission: coal gas, steam, liquefied petroleum gas
For structure: as pile driving pipe and bridge; Pipes for wharf, road, building structure, etc

Production process
Spiral steel pipe is a kind of spiral seam steel pipe, which is formed by warm extrusion and welded by automatic double wire double-sided submerged arc welding The main production processes are as follows:
(1) Raw materials, i
e
strip steel coil, welding wire and flux
Before being put into operation, it must undergo strict physical and chemical tests

(2) The butt joint between the head and tail of the strip steel shall adopt single wire or double wire submerged arc welding, and the automatic submerged arc welding shall be adopted for repair welding after the rolled steel pipe

(3) Before forming, the strip steel is leveled, trimmed, planed, cleaned, transported and pre bent

(4) The electric contact pressure gauge is used to control the pressure of the pressing oil cylinder on both sides of the conveyor to ensure the smooth transportation of the strip steel

(5) Adopt external control or internal control roll forming

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

(7) Both internal and external welding adopt Lincoln Electric welding machine to conduct single wire or double wire submerged arc welding, so as to obtain stable welding specifications

(8) All welded welds are inspected by online continuous ultrasonic automatic flaw detector, ensuring 100% coverage of nondestructive testing for spiral welds
If there is any defect, it will automatically alarm and spray the mark, and the production workers will adjust the process parameters at any time to eliminate the defect in time

(9) The steel pipe is cut into single pieces by air plasma cutting machine

(10) After cutting a single steel pipe, the first three steel pipes of each batch shall be subject to a strict first inspection system to check the mechanical properties, chemical composition, fusion condition of the weld, the surface quality of the steel pipe and the non-destructive flaw detection to ensure that the pipe manufacturing process is qualified before it can be officially put into production

(11) The parts with continuous acoustic flaw detection marks on the weld shall be rechecked by manual ultrasonic and X-ray
If there is any defect, it shall be repaired and then subjected to NDT again until it is confirmed that the defect has been eliminated

(12) The butt weld of strip steel and the pipe where the T-joint intersects with the spiral weld have all been inspected by X-ray television or film

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

(14) The pipe end is machined so that the perpendicularity, slope angle and blunt edge of the end face can be accurately controlled

Submerged arc welding process
The spiral steel pipe is welded by submerged arc welding; Forming process, forward swing intermittent production; Unit speed, 0
5--3m/min; Welding speed, 0
5--3m/min
The unit is composed of uncoiler, straightening machine, centering device, hydraulic shear, milling welding machine, disc shear, edge milling machine, plate surface cleaning equipment, delivery machine, plate edge pre bending equipment, forming machine, internal welding, external welding, flash, pulling out, slag dumping, repair welding, flat head chamfering, hydraulic inspection, finished product inspection, and oil removal collection
The whole process of submerged arc welding of spiral steel pipe is as follows:
Principle of spiral steel pipe submerged arc welding: submerged arc welding uses arc heat energy for welding
Different from manual electrode arc welding, the welding wire of submerged arc welding is exposed without coating
The flux of submerged arc welding is indeed pre laid at the place to be welded
The submerged arc welding wire extends into the flux, and the arc burns under the flux
The welding wire contacts with the workpiece
After pressing the start button, at the moment when the welding wire and workpiece are energized, the welding wire is pulled back, the arc is ignited, the welding trolley moves forward, and the welding wire is continuously transported downward to maintain the arc burning under the flux layer and form a welding pool under the arc
Around the arc, the flux melts to form a cavity,
The cavity and the molten pool advance continuously, while the metal behind the molten pool solidifies to form a continuous weld
This process is carried out under the flux, so we can't see it with the naked eye
It can be seen by means of X-ray photography

Because the spiral steel pipe adopts the welding technology of submerged arc automatic welding, the production efficiency is high; The auxiliary time for production is less, which saves the time for electrode replacement; The welding conditions are clean without splash, saving the cleaning time; High weld quality
It also provides the necessary conditions for the delivery of spiral steel pipe factory, so that the production time of a large number of spiral steel pipes can be guaranteed
Therefore, it is still widely used

Spiral seam submerged arc welded steel pipe is a spiral seam steel pipe made by bending the strip steel according to the spiral shape and welding the inner seam and outer seam with automatic submerged arc welding
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, steel pipes of various diameters can be produced with the same width of strip steel;
2) Because it is formed by continuous bending, the fixed length of steel pipe is not limited;
3) The weld is uniformly distributed on the whole circumference of the steel pipe, so the steel pipe has high dimensional accuracy and high strength;
4) The equipment is cheap and easy to change the size
It is suitable for the production of small batch and multi variety steel pipes

Weld type
Weld types of large diameter spiral steel pipes
Butt weld: refers to the circumferential weld formed by connecting two steel pipes together

Butt welding seam of steel strip: it refers to the seam connecting the head and tail of steel plate or steel strip on the spiral seam steel pipe

Tack weld: refers to the weld used to fix the butt edge before the final welding

Requirements for weld surface of large diameter spiral steel pipe
The weld appearance of large-diameter spiral steel pipe shall be uniform and regular, and the transition shall be gentle
The weld surface shall be free of defects such as arc breaking, burn through, crack, scar, folding, arc pit, etc

Causes of misalignment
Causes of misalignment of large diameter spiral steel pipe:
In the production of large-diameter spiral steel pipe, misalignment often occurs, which is affected by many factors
In production practice, the steel pipe is often degraded due to the out of tolerance of the wrong side
Therefore, it is necessary to analyze the causes and preventive measures of misalignment of large-diameter spiral steel pipe

1
The sickle bending of steel strip is the most important factor to cause the steel pipe misalignment
In the forming of spiral welded pipe, the sickle bend of steel strip will constantly change the forming angle, resulting in the change of weld gap, resulting in seam opening, staggering and even overlap
The quality of steel pipe is seriously affected
Therefore, observing the sickle bending of steel strip after uncoiling, controlling the vertical roll so that the disc shear can cut off part of the sickle bending, and continuously controlling and correcting the forming angle are effective ways to reduce the edge misalignment of steel strip sickle bending in the production process

2
Due to the poor shape and dimensional accuracy of the head and tail of the non trimming steel strip, it is easy to cause hard bending of the steel strip and wrong edges during butt joint

3
When the weld reinforcement of butt welding of steel strip head and tail is large, it is easy to cause large misalignment if it is not handled properly during overmolding

4
The poor condition of the steel strip edge is another important reason for the misalignment
Steel grade representation
Steel grade representation of large diameter spiral steel pipe:
Carbon structural steel
① It consists of q+ number + quality grade symbol + deoxidation method symbol
Its steel grade is marked with “ Q”, Represents the yield point of steel, and the following figures represent the yield point value, in MPa
For example, Q235 represents carbon structural steel with a yield point (σ s) of 235 MPa

② If necessary, symbols indicating quality grade and deoxidation method can be marked after the steel grade
The quality grade symbols are a, B, C and D respectively
Deoxidation method symbol f refers to rimmed steel, B refers to semi stabilized steel, Z refers to stabilized steel, TZ refers to special stabilized steel, and the symbol may not be marked for stabilized steel, that is, both ZT and TZ may not be marked
For example, q235-af represents class a rimmed steel

③ Carbon steel for special purposes, such as bridge steel, marine steel, etc
, basically adopts the representation of carbon structural steel, but the letter indicating the purpose is added at the end of the steel grade

High quality carbon structural steel
① The two digits at the beginning of the steel grade indicate the carbon content of the steel, which is expressed by a few tenths of the uniform carbon content
For example, for steel with a uniform carbon content of 0
45%, the steel grade is “ 45”， It is not a sequence number, so it cannot be read as 45 steel

② High quality carbon structural steel with high manganese content shall be marked with manganese, such as 50Mn
③ Rimmed steel, semi stabilized steel and high-quality carbon structural steel for special purposes shall be specially marked at the end of the steel grade
For example, the steel grade of semi stabilized steel with uniform carbon content of 0
1% is 10B

Carbon tool steel
① Steel grade is prefixed with “ T”， Avoid mixing with other steels

② The number in the steel grade indicates the carbon content, which is expressed as a few thousandths of the uniform carbon content
For example “ T8” Indicates that the uniform carbon content is 0
8%

③ If the manganese content is high, mark “ at the end of the steel grade; Mn”， For example “ T8Mn”。
④ The phosphorus and sulfur content of high-quality carbon tool steel is lower than that of general high-quality carbon tool steel, and the letter “ A”， To show the difference, for example “ T8MnA”。
development direction
The main development direction of spiral steel pipe plant is:
(1) Design and produce steel pipes with new structure, such as double-layer spiral welded steel pipes, that is, double-layer pipes are welded with strip steel with a thickness of half of the pipe wall, which not only has higher strength than single-layer pipes with the same thickness, but also will not show brittle damage;
(2) Develop new steel grades, improve the technical level of smelting process, widely adopt controlled rolling and post rolling waste heat treatment process, so as to continuously improve the strength, toughness and welding function of pipe body;
(3) Developing coated pipes vigorously, such as coating the inner wall of the pipe with anti-corrosion coating, can not only prolong the service life, but also improve the smoothness of the inner wall, reduce fluid friction resistance, reduce wax and dirt, reduce pigging times and reduce maintenance costs;
(4) Produce large diameter thick wall pipe to improve pressure resistance

Steel tube bearing algorithm
1： Calculation method for calculating the bearing pressure based on knowing the outer diameter specification and wall thickness of seamless steel pipe (the tensile strength of different materials of steel pipe is different)
Pressure = (wall thickness *2* tensile strength of steel pipe material) / (outer diameter * coefficient)
2： Calculation method of wall thickness based on knowing the outer diameter of seamless steel pipe and bearing pressure:
Wall thickness = (pressure * outer diameter * coefficient) / (2* tensile strength of steel pipe material)
3： Expression method of steel pipe pressure coefficient:
Pressure p< 7MPa coefficient s=8
7< Steel pipe pressure p< 17
5 coefficient s=6
Pressure p> 17
5 coefficient s=4 [2]