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Spiral welded pipe

Hits:Updated:2018-08-14 10:08:52【Print】

The low carbon carbon structural steel or the low alloy structural steel strip is rolled into a tube blank at a certain angle of the helix (called a forming angle), and then the pipe joint is welded, which can be produced by using a narrow strip steel. Large diameter steel pipe. Spiral welded pipe is mainly used for oil and natural gas transmission pipelines, and its specifications are expressed by outer diameter * wall thickness. Spiral welded pipes are single-sided welded and double-sided welded. The welded pipe shall ensure that the hydraulic test and the tensile strength and cold bending performance of the weld are in compliance with the regulations.
Spiral welded pipe production and spiral welded pipe technical characteristics
1, production plan
Rent land in Chengdu, establish a factory, and relocate equipment to the Chengdu plant.
2, equipment
Main unit: BYAND-2000 pipe-making unit manufactured by WILSON BYAND Company of the United Kingdom. The unit is divided into sections and has a total weight of about 130 tons. It can be divided into four main parts for single transportation, which is suitable for laying equipment on site. On-site production, on-site supply of steel pipes. The overall performance parameters of the unit are as follows:
Steel pipe specifications Minimum Φ400×5.0mm, maximum Φ3048×25.4mm
Pipe length is generally 6 ~ 30m, up to 80m
Raw material plate width, minimum 700mm, maximum 2000mm
Coil weight up to 40 tons
Material grade up to API 5L×65
Internal and external timely butt welding machine LINCOLN DC-1500
Main drive final drive DAVID BROWN RADICON
Ion-type cutting machine LINCOLN PRO-CUT 125
Hydraulic system VICKERS, DENISON
Electronic control system SIEMENS, ABB
3 Process
Unwinding - Rolling - Leveling - Butt welding - Milling edge - Forming - Internal welding - External welding - Pipe cutting - Breaking - Subsequent welding - Hydraulic test
4. Inspection process
Raw Material Inspection - Leveling Inspection - Butt Welding Inspection - Forming Inspection - Internal Welding Inspection - External Welding Inspection - Pipe Cutting Inspection - Ultrasonic Inspection - Groove Inspection - Dimensional Inspection - X-ray Inspection - Hydraulic test - final inspection
5. Anti-corrosion
· Domestic anti-corrosion materials generally use cement mortar, and some use non-toxic epoxy paint (thickness 0.4mm).
· Domestic and international anti-corrosion coating EDM test voltage is generally 3000 volts, the maximum is not more than 5000 volts, and the technical content is high 10 kV.
To achieve better anti-corrosion effect, you need to pay attention to two points:
· Strict sanding work procedures to ensure the quality of derusting, and the spraying of the inner and outer primers within one hour, which is the basis for ensuring the quality of anti-corrosion.
· When formulating the anti-corrosion process, it is required to specially require the glass cloth to first impregnate the epoxy coal bitumen paint, semi-mechanically tumble, and operate the glass cloth by the manual roller to ensure the uniformity and fineness of the outer coating.
·The inner and outer anti-corrosion pipes are placed in the open storage yard for 4 months, the inner coating has no yellow pitting, and the external anti-corrosion layer electric discharge test can still reach the requirement of 10 kV.
6. Comparison of technical characteristics between spiral welded pipe and straight welded pipe
Make a simple comparison between the technical characteristics of spiral welded pipe and straight welded pipe:
· Metallurgical properties of materials
Straight seam submerged arc welded pipes are produced from steel plates, and spiral welded pipes are produced from hot rolled coils. The hot rolling strip unit rolling process has a series of advantages, and has the metallurgical process capability for producing high quality pipeline steel. For example, a water cooling system is installed on the output gantry to accelerate cooling, which allows the use of low alloying compositions to achieve special strength levels and low temperature toughness, thereby improving the weldability of the steel. But this system is basically not available in steel plate production plants. The alloy content (carbon equivalent) of the coiled sheet is often lower than that of similar grades, which also improves the weldability of the spiral welded pipe.
It should be further noted that since the coil rolling direction of the spiral welded pipe is not the direction of the vertical steel pipe axis (the pinching depends on the helix angle of the steel pipe), the rolling direction of the straight steel pipe is perpendicular to the axial direction of the steel pipe, and thus, the spiral The crack resistance of the welded pipe material is superior to that of the straight seam steel pipe.
·Welding process
From the welding process, the welding method of spiral welded pipe and straight seam steel pipe is the same, but the straight seam welded pipe will inevitably have many T-weld joints, so the probability of welding defects is greatly improved, and the welding residual at the T-weld joint The stress is large, and the weld metal tends to be in a three-direction stress state, increasing the possibility of cracking.
Moreover, according to the submerged arc welding process regulations, each weld should have an arc starting point and an arc extinction point, but each straight seam welded pipe cannot meet this condition when welding the circumferential joint, and thus there may be More welding defects.
·Strength characteristics
When the tube is subjected to internal pressure, it usually produces two main stresses on the pipe wall, namely radial stress δY and axial stress δX. The synthetic stress at the weld is δ=δY(l/4sin2α+cos2α)1/2, where α is the helix angle of the spiral welded pipe weld.
The spiral angle of the spiral welded pipe weld is generally 50-75 degrees, so the synthetic stress at the spiral weld is 60-85% of the main stress of the straight welded pipe. Under the same working pressure, the thickness of the spiral welded pipe of the same pipe diameter can be reduced compared with the straight welded pipe.
According to the above characteristics, we can know:
When the A spiral welded pipe is blasted, since the normal stress and the synthetic stress of the welded joint are relatively small, the blasting hole generally does not originate from the spiral welded joint, and its safety is higher than that of the straight welded pipe.
B. When there is a defect parallel to the spiral weld, since the screw weld is less stressed, the risk of expansion is not as great as that of the straight weld.
C. Since the radial stress is the maximum stress present on the steel pipe, the weld is subjected to the maximum load in the direction of the vertical stress. That is, the straight seam is subjected to the largest load, and the hoop weld is subjected to the least load, and the spiral seam is between the two.
·Static pressure burst strength
According to the relevant comparison test, it is verified that the yield pressure of the spiral welded pipe and the straight welded pipe is basically consistent with the measured value and theoretical value of the bursting pressure, and the deviation is close. However, whether it is yield pressure or burst pressure, the spiral welded pipe is lower than the straight welded pipe. The blasting test also showed that the circumferential deformation rate of the burrow of the spiral welded pipe was significantly larger than that of the straight welded pipe. It is confirmed that the plastic deformation ability of the spiral welded pipe is better than that of the straight welded pipe. The blasting hole is generally limited to one pitch, which is caused by the strong restraining effect of the spiral weld on the expansion of the crack.
·Toughness and fatigue strength
The trend of pipeline development is large diameter and high strength. As the diameter of the steel pipe increases and the steel grade used increases, the tendency of the ductile fracture to expand and expand is greater. According to tests conducted by relevant research institutions in the United States, although the spiral welded pipe and the straight welded pipe are of the same grade, the spiral welded pipe has high impact toughness.
Due to the change of the transmission line, the steel pipe is subjected to random alternating load during the actual operation. Understanding the low cycle fatigue strength of steel pipes is of great significance for judging the service life of pipelines.
According to the measurement results, the fatigue strength of the spiral welded pipe is the same as that of the seamless pipe and the electric resistance welded pipe. The test data is distributed in the same zone as the seamless pipe and the resistance pipe, and is higher than the general buried arc straight seam welded pipe.
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