Successful delivery of spiral pipes for water supply in Ecuador

 Over the past five years, we have maintained close business cooperation with our north American customers. During the cooperation, we have exchanged industry knowledge, discussed project solutions and provided perfect products and services for many projects.

In December 2018, we received an active enquiry from a customer in North America again. The customer needed API 5L PSL1 Grade B spiral pipe for the water supply project. The first time we received the inquiry, we quickly reported the project plan to the customer.

From the follow-up project follow-up, I learned that this project is a local water pipeline project, which requires anti-corrosion coating, internal anti-corrosion epoxy paint 300 microns, external anti-corrosion 3PE 2.5 mm.

During a long time negotiation on the price, payment term, coating, standard and production control, order was finalized successfully.We processing the production strictly according to client’s request and finally deliver all goods in time.

Because the pipes have inner and outer coatings, when the pipes need to be packed in the port, we consult with the freight forwarder many times to protect the coating from being damaged. Finally, we choose to pad the cartons around the container and the contact points between the pipes to protect the outer coatings, and protect the packing tools with wrapping cloth to prevent the damage of the inner coatings.

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Concrete analysis of the production process steps of spiral tubes

　　Spiral tube production process steps

　　(1) The spiral pipe raw material is a ribbon coil, a welding wire, and a flux. Strict physical and chemical testing is required prior to input.

　　(2) The steel head and the tail are butt jointed, and single or double-line submerged arc welding is adopted. After the steel pipe is rolled, automatic submerged arc welding is adopted.

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

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

　　(5) The spiral tube is formed by external control or internal control roll forming.

　　(6) Weld control device is used to ensure that the weld meets the welding requirements, strictly control the pipe diameter, the misalignment and the weld gap.

　　(7) Both internal and external welding are performed by single or double wire submerged arc welding of American Lincoln welding machines to obtain stable welding specifications.

　　(8) The welds are all online continuous ultrasonic automatic injury detection to ensure non-destructive testing of 100% spiral welds. If there is a defect, the alarm will automatically alarm and spray, and the production worker can adjust the process parameters at any time to eliminate the defects.

　　(9) The spiral tube is cut into a single piece by an air plasma cutting machine.

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

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

　　(12) The butt weld pipe of the strip and the butt joint that intersects the spiral weld are inspected by X-ray television or film.

　　(13) A hydrostatic test was performed on each of the spiral tubes, and the pressure was radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. Automatically print and record test parameters. The tube ends are machined to precisely control the end face perpendicularity, groove angle and blunt edge.

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Advantages of Submerged Arc Welding Spiral Steel Pipe

　　In the spiral pipe production process and the use, there are invented a lot of excellent welding and methods of production, greatly contributed to the steady and rapid development of the industry, but also makes this industry has been optimized in development. Which submerged arc welding is a welding method in a new invention in 1940, it and the front of the place is the same manual welding or the use of slag to protect it, but this is not the slag electrode coating, is designed smelting flux out. Changed after the wire, the wire delivery device with a plate and the wire, the wire is continuously sent, this welding wire is fed continuously in a granular fusible flux covering ignition arc welding wire, base material and part of the melting and evaporation flux forms a cavity, the arc is stable combustion in the cavity inside, so call it submerged arc welding. Arc is buried in the inside of the cavity. The welding flux hopper loading system consists of a drug delivery through a pipe to be welded to the front of the second type of welding is used, the use of wire, since the wire can be continuously sent; Rod, a rod that we must have a burn a welding head gave the throw, and the operation was stopped, and then change electrode welding.

　　And such welding method compared with other methods is the great advantage, the first advantage is fully automated; the second advantage, which is buried Under arc welding, so it's the heat exchange and protection of relatively strong performance, high quality welding out; third advantage, because the submerged arc welding arc buried in the flux, so it can be used a large current, welding efficiency relatively high.

Causes of trachoma weld formation

　　Spiral Pipe(ssaw steel pipe): by strip by roll forming machine, folding spiral direction, and then double-sided submerged arc welding is made through a capacitor. Spiral welded steel pipe production process, prone to leakage in many cases, such as welding and the wrong side. However, in these cases appear Chlamydia is the most difficult to master spiral steel butt weld.

　　The so-called trachoma: that the welding process on the inside surface of the weld or welds, there has not been a thorough penetration of particles or bubbles, as well as the shape of the sand pit in the surface of the weld. The reason for trachoma are the following:

　　1, the supply of the welding torch during the current is too small, the capacitor is too short, the capacitor has not been completely thorough when welding the welding surface has been hardened, so there occurs a penetration of sand or not bubbles.

　　2, scimitar tune into the strip-shaped curvature of the time there is no good butt, butt strip does not match exactly, there has been too much of a gap between the butt strip.

　　3, butt welded steel when the two sides have not cleared up the edge of the strip rust or scale.

　　4, there is no timely maintenance of production equipment to clean up. Workbench dust or dirt, mistakenly fall into the gap at the butt welding of steel.

　　5, the operating temperature is too low or too wet workshop, which affects the temperature and dryness of welding points.

Thick-walled Spiral Pipe Steel Grades

　　In the pipeline pressure ratio is also gradually reduced.Optimized calculation, comparison and selection of diameter, pressure and pressure ratio requirements.When determining the amount of input, determine the diameter, pressure, pressure ratio by optimizing the future, such as selecting a higher pressure steel strength grade is too low, it will cause excessive wall thickness, which gives the pipe, site welding and transportation links with many other be difficult, or even difficult to achieve.

　　Now more choice of fluid pipes thick-walled spiral pipe, pipeline delivery pressure medium is gradually increased in recent years, especially in the gas pipeline online. This is because in a certain range to improve the delivery pressure will increase economic efficiency, to pipe gas pipeline, for example, in the same amount of input conditions, increases the density of the gas delivery pressure and increase the flow rate is reduced, so that the friction resistance decreased.

　　Production needs to promote the improvement of the steel grade. The so-called pressure ratio refers to the ratio of inbound and outbound pressure pressure, the pressure ratio across the board reduction means are operating at a higher pressure, so that power consumption can also be reduced. Early pressure is more than 1.6, and later fell to 1.4 in recent years, some foreign gas pipeline to take pressure ratio was 1.25. Of course, the pressure ratio decreases, the number of compressor stations to increase, so that investment will increase.

Quality Inspection of Spiral Pipe

　　Before the mechanical performance test, flattening test and expansion test, the screw pipe factory should carry out the test first and meet the standard requirements. Straight seam steel quality inspection method is as follows:

　　1, From the face of it, that is visual inspection. Visual inspection of welded joints is a simple procedure but widely used test method is an important part of product testing, the main defects and deviations are found on the surface of the weld size. Usually by the naked eye, with the standard model, gauge and test tools such as a magnifying glass. If the weld surface defects, weld defects there may be internal.

　　2, Physical test methods: physical test method is to use some physical phenomena assay or test method. Or within the workpiece material defect inspection, and are generally used NDT methods. NDT ultrasonic flaw detection, radiation detection, penetration testing, magnetic testing and so on.

　　3, Pressure vessels strength test: pressure vessels, in addition to tightness test, but also the strength test. There are common test of two hydraulic test and air pressure. They can be tested in working under pressure vessels and piping welds compactness. Hydrostatic pressure test is more sensitive than the test speed and, at the same time after the test products do not waste water treatment, drainage problems for the product is particularly applicable. But the risk is greater than the test pressure test. When tested, it must comply with the appropriate safety measures to prevent accidents during the test.

　　4, Compact test: liquid or gas storage vessel welding, which is not dense weld defects, such as penetrating cracks, pores, slag, incomplete penetration loose tissue and the like, can be used to find the density test. Compactness test methods are: kerosene test, carrying water testing, water will test etc.

　　5, Hydrostatic test: each pipe hydrostatic test should be done without leakage test pressure press Calculate P = 2ST / D where S- hydrostatic test stress test Mpa, hydrostatic test stress testing in accordance with corresponding steel standard specifies the minimum degree of yield (Q235 is 235Mpa) 60% of the selection.

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How to check the quality of spiral steel tube

　　Spiral pipe factory should be done before the mechanical performance test and flattening test, and flaring test, and to achieve the standard requirements. Spiral steel pipe quality inspection method is as follows:

　　1, From the face of it, that is visual inspection. Visual inspection of welded joints is a simple procedure but widely used test method is an important part of product testing, the main defects and deviations are found on the surface of the weld size. Usually by the naked eye, with the standard model, gauge and test tools such as a magnifying glass. If the weld surface defects, weld defects there may be internal.

　　2, Physical test methods: physical test method is to use some physical phenomena assay or test method. Or within the workpiece material defect inspection, and are generally used NDT methods. NDT ultrasonic flaw detection, radiation detection, penetration testing, magnetic testing and so on.

　　3, Pressure vessels strength test: pressure vessels, in addition to tightness test, but also the strength test. There are common test of two hydraulic test and air pressure. They can be tested in working under pressure vessels and piping welds compactness. Hydrostatic pressure test is more sensitive than the test speed and, at the same time after the test products do not waste water treatment, drainage problems for the product is particularly applicable. But the risk is greater than the test pressure test. When tested, it must comply with the appropriate safety measures to prevent accidents during the test.

　　4, Compact test: liquid or gas storage vessel welding, which is not dense weld defects, such as penetrating cracks, pores, slag, incomplete penetration loose tissue and the like, can be used to find the density test. Compactness test methods are: kerosene test, carrying water testing, water will test.

　　5, The hydrostatic test should be done each pipe hydrostatic test without leakage, pressure test press Calculate P = 2ST / D where S- hydrostatic test stress test Mpa, hydrostatic test stress test according to the corresponding steel standard specifies the minimum degree of yield (Q235 is 235Mpa) 60% of the selection. Regulators time: D <508 test pressure holding time less than 5 seconds; D≥508 test pressure holding time less than 10 seconds 4, non-destructive testing of steel welding seam, strip end weld and circumferential joints should X-ray or ultrasonic inspection. For ordinary combustible fluid transport spiral steel to weld should be 100% SX-ray or ultrasound test, used for water, sewage, air, heating steam and other general transmission fluid with spiral weld steel pipe should be X-rays or ultrasonic inspection checks (20%).

　　The spiral steel pipe quality test results, spiral pipe usually divided into three categories: Qualified, rework and scrap. Qualified means the quality and appearance of the intrinsic quality to meet the standards or technical delivery and acceptance conditions spiral steel pipe; rework refers to the quality and appearance of the intrinsic quality does not fully comply with the acceptance criteria and strip body, but allow the repair after repair can meet the standards and acceptance conditions spiral pipe; waste refers to substandard quality and appearance of the intrinsic quality of spiral steel still not up to standard and acceptance conditions do not allow repair or rework later.

Difference between saw and erw pipe

    First, difference between the production process

    ERW pipe is the hot-rolled coil through the continuous roll forming, the use of high-frequency current skin effect and proximity effects, so that the plate edge of the hot melt, squeezing the roller pressure to the role of pressure welding achieve production. Therefore, the residual stress of the erw pipe is small, and the residual stress is further released and reduced through the processes of heat treatment, sizing, straightening and water pressure of the weld. Practice has proved that, erw pipe in the storage and use of residual stress on the pipe does not affect. Without any wire, the weld is physically and chemically identical to the plate. The quality of the erw pipe depends on the quality of the sheet.

    SAW pipe through the unit screw spiral welding together, the plate through the spiral rotation, so that the geometric stress more complex, and some even reached the yield limit of the steel, spiral pipe after the formation of a larger residual stress, the residual stress is tensile stress. The steel by the internal pressure, the wall also produces a circumferential tensile stress, the two superposition, so that steel can withstand capacity weak. More insecure during use. Steel plates are welded together by a wire with a chemical composition that is prone to air bubbles and weld bead cracks during the welding process. So that the weld and base metal in the physical properties and chemical composition of the apparent difference. Easily in the weld with the base metal joints have a great concentration of stress. In the welding process, thermal effects, and high hardness.

    Second, difference between raw materials

    The raw materials used by erw pipe are all hot-rolled coils produced by regular manufacturers with relatively stable chemical composition and physical properties.

    Most of the raw materials used in the spiral pipe mill are low-grade hot-rolled steel strip, with unstable chemical composition, physical properties and internal defects and impurities.

    Third, the procurement costs and procurement difficulties

    Spiral steel pipe production of large-scale steel pipe plant of petroleum and petrochemical systems, the advantages are mainly concentrated in the manufacture of large-diameter steel pipe, the manufacturing cost is relatively low. However, for small and medium caliber (Φ114mm ~ Φ355.6mm) steel pipe, the manufacturing cost is higher, averaging 8% ~ 15% higher than ERW pipe.

    Large-scale spiral pipe plant often do not produce small and medium-sized spiral pipe, procurement more difficult. Medium and small diameter erw pipe, due to the large number of manufacturers, is very easy to purchase.

    Fourth, pipe geometry

    1, ERW pipe geometry of the higher accuracy; and spiral welded pipe geometry accuracy is low, resulting in the construction of the site weld girth difficulties.

    2, ERW pipe weld coefficient is 100%; spiral welded pipe weld coefficient of 130% -200%. The weld length of spiral pipe is much longer than that of erw pipe, and the incidence of defects also increases synchronously.

    3, ERW pipe weld height remaining close to zero, the naked eye is not visible; spiral steel pipe on the outside surface must leave about 0.3 mm height (which is determined by the production process). The weld seam is so high that there is a gap between the steel pipe coating (3PE) and the pipe body, which makes the corrosion resistance of the steel pipe greatly reduced.

    4, Due to the spiral welded pipe remaining high, the transmission of high-speed fluid there will be a greater disturbance, increase the flow resistance and reduce pipeline delivery efficiency. ERW pipe wall smooth, then there is no such problem.

    Five, other differences

    ERW pipe compression performance is higher than the spiral pipe.

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