On-site manufacturing process of large-diameter steel coil pipe

to use a large number of large-diameter unshaped steel coiled pipes. The steel coiled pipes used are difficult to manufacture and transport due to their large geometric dimensions and volume . The project adopts the production method of on-site steel pipe coiling, which solves the demand for large-diameter unshaped steel coil pipes in large-scale projects. The article summarizes the manufacturing process and quality control measures of on-site steel coil pipes, which can be used for reference by industry peers.
Key words steel coiled pipe; on-site coiling; non-standard size; automatic welding

1. Project Overview

A large-scale cross-sea project uses large-diameter unshaped steel coiled pipes. The diameter of the steel coiled pipes is ① 4200mm , the pipe wall thickness is 40mm , and the material is 16Mn steel . Each steel coiled pipe is 6-9m long and weighs 24-36t . The total length of steel coil pipes used in the project is about 5200m , and the total amount is more than 20,000 tons .
30m long steel coil pipes should be provided every day , and the daily production needs to be more than 120t to meet the requirements. Due to the large geometric size and volume of a single section of steel coiled pipe used in this project, it is difficult to manufacture, hoist, store and transport. At the same time, the project has high requirements on the technical quality of the steel coiled tubes used. The deviation of the vertical axis of the finished steel coiled tubes is not greater than 0.1% of the tube length , and shall not be greater than 10mm , and the deviation of the ellipticity of the steel coiled tubes is not greater than 5mm . To this end, the project is matched with the steel coil pipe project, and the production methods of on-site steel pipe coiling, computer-aided material lofting, numerical control cutting, program-controlled coiling, manual welding and gas shielded welding and other technological measures have been widely adopted, and high production has been obtained. It improves the efficiency, ensures the product quality, improves the working conditions of the welders and reduces the labor intensity of the workers.

1. Workshop construction and technical equipment

2.1 Site selection
According to the characteristics of the project, comprehensively considering the large volume of the single finished steel coil pipe, the difficulty of hoisting, storage and transportation, high technical quality requirements, and many factors such as project cost and cost, an open space is rented near the project to build a production workshop for Production, production, storage, hoisting and transportation, etc. The workshop should be equipped with a production line with a total width of 24 inches and a length of 150 inches . All production equipment should be fully equipped. Correspondingly separate the welding inspection area, sand blasting anti-corrosion area, and the area where steel coil pipes are parked for transportation. And there should be roads to facilitate transportation. The layout of the production line is shown in Figure 1 .

Table 1 Main tooling and equipment configuration
Equipment name	quantity
50x3200 three-roll plate rolling machine	1 unit
5.5x9 telescopic arm submerged arc automatic welding machine	2 parts
20t single girder gantry crane	2 parts
Transformer 500kVA	1 unit
50t crane	1 part
20t crane	1 part
10t forklift	2 parts
26kW welding machine	1 set
14kW welding machine	4 units
40kW air compressor	1 set
50kg/m rail	640m
Welding rod drying box	1 set
General control cabinet	1 set
electrical tools	20 units
5t hoist	2 units
Roller frame	4 pairs

According to the requirement of daily production of 120t steel coil pipe, the coiling equipment is selected from Jiangsu w11s -50 X 4000 large -scale universal plate rolling machine with top rollers . The welding workload of this project is high and the welding requirements are high . The total length of the weld seam is 20,000 . Coil pipe welding tasks. In order to be suitable for the application of the telescopic arm submerged arc automatic welding machine, the

800 coiled steel pipes , and the hoisting operation in the processing area is heavy. For this reason , two 20t gantry cranes are installed on the assembly line .
2.3 Manufacturing process of steel coil pipe crimping die
The steel plate crimping before coiling of the steel coil pipe is completed by using the crimping die and the plate rolling machine. According to the calculation based on the thickness of the plate and the strength of the steel, it is necessary to use a steel plate with a thickness of 80mm as the crimping die, and the existing rolling equipment It is impossible to complete the rolling of 80mm thick steel plate. After research, two pieces of 42mm thick steel plate are used to roll according to different radians to form an overlapping edge blanking formwork. After the upper and lower formwork rolls are completed, wires are laid on the overlapping formwork and round holes of ① 25 are drilled . The inner holes of the upper and lower steel plates are connected with round steel pins of ① 25 and then plugged. After plug welding, the protruding welding joint sand
Wheel grinding.

2.4 Manufacture of rotating turntable during transportation of steel coil pipe joints
After the longitudinal and circumferential welds of automatic submerged arc welding of steel coil pipes are completed, the length of each steel coil pipe is 6 ~ 9m , and the finished pipe joints are lifted from the automatic submerged arc welding platform for weld inspection and spraying. Sand anti-corrosion, after the completion of various processes, the steel coil pipe is transported to the waiting area of the finished product section, because the lifting position of the two gantry cranes is limited. The pipe joint must be turned 90 °. This project uses a self-made movable turntable to change the rotation direction of the pipe joints. When the gantry crane transports the pipe joints to the movable turntable, the turntable is rotated by manpower, and then separated to make the pipe joints roll to the designated place.

1. Steel Coiled Pipe Manufacturing Process

The process flow of steel coil pipe production is shown in Figure 1 . Mainly: No. material and steel plate blanking - plate connection (short plate butt joint) - edge pressing , roll forming - assembly , fixed welding - straight seam (longitudinal seam) welding (inner and outer ) - flaw detection ( X -ray, ultrasonic) Inspection — pipe and pipe group pairing , fixed welding — welding of circular seam ( inner and outer) —flaw detection ( X- ray , ultrasonic) inspection — sand blasting and anticorrosion — stacking area for transportation — hoisting and shipping. No. 3.1 material and steel plate blanking
Purchasing steel plates from national regular steel mills according to the requirements, after the arrival of the goods, they will be randomly inspected by on-site supervisors, and then sent to qualified units for re-inspection. The sampling samples of each batch shall not be less than 2% of the total amount of each batch . For the two steel plates, in addition to the inspection of surface appearance, chemical composition and mechanical properties, ultrasonic flaw detection is also required, and the steel plates that pass the inspection can be used.
The work content of blanking is: planking - nesting - scribing - cutting - marking - cleaning - inspection. In the calculation of the blanking size of the steel plate, the circumference length is calculated by the middle diameter of the steel pipe, and the obtained value is the theoretical value of the blanking steel plate size, and the rolling stretch and welding shrinkage of the steel plate are inevitable in the subsequent rolling and welding processes , for this reason, in order to obtain the steel coil pipe of the required size, the influence of factors such as steel plate rolling and welding shrinkage should be considered comprehensively when blanking, and an empirical value (coil extension and weld seam extension) should be subtracted from the theoretical size. Clearance) and groove cutting value, that is, the actual blanking cutting size of the steel plate surface is obtained. The welded joint of the steel coil pipe adopts the form of full penetration butt joint with open groove. Generally, when the thickness of the steel plate is less than 20mm , a single-sided groove can be used. This project uses a steel plate with a thickness of 40mm . Mouth preparation was carried out as shown in Figure 3 . For this reason, it can be determined that the blanking size of ① 4200 x 40 steel coil pipe in the circumferential direction is 4200 x 3.1416-3-2=13190 mm , where 3mm is the empirical value of rolling elongation and welding shrinkage, and 2mm is the groove Reserve gap value. 13 in the figure is the dimension related to the bevel, which should be taken into account when cutting the bevel. Semi-automatic flame cutting machine for blanking and bevel cutting .

Check the cut steel plate before formal coiling to see if it meets the specified size deviation. The specific items and deviation are as follows: the width and length allowable deviation ± 2m is called the diagonal relative difference allowable deviation is 3mm , and the corresponding side relative difference allowable deviation is 1.5mm , the depth of cratering on the cutting surface W lmm , the depth of the edge of the cutting surface W 1mm , the allowable deviation of the groove cutting angle is ± 1 ° , and finally check the cracks, slag addition, delamination (not allowed) and the slag on the cutting surface , burrs and tiny gaps, some are polished with an angle grinder.

1. Edge forming , roll forming

First use a press to preform the arc on the edge of the steel plate, that is, "edge pressing". Use a 20t door crane to hoist the plate that needs to be rolled to the plate rolling machine operation site, and make the rolling direction of the plate rolling machine and the steel plate consistent, start the lower roll to send the steel plate between the upper and lower rolls, and use the counter on the plate rolling machine The centering device centers the steel plate, and then starts the work rolls to press the two ends of the steel plate. During the crimping process, try to use a small amount of roll feed to repeat the coiling many times, so that the radians of both ends meet the requirements. During the edge pressing process, the length of the straight edge should be minimized, and the bottom roll of the plate rolling machine should be moved to cooperate with the upper roll to strictly control the arc of the end of the steel plate to prevent local concave or convex after rounding.
After the blanking is completed, arc curling is carried out, that is, the tile is rolled and formed. Adjust the lower (side) roll of the plate rolling machine back to its original position, and by adjusting the upper roll, also use a small amount of rolling roll to repeatedly press the middle part of the sheet. The rolling sequence is: roll the end of the board first, then roll the middle. During the rolling process, the sample plate with a chord length of 1.5m is continuously used to check the gap between it and the tile, and the parts that do not meet the requirements are re-rolled (that is, the arc is repaired); the plate should be checked every time it is rolled to the edge Whether the edge is parallel to the roll, strictly control the verticality of the center of the plate and the center of the roll of the roll machine to prevent distortion during the rolling process of the tile.
During the tile rolling process, attention should be paid to: ① The steel plate of the same thickness should be rolled as many times as possible to ensure the same elongation of the steel plate; ② It is strictly forbidden to hammer the steel plate when rolling the plate to prevent surface defects of the steel plate caused by hammering; ③ During the rolling process, the oxide scale, rust and other sundries on the steel plate should be checked and removed in time. If there are stretch marks and burrs on the base metal during the rolling process, the rolling should be stopped in time, and the polishing machine should be used to smooth it before Rolling; ④ After the tiles are rolled, the double lifting points should be hoisted evenly to prevent the tiles from being deformed due to unbalanced forces.

1. Group pair , fixed welding

The group pair is also called the group circle, which means that multiple arc tiles are assembled vertically on a special platform to form a circle. Each section ① 4200 x 40mm steel coil pipe is composed of 2 pieces of arc tiles, hoist the 2 pieces of arc tiles on the assembly platform, use tools such as pressing horses and jacks to tighten the tiles, and connect the steel pipes to the longitudinal seam Preliminary alignment, check whether the gap of the butt joint longitudinal seam meets the requirements, the assembly gap is 1 ~ 2mm , and the shrinkage determined during the welding procedure qualification test is controlled to ensure that the circumference of the steel pipe after welding reaches the allowable deviation required by the specification, and then use the Calibrated steel pan ruler, template, gap inspection ruler, misalignment inspection ruler and other tools to check the roundness of steel pipes after assembly (at least 4 pairs of diameters), the circumference of the nozzle at both ends, the arc at the longitudinal seam, and the plane of the nozzle Degree, longitudinal seam gap and longitudinal seam misalignment and adjusted to pass. After the steel pipe assembly is completed, the stiffening ring is assembled and welded on the spot. Before the stiffening ring is assembled, the welding position is marked on the steel pipe wall, the supporting plate is welded, and the stiffening ring is placed on the supporting plate. It should be vertical and close to the pipe wall, and the local gap should not be greater than 3mm . When splicing the stiffening ring, the joint gap should be <4mm . When assembling, the welding seam during splicing should be staggered. Flat fillet welding is adopted for the stiffening girth weld, and the pipe is turned over 180 ° after one side is welded, and the welding is continued after gouging, root cleaning and grinding.
3.4 Steel coil pipe welding
Steel coil pipe welding includes straight seam (longitudinal seam) welding and circular seam welding. The base material of the steel coil pipe is 16Mn low alloy steel, and the welding material is selected according to the principle of welding equal strength: automatic submerged arc welding, the welding material grade is H08MuA , the diameter of the electrode is 4.0mm and 5.0mm ; the flux grade is HJ431 , the specification is 0.4 ~ 2.5 mm , the flux must be baked at a temperature of 250 °C and kept warm for 1 ~ 5 hours before use .
The welding grooves of the longitudinal and circumferential welds of the steel pipe are processed in the form of asymmetric " X ", and the " X " shaped groove is conducive to the control of welding deformation. That is to say, 2/3 of the asymmetric " X " groove is opened on the outer side of the upper part above the horizontal centerline of the steel pipe and the inner side of the lower part below the horizontal centerline of the steel pipe, so that the large groove faces upwards, so as to facilitate the welding operation and welding quality of the on-site installation weld guarantee.
In the welding process, in order to reduce welding deformation and shrinkage stress, ① 4.0mm electrode is used for bottom welding, and ① 5.0mm electrode is used for interlayer filling . When welding, pay attention to ensuring symmetry and multi-layer multi-pass welding. The microstructure of multi-layer multi-pass welding joints is finer, the heat-affected zone is narrow, and the ductility and toughness of the joints are relatively good. When welding longitudinal seams of steel pipes, two longitudinal The joints are welded at the same time and the welding speed is as consistent as possible, so that the welding preheat received by each different side during the welding process can be balanced. Generally, welding on a component should start from a position that is relatively fixed relative to the component, and progress to a welding point that has a greater degree of freedom of movement and is estimated to have less shrinkage and less constraints as much as possible; when welding a constrained weld, the welding should not be terminated or welded. To the welds with the lowest approved preheat and interpass temperature to ensure that the welds do not crack.
Choosing the right welding parameters is the key to ensure the welding quality. Appropriate selection of welding parameters can not only make the arc stable, the penetration is good, the weld shape is beautiful, the shape and size of the weld are appropriate, and there are no defects such as pores, slag inclusions, cracks and incomplete penetration, it can also improve welding productivity and reduce welding costs. . Welding procedure qualification shall be carried out before formal welding of steel coil pipe, and welding parameters and welding sequence shall be formulated according to the welding procedure qualification report. ① The main process parameters shown in Table 2 are used for submerged arc welding of 4200x40mm steel coil pipe.
Table 2 ① 4200 x 40mm steel coil pipe submerged arc welding welding process parameters

Weld Type	Welding current /A	Arc voltage /V	Welding speed / ( mm/min )
Inside	850 ~ 900	34 ~ 36	200 ~ 250
straight seam
outside	950 - 1000	36 ~ 38	250 ~ 300
Inside	850 ~ 900	34 ~ 36	200 ~ 250
circular seam
outside	900 ~ 950	36 ~ 38	250 ~ 300

The steel coil pipe is mainly submerged arc automatic welding, supplemented by manual welding. The welding is carried out on the longitudinal seam welding platform. The welding should pay attention to: ① When welding, the arc should be started and rested on the groove, and the arc should not be started on the base metal , The arc crater should be filled up when the arc is stopped; ②Strictly adopt the welding process and selected parameters of symmetrical segmental step-back welding.
Arrangement of welding sequence: first weld 50% of the asymmetric " X " shaped large groove side , and then transfer to the asymmetric " X " shaped small groove side, carry out carbon arc gouging, grinding, welding, and the small After welding 75% of the weld seam at the groove (only the cover weld bead remains), turn to the large groove side, weld 75% of the weld seam on the large groove side , and finally weld

3.5 Weld inspection requirements
①Appearance inspection shall be carried out after the first and second types of welds are welded, and non-destructive testing shall be carried out only after the appearance inspection is qualified. ②Non-destructive testing is guaranteed to be carried out after 24 hours (after welding). ③ The non-destructive testing results shall be submitted to the supervisor within 48 hours after the inspection is completed. ④Ultrasonic flaw detection is evaluated according to the standard GB11345-1989 "Manual Ultrasonic Flaw Detection Methods and Flaw Detection Results for Steel Welds". Class I welds are qualified at BI level, and Class II welds are qualified at BI level. Radiography and Quality Grading of Welded Butt Joints" standard is implemented, Class II welds are qualified, and Class II welds are qualified Class III .
The steel coil pipe welds produced by the above process all meet the first-class welding seam standard through appearance inspection and internal non-destructive testing, and the mechanical performance test results meet the requirements of the national standard ( GB700-88 ) .
4 Conclusion
On March 10 , 2010 , the steel coil pipe production officially started, and on December 25 , 2010 , the production task was successfully completed. Practice has proved that this technology meets the requirements of design and construction, solves the traditional industry requirements of rolling production in professional processing workshops or factories, saves costs, improves efficiency, and meets the requirements of on-site construction progress.
The use of this process is conducive to improving the mechanized production level of steel coil pipes, greatly reducing the technical requirements of the workers involved in the production, making the original non-standard processing into industrial production of factory-like assembly lines, effectively improving production efficiency and ensuring project quality. . At the same time, the operating conditions have been improved to achieve safe production. According to this process, the daily output of coiled steel pipes can reach 150 ~ 180t , which satisfies the needs of the project well.
The successful application of this project has accumulated valuable experience for the production of large-diameter non-standard steel coil pipes, and has certain reference significance for other similar projects.

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