Product knowledge sharing of SSAW Steel Pipe

1.What is an SSAW steel pipe?

SSAW steel pipe: it is made by rolling low-carbon structural steel or low-alloy structural steel strip into pipe blank according to a certain angle of the spiral line (called forming angle), and then welding the pipe seam. It can produce large-diameter steel pipe with narrow strip steel. The specification is expressed by outer diameter * wall thickness. The welded pipe shall ensure that the hydrostatic test, tensile strength, and cold bending performance of the weld meet the requirements.

2.Production process of SSAW steel pipe

SSAW steel pipe is also a kind of welded pipe equipment. Its strength is generally higher than that of straight welded pipe. It can produce welded pipes with larger pipe diameters with narrow blank and welded pipes with different pipe diameters with blank of the same width. However, compared with the straight seam pipe with the same length, the weld length increases by 30 ~ 100%, and the production speed is low. Therefore, straight seam welding is mostly used for small-diameter welded pipes, and spiral welding is mostly used for large-diameter welded pipes.

The production process of SSAW: it is a spiral seam steel pipe welded by automatic double-wire double-sided submerged arc welding process with strip steel coil as raw material, often warm extrusion forming.

◆ raw materials, i.e. strip steel coil, welding wire, and flux. Strict physical and chemical inspections shall be carried out before input.

◆ butt joint of strip steel head and tail, single wire or double wire submerged arc welding shall be adopted, and automatic submerged arc welding shall be adopted for repair welding after rolling into the steel pipe.

◆ before forming, the strip steel shall be leveled, trimmed, planed, surface cleaned, transported, and pre-bent.

◆ 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 strip steel.

◆ adopt external control or internal control roll forming.

◆ the weld gap control device is used to ensure that the weld gap meets the welding requirements, and the pipe diameter, misalignment, and weld gap are strictly controlled.

◆ American Lincoln electric welder is used for single wire or double wire submerged arc welding for internal and external welding, to obtain stable welding specifications.

◆ all welded welds are inspected by an online continuous ultrasonic automatic flaw detector to ensure 100% NDT coverage of spiral welds. If there are defects, it will automatically alarm and spray marks, and the production workers will adjust the process parameters at any time to eliminate the defects in time.

◆ cut the steel pipe into single pieces by air plasma cutting machine.

◆ after cutting into a single steel pipe, the first three steel pipes in each batch shall be subject to a strict first inspection system to check the mechanical properties, chemical composition, fusion condition, steel pipe surface quality, and NDT. Only after the pipe-making process is qualified can it be officially put into production.

◆ the parts with continuous acoustic flaw detection marks on the weld shall be rechecked by manual ultrasonic and X-ray. If there are defects, after repair, they shall be subject to NDT again until it is confirmed that the defects have been eliminated.

◆ the butt weld of strip steel and the pipe where the T-joint intersects with the spiral weld shall be inspected by X-ray television or film.

◆ each steel pipe is subject to a hydrostatic test, and the pressure is sealed radially. The test pressure and time are strictly controlled by the microcomputer detection device of steel pipe water pressure. Test parameters are automatically printed and recorded.

◆ the pipe end is machined to accurately control the end face’s perpendicularity, slope angle, and blunt edge.

Anti corrosion spiral welded pipe technology

Because the individual quality of spiral welded pipe is relatively large, it must be stacked outdoors, but it is difficult to avoid being exposed to the sun and rain. Therefore, the problem of rust has been perplexing the storage time and conditions of spiral welded pipe. Therefore, we must give a comprehensive answer to the rust prevention knowledge of spiral welded pipe.

The steel surface is mainly polished with tools such as steel wire brushes. The loose or warped oxide scale, rust, and welding slag can be removed by cleaning and preheating of spiral welded pipe. The derusting of manual tools can reach grade SA2 and that of power tools can reach grade SA3. If the steel surface is firmly attached with an iron oxide scale, the derusting effect of tools is not ideal and can not reach the anchor depth required for anti-corrosion construction.

Pickling uses solvent and emulsion to clean the surface of welded steel pipe (welded pipe) for low-pressure fluid transmission, to remove oil, grease, dust, lubricant, and similar organics, but it can not remove rust, oxide scale, and welding flux on the steel surface, so it is only used as an auxiliary means in anti-corrosion production.

Generally, chemical and electrolytic methods are used for pickling treatment. Only chemical pickling is used for pipeline anti-corrosion, which can remove oxide scale, rust, and old coating. Sometimes it can be used as reprocessing after sandblasting. Although chemical cleaning can make the surface reach certain cleanliness and roughness, its anchor lines are shallow, and it is easy to pollute the stacking environment of spiral welded pipes.

3.Application of SSAW steel pipe

Generally used for: welding pipeline, conveying fluid, metal structure, pile, etc. The products are widely used in water conservancy engineering, petrochemical industry, chemical industry, electric power, agricultural irrigation, urban construction and other fields. Spiral immersed steel pipe is one of the 20 key development products for conveying liquid: water supply and drainage. For gas transportation: gas, steam, liquefied petroleum gas. Structural use: piling pipe, bridge; Piers, roads, buildings, and other structural pipes

4.Advantages and disadvantages of SSAW steel pipe

Advantages of SSAW steel pipe:

◆ steel pipes with different diameters can be produced by using strip steel with the same width, especially steel pipes with large diameters can be produced by narrow-band steel.

◆ under the same pressure condition, the stress of spiral weld is smaller than that of the straight seam, which is 75% ~ 90% of that of straight seam welded pipe, so it can bear large pressure. Compared with the straight welded pipe with the same outer diameter, the wall thickness can be reduced by 10% ~ 25% under the same pressure.

◆ the dimension is accurate. Generally, the diameter tolerance is no more than 0.12%, the deflection is less than 1 / 2000, and the ovality is less than 1%. Generally, the sizing and straightening processes can be omitted.

◆ it can be produced continuously. Theoretically, it can produce infinite steel pipe with small head and tail cutting loss and can improve the metal utilization rate by 6% ~ 8%.

◆ compared with straight welded pipe, it has the flexible operation and convenient variety change and adjustment.

◆ light equipment weight and less initial investment. It can be made into a trailer-type mobile unit to produce welded pipes directly at the construction site where the pipes are laid.

◆ easy to realize mechanization and automation.

The disadvantages of SSAW steel pipe:

Due to the use of rolled strip steel as raw material, there is a certain crescent curve, and the welding point is in the elastic strip steel edge area, so it is difficult to align the welding torch and affect the welding quality. Therefore, complex weld tracking and quality inspection equipment should be set up.

5.How to check the quality of SSAW steel pipe？

◆ production and management

The production of SSAW steel pipe can reflect the advantages of high quality and high efficiency. The production capacity of a spiral welded pipe unit is equivalent to 5-8 longitudinal welded pipe equipment. How to make multiple pipe rolling equipment production lines meet the same manufacturing standard, that is, according to the unified production process specification and quality assurance system, so as to meet the welding quality requirements and pipe manufacturing grade will be heavy work.

The multi-head production potential ratio increases the quantities of engineering management and quality supervision. For several straight seam pipe rolling units and corresponding welding equipment, the differences in the operation skills, quality awareness, distribution points, and control procedures of their operators will bring many difficulties in production management, schedule, inspection and acceptance, delivery coordination, and so on, which is very easy to cause confusion in management and coordination and quality prevarication between the manufacturer and the construction unit.

◆ quality assurance

According to the production standard of spiral welded pipe, the main inspection/control items of SSAW include:

Overall dimensions: outer diameter, wall thickness, ovality, curvature, perpendicularity of pipe end

Length and appearance quality: weld reinforcement, misalignment, steel pipe surface, delamination, inclusion, and weld defect judgment

chemical composition

Tensile test of welded joint

Hydrostatic test

Acid etching test

Nondestructive testing

Generally, spiral welded pipe units adopt online continuous inspection to ensure the welding quality of welds, which is another important feature that distinguishes spiral welded pipe production from straight welded pipe production. Continuous inspection is conducive to the monitoring of welding defects, the stability of welding quality, and the guarantee of welding grade.

Due to the limitation of the production process, it is very difficult to realize continuous inspection of longitudinal welded pipe. This will increase the probability of welding hidden dangers and quality problems, and even affect the overall working reliability of pipeline operations in the future.

◆ production qualification

The spiral welded pipe manufacturer shall hold the industrial product production license issued by the state. The license system requires that the manufacturer of spiral welded pipe shall first pass the review and assessment of the authoritative verification organization recognized by the state, have the corresponding production means and inspection equipment, the quality assurance system operates well and effectively, and the products shall meet the requirements of the grade and quality specifications of the national standards. The license shall be issued after being confirmed by the national industrial product production license office. Therefore, spiral welded pipe manufacturers have relatively perfect quality assurance systems and quality control operation procedures.

6. Development direction of SSAW steel pipe

Due to the increased bearing pressure of the pipeline, the increasingly harsh service conditions and the need to prolong the service life of the pipeline, the main development direction of spiral welded pipe is:

◆ produce large diameter thick wall pipe to improve pressure resistance;

◆ design and produce steel pipes with a new structure, such as double-layer spiral welded pipe, that is, the steel strip with a thickness of half of the pipe wall is welded into the double-layer pipe, which not only has higher strength than the single-layer pipe with the same thickness but also will not have brittle failure;

◆ develop new steel grades, improve the technical level of the smelting process, and widely adopt controlled rolling and post rolling waste heat treatment process to continuously improve the strength, toughness, and welding performance of pipe body;

◆ vigorously develop coated pipes. If anti-corrosion coating is applied on the inner wall of the pipe, it 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.

Spiral welded pipe plays an important role in gas transportation. With the planning and construction of a number of major pipeline projects at home and abroad, high value-added products such as large deformation pipeline steel, high-strength hot bends, and thick low-temperature pipe fittings show good market competitiveness and large market demand, while domestic enterprises have made slow progress in developing this series of products, High value-added and large deformation pipeline steel, hot bend steel, low-temperature pipe fitting steel for pipeline station, X100 straight seam submerged arc welded pipe, spiral seam submerged arc welded pipe and hot bend spiral welded pipe suitable for industrial application should be developed as soon as possible.