3.1.1 Submerged arc welding process
Manufacturing process for straight seam welded pipe
Pipe manufacturing process and main equipment
Steel plate → Vacuum lifting → Ultrasonic testing of steel plate → Milling → Pre bending
J forming → C forming → O forming
After the conveyor roller transports the steel plate to the oil pressure bed for positioning, the first time 1/3 of the width of the plate is formed by the upper and lower molds, which is called "J forming"; The other end of the second molding is 1/3 of the board width, known as "C-molding"; Finally, the remaining 1/3 of the board width is formed from the center of the board, resulting in a circular tube shape called "O forming".
a) "O" stamping forming b) "C" stamping forming c) "J" stamping forming
Figure.3 Schematic diagram of UO (UOE) forming process
Figure.4 Schematic diagram of RB (RBE) forming process
Comparison of JCO and UO molding methods:
JCO forming is a progressive pressure forming process that transforms the forming process of steel pipes from two steps of UO forming to multiple steps. During the forming process, the steel plate undergoes uniform deformation, low residual stress, and no scratches on the surface. The processed steel pipe has greater flexibility in the size range of diameter and wall thickness, which can produce both large and small batches of products; It can produce both large-diameter high-strength thick walled steel pipes and small-diameter large walled thick steel pipes; Especially in the production of high steel grade thick walled pipes, especially small and medium-sized thick walled pipes, it has advantages that cannot be compared to other processes. It can meet more requirements of users in terms of steel pipe specifications. Low investment, but low production efficiency, with a typical annual output of 100000 to 250000 tons.
UO molding, using two pressure forming processes of U and O, is characterized by high capacity and high output, typically reaching an annual output of 300000 to 1 million tons, suitable for large-scale production of a single specification. The investment is large and generally difficult for developing countries to bear.
Ultrasonic inspection equipment: Ultrasonic inspection of the weld bead is required before and after the water pressure test.
High frequency straight seam welded steel pipe, also known as straight seam resistance welded pipe, is generally produced with a smaller diameter, usually below DN600. Large diameter steel pipes are generally double-sided submerged arc welded. Its characteristics are: high welding speed, small welding heat affected zone, no cleaning of the workpiece during welding, and welding of thin-walled pipes.
1) Differences in raw materials and production capacity
The raw material of ERW steel pipe is hot-rolled steel coil, while the raw material of UOE steel pipe is cold-rolled steel plate. Therefore, ERW steel pipes can achieve continuous assembly line operations with high production efficiency and low production costs; UOE steel pipes are processed using steel plates, which cannot achieve continuous assembly line operations, resulting in low production efficiency and high production costs.
2) Welding differences
ERW steel pipe welding does not require the addition of welding wires; UOE steel pipes require the addition of welding wires.
3) Product differentiation
ERW steel pipes are limited by the thickness of the steel coil, with a maximum thickness of 25mm and a maximum diameter of 660mm that can be produced; The maximum thickness that UOE steel pipes can produce is 40mm, and the maximum diameter that can be produced is only limited by the width of the steel plate. Currently, the maximum diameter that can be produced is 1422mm.
4) Application differences
ERW steel pipes are mainly used in long-distance land pipelines such as natural gas, refined oil, crude oil, and mineral slurry. UOE steel pipes are mainly used in high-pressure subsea long-distance pipelines, high-altitude cold areas, etc.
Uncoiling → Leveling → Shear Butt Welding → Looper Storage → Plate Exploring → Trimming → Roller Forming → High Frequency Welding → Removing Inner and Outer Burrs → Online Ultrasonic Testing → Intermediate Frequency Annealing → Air Cooling → Water Cooling → Sizing → Straightening → Cutting → Initial Inspection of Dimensions and Appearance → End Repair → Hydrostatic Testing → Full Pipe Ultrasonic Testing → Offline Weld Ultrasonic Testing → Pipe End Ultrasonic Testing → Final Inspection of Dimensions and Appearance → Application of Anti-rust Paint → Spray Marking → Pipe End Protection → Comprehensive Inspection And warehousing.
The uncoiler, leveling machine, shear welding machine, and storage bin are essential equipment for the uninterrupted supply of steel strips to the forming machine and improving production efficiency.
Cutting and butt welding machine: Cut and butt the tail of the previous steel coil with the head of the subsequent steel coil.
Loop storage device: The loop is an indispensable and important equipment to ensure the automatic production of high-frequency straight seam welded pipes, playing a role in ensuring the storage, supply, and continuous operation of the main rolling mill. As shown in the following figure.
Figure.5 High frequency welding loop material storage device
Forming process (rolling tube): The deformation of the plate in the process of forming the tube is mainly manifested in two aspects: continuous transverse and longitudinal, and the constraint force applied on it is implemented through two aspects: the roll pass and the arrangement of the rolling mill. The roll pass causes transverse deformation of the steel plate, and the rolling mill arrangement causes longitudinal deformation of the steel plate. The following figure shows the forming process of welded pipes.
Figure.6 Schematic diagram of welded pipe forming process
High frequency welding: By utilizing the skin effect of high-frequency current, high-frequency electrical energy can be concentrated on the surface of the welding piece, and by utilizing the proximity effect, the position and range of the high-frequency current flow path can be controlled. When high frequency current is required to be concentrated in a certain part of the weldment, this requirement can be achieved by forming a current circuit between the conductor and the weldment and making the conductor close to this part of the weldment so that they form adjacent conductors with each other. High frequency welding is based on the specific form and special requirements of the weldment structure, mainly using the skin effect and proximity effect to quickly heat the surface metal of the weldment to be welded and achieve welding. As shown in the following figure.
Figure.7 Schematic diagram of high-frequency welding
There are many methods for quality inspection of straight seam welded pipes, among which the physical method is also the most commonly used inspection method. Physical inspection is a method that uses some physical phenomena for measurement or inspection. The inspection of internal defects in materials or Q235B straight seam welded pipes is generally carried out using non-destructive testing methods. The current non-destructive testing methods include magnetic testing, ultrasonic testing, radiographic testing, penetration testing, etc.
The use of straight seam welded pipes is very extensive, mainly including the following aspects:
Overall, straight seam welded pipes have good strength and durability, and are widely used in various engineering and industries to meet the needs of conveying and discharging liquids and gases.
Spiral welded pipes generally have higher strength than straight seam welded pipes, and can produce larger diameter welded pipes using narrower billets. Additionally, welded pipes with different diameters can be produced using billets of the same width. However, compared to straight seam pipes of the same length, the weld length increases by 30-100% and the production speed is lower. Therefore, smaller diameter welded pipes mostly use straight seam welding, while larger diameter welded pipes mostly use spiral welding.
6.1 Comparison of welding processes
The production process of straight seam steel pipes is relatively simple, mainly including high-frequency straight seam welded pipes and submerged arc welded straight seam welded pipes. High frequency straight seam welding of steel pipes is achieved by rolling a certain specification of long steel strip into a circular tube through a high-frequency welding machine and welding the straight seam. High frequency welding is a type of induction welding (or pressure contact welding) that does not require weld filler material, has no welding spatter, narrow welding heat affected zone, beautiful welding shape, and good welding mechanical properties. Therefore, it is widely used in the production of steel pipes. Connected into a steel pipe. The shape of steel pipes can be circular, square or irregular, depending on the sizing and rolling after welding. Straight seam welded pipe has high production efficiency, low cost, and rapid development. The straight seam submerged arc welded steel pipe has one longitudinal weld seam, and both the inner and outer welds are welded using one submerged arc welding process. After overall mechanical expansion treatment, the internal stress of the steel pipe is small and evenly distributed, which can effectively prevent stress corrosion cracking. The dimensional accuracy is high, and it is convenient for on-site welding construction. The process of pre welding and fine welding is adopted, which ensures stable welding process and high weld quality. Welds are easy to achieve non-destructive testing during production and field non-destructive testing during use. The product has a wide range of specifications, which can produce both small diameter and large wall thickness steel pipes. The pipe diameter is limited by the width of the steel plate, and a steel plate of one width can only produce a steel pipe of one diameter.
The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Spiral seam submerged arc welded pipes do not have 100% ultrasonic testing of the base material, expansion and other processes, resulting in low production and difficulty in automatic tracking of welds. Forming and welding are all completed under continuous dynamic operation; Continuous production can be achieved, and larger diameter welded pipes can be produced using narrower billets. Welded pipes with different diameters can also be produced using billets of the same width. However, compared to straight seam pipes of the same length, the weld length increases by 30-100% and the production speed is lower. Therefore, smaller diameter welded pipes mostly use straight seam welding, while larger diameter welded pipes mostly use spiral welding.
In terms of welding process, the welding method for spiral welded pipes and straight seam steel pipes is the same (submerged arc welding), but straight seam welded pipes inevitably have many T-shaped welds, which greatly increases the probability of welding defects. Moreover, the welding residual stress at the T-shaped weld is relatively high, and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracks.
In China, smaller diameter welded steel pipes mostly use straight seam welding, while larger diameter welded steel pipes mostly use spiral seam welding. Currently, China has the ability to produce large diameter straight seam submerged arc welded steel pipes and has been used in oil and gas transportation projects.
6.2 Comparison of Material Properties
Straight seam submerged arc welded pipes are produced from steel plates, while spiral welded pipes are produced from hot-rolled coils. The rolling process of the hot rolled strip mill has a series of advantages, including the ability to obtain metallurgical processes for producing high-quality pipeline steel. For example, a water cooling system is installed on the output stage to accelerate cooling, which allows the use of low alloy components 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 coil plates is often lower than that of similar grade steel plates, which also improves the weldability of spiral welded pipes. It should be noted that due to the fact that the rolling direction of the spiral welded pipe is not perpendicular to the axis of the steel pipe (its clamping depends on the spiral angle of the steel pipe), and the rolling direction of the steel plate of the straight seam steel pipe is perpendicular to the axis of the steel pipe, the crack resistance performance of the spiral welded pipe material is better than that of the straight seam steel pipe.
Moreover, according to the process regulations of submerged arc welding, each weld seam should have a starting and extinguishing point, but each straight seam welded pipe cannot meet this condition when welding the circumferential seam, so there may be many welding defects at the extinguishing point.
6.3 Comparison of structural strength
When welded pipes are subjected to internal pressure, they usually generate two main stresses on the pipe wall, namely radial stress and axial stress, and the weld joint is subjected to composite stress. Due to the different shapes of the weld seam, the combined stress at the spiral weld seam is 60-85% of the main stress of the straight welded pipe when subjected to internal pressure. Therefore, under the same working pressure, the wall thickness of spiral welded pipes with the same diameter can be reduced compared to straight welded pipes.
6.4 Quality Comparison and Analysis
6.4.1 Advantages and disadvantages of spiral seam submerged arc welded pipes
Disadvantages of spiral seam submerged arc welded steel pipes
Advantages of spiral seam submerged arc welded pipes
6.4.2 Advantages and disadvantages of straight seam submerged arc welded pipes
Disadvantages of straight seam submerged arc welded pipes
Advantages of straight seam submerged arc welded pipes
In today's rapidly developing industrial market, purchasing straight seam welded pipes is an essential part of many industries. Whether in the construction, manufacturing, or oil and gas industries, straight seam welded pipes play a crucial role. To ensure that you can obtain the highest quality products and meet the needs of the project, it is crucial to understand how to purchase straight welded pipes effectively.
1. Determine requirements and specifications
Before purchasing straight seam welded pipes, it is necessary first to clarify the specific requirements and specifications of the project or business. This includes the size, material, thickness, and required quantity of the pipeline. Understanding these key elements will help you better communicate with suppliers and choose the product that best suits your needs.
2. Looking for reputable suppliers
Choosing a reputable supplier is a crucial step in ensuring high-quality straight seam welded pipes are obtained. You can evaluate its credibility by referring to customer reviews, industry reputation, and supplier certification qualifications. Communicate with multiple suppliers to understand their product quality, delivery time, after-sales service and make trade-offs.
3. Considering product quality and certification
Ensuring that straight seam welded pipes comply with international and industry standards is an important aspect of ensuring engineering quality. Choosing products that comply with ISO 9001 quality management system certification will help ensure that you receive high-quality products. At the same time, understanding the supplier's quality management system and product quality control process is also a crucial step.
4. Consider delivery time and logistics arrangements
Timely delivery and good logistics arrangements are crucial when purchasing straight seam welded pipes. Confirm the production cycle, delivery time, and transportation method of the product with the supplier, and ensure that they can deliver the product on time. Meanwhile, for large-scale engineering projects, reasonable planning of logistics arrangements is also one of the important factors to ensure the smooth progress of the project.
5. Price comparison and negotiation skills
Price is one of the important factors that must be addressed in the procurement process. When considering the procurement cost of straight seam welded pipes, it is recommended to compare prices with multiple suppliers and comprehensively consider different factors such as product quality and delivery time. Mastering certain negotiation skills and actively communicating and negotiating with suppliers on prices, delivery conditions, and other aspects can help you obtain more competitive prices and more favorable procurement conditions.
We cannot blindly pursue low prices and diverse comparisons. If low-quality steel pipes are used for a long time, they may rust, crack, and other unsafe situations. So, cost-effectiveness is a key factor that we need to consider.
How to control the price when purchasing straight seam welded pipes?
Straight seam welded pipe is a widely used steel pipe product. When purchasing straight seam welded pipes, controlling the price is crucial. Therefore, here, we share some tips on controlling the price of straight seam welded pipes and improving procurement efficiency.
6. After-sales service and warranty terms
Ensuring that suppliers provide good after-sales service and reasonable warranty terms is an important link in ensuring procurement quality and subsequent maintenance. Communicate clearly with suppliers about after-sales service policies, product warranty periods, and after-sales support measures, which will bring more convenience and guarantee for your subsequent use and maintenance.
In summary, by reasonably planning the procurement process, selecting reputable suppliers, ensuring product quality and delivery time, flexibly using negotiation skills, and paying attention to after-sales service and warranty terms, you will be able to purchase high-quality straight seam welded pipes that meet the requirements more efficiently, and inject stable support and guarantee into your engineering project.
When purchasing straight seam welded pipes, you can consider yaang. As a manufacturer of straight welded pipes, yaang have the following advantages:
Choosing yaang's straight seam steel pipes not only saves costs and improves efficiency but also ensures the smooth progress of your engineering project. We look forward to working with you to create a better future together!
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