I. Definition of seamless pipe:
Seamless steel pipes are made by piercing a whole round steel bar. Steel pipes without weld seams on the surface are called seamless steel pipes.
According to the production method, seamless pipes can be classified into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and pipe jacking, etc.
According to the cross-sectional shape, seamless pipes are divided into two types: round and special-shaped. Special-shaped pipes come in various complex shapes such as square, oval, triangular, hexagonal, melon seed-shaped, star-shaped, and finned pipes. The maximum diameter reaches 900mm and the minimum diameter is 4mm.
According to different uses, there are thick-walled seamless pipes and thin-walled seamless pipes.
Seamless steel pipes are mainly used as oil geological drilling pipes, cracking pipes for petrochemicals, boiler pipes, bearing pipes, as well as high-precision structural steel pipes for automobiles, tractors and aviation.
II. Execution standards for seamless pipes:
(1) Domestic implementation standard:
GB/T 17395-2024: It stipulates the dimensions, shapes, weights and allowable deviations of seamless tubes, etc.
GB/T 8162-2018: Applicable to seamless steel tubes for fluid conveyance, it stipulates their technical requirements, inspection methods, etc.
GB/T 8163-2018: Applicable to seamless steel tubes for fluid transportation, it stipulates the material, specification, performance, etc. of the steel tubes.
GB/T 3091-2015: It is applicable to welded steel pipes for low-pressure fluid transportation. Although it mainly targets welded steel pipes, some technical indicators can also be used as references for seamless steel pipes.
GB/T 13296-2013: Applicable to seamless steel tubes for boilers and heat exchangers, it stipulates their technical requirements, test methods, etc.
(2) International implementation standard:
ISO 1127-2021: The standard for seamless steel pipes formulated by the International Organization for Standardization, which stipulates the requirements for the dimensions, tolerances, mechanical properties, etc. of steel pipes.
ASTM A53/A53M-2021: American Society for Testing and Materials standard, applicable to welded and seamless steel pipes, specifying their chemical composition, mechanical properties, dimensional tolerances, etc.
EN 10305-2022: European standard, applicable to seamless steel tubes, specifying their dimensions, tolerances, mechanical properties, etc.
JIS G 3444-2020: Japanese Industrial standard, applicable to seamless steel pipes for common structures, stipulating their technical requirements, inspection methods, etc
III. Seamless pipe production process:
Seamless pipes can be classified into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, extruded pipes, jacking pipes, etc. according to their production processes. The following are their production processes:
(1) Hot-rolled pipe
Raw material preparation: Solid round steel billets or ingots should be used. Surface defects should be inspected and the required lengths should be cut.
Heating and piercing: Heat the steel billet to 1200-1300℃, and form hollow rough tubes through the action of the rotating head of the piercing machine and the rolls.
Rolling and sizing: The rough tubes are rolled multiple times in a hot rolling mill to reduce the wall thickness, then the uniformity of the wall thickness is adjusted by a sizing machine, and finally the outer diameter size is determined by a sizing machine.
Subsequent processing: After cooling, straightening, hydrostatic testing (or flaw detection), marking, and finally storage.
(2) Cold-rolled pipe
Billet preparation: Acid wash and lubricate the tube billet.
Cold rolling: It is carried out on a two-roll mill, using a ring-shaped die and a conical head for rolling. It is suitable for products with high precision and high surface quality requirements.
Subsequent processing: After cold rolling, the steel pipes need to undergo heat treatment, straightening, finishing, inspection and other procedures.
(3) Cold-drawn tube
Billet preparation: Acid wash and lubricate the tube billet.
Cold drawing: At room temperature, steel pipes are drawn through dies, gradually reducing the outer diameter and wall thickness. The drawing speed and reduction rate need to be controlled to prevent cracks.
Subsequent processing: The cold-drawn steel pipes need to undergo heat treatment, straightening, finishing, inspection and other procedures.
(4) Extruded tube
Billet preparation: Perforate or expand the peeled round billet.
Extrusion: The heated tube blank is placed in a closed extrusion cylinder. Through the cooperation of the piercing rod and the extrusion rod, the material is extruded from the die hole, which is suitable for the production of small-diameter steel pipes.
Subsequent processing: The extruded steel pipes need to undergo heat treatment, straightening, finishing, inspection and other procedures.
(5) Pipe jacking
Billet preparation: Heat the tube billet to a certain temperature.
Pipe jacking: The pipe blank is jacked into steel pipe by a pipe jacking machine.
Subsequent processing: The steel pipes after jacking need to undergo heat treatment, straightening, finishing, inspection and other procedures.
IV. Material classification and properties of seamless pipes:
(1) Material classification
Common carbon structural steels: such as Q215-A to Q275-A, with moderate strength and low cost, are used for general fluid transportation and structural components.
High-quality carbon structural steel: Such as steel grades 10 to 50, has excellent mechanical properties and is used to manufacture mechanical parts with high requirements.
Low alloy steels: Such as 09MnV, 16Mn, etc., have high strength and good toughness, and are suitable for high-pressure fluid transportation.
Alloy steel: It contains multiple alloying elements, has high strength and hardness, and is used for mechanical parts that bear high loads and harsh environments.
Stainless steel: such as 904L, etc., has good corrosion resistance and is suitable for the chemical, food, pharmaceutical and other industries.
(2) Performance
Strength: Strength varies with different materials. Alloy steel and low alloy steel have higher strength.
Toughness: High-quality carbon structural steel and low alloy steel have good toughness and can resist impact.
Corrosion resistance: Stainless steel seamless pipes have excellent corrosion resistance and can resist the erosion of various chemical media.
Processing performance: Common carbon structural steel and high-quality carbon structural steel have better processing performance and are easy to weld, cut and form.
Surface quality: The inner and outer surfaces are smooth, which can reduce fluid resistance.
V. The production process flow of seamless pipes:
Raw material preparation: Select appropriate steel billets or tube billets and carry out surface cleaning (such as pickling, sandblasting, etc.) to remove impurities.
Heating: Heat the steel billet to 1100℃ – 1300℃ to ensure uniform temperature.
Piercing: Solid steel billets are pierced into hollow rough tubes through a piercing machine.
Rolling: The rough tubes undergo multiple passes on a hot rolling mill, gradually reducing the outer diameter and wall thickness while adjusting the uniformity of the wall thickness.
Sizing: The final outer diameter of the steel pipe after hot rolling is determined by a sizing machine.
Cooling: After the steel pipes are cooled, they are straightened to ensure straightness.
Subsequent processing: including hydrostatic testing (or flaw detection), marking, inspection, etc. After passing, it will be stored in the warehouse.
VI. Application fields of seamless pipes:
Petroleum and natural gas: It is used for transporting fluids such as petroleum and natural gas, and for making oil pipes, gas pipes and drill pipes, etc.
Chemical industry: Transporting corrosive media, manufacturing equipment such as reaction vessels and heat exchangers.
Mechanical manufacturing: Manufacturing mechanical parts, shafts, hydraulic cylinders, etc.
Architecture and Structure: Used for building structural components, Bridges, towers, etc.
Automobile manufacturing: Used in components such as automobile chassis, drive shafts, exhaust pipes, etc.
Shipbuilding: Structural components, piping systems, etc. used in ships.
Food and pharmaceuticals: Stainless steel seamless tubes are used in food processing and pharmaceutical equipment to ensure hygiene and corrosion resistance.
Power industry: Piping systems for equipment such as boilers and steam turbines.
Aerospace: Used for manufacturing high-strength and lightweight aviation components.
Others: such as medical devices, sports equipment, decoration and other fields.
VII. A brief description of different types of seamless pipes and their applicable fields:
i. Ordinary carbon structural steel seamless pipe
Features: Moderate strength, low cost, and good processing performance.
Application fields: General-purpose fluid transportation pipelines (such as water and air), building structural components, common mechanical parts, etc.
ii. High-quality carbon structural steel seamless pipe
Characteristics: Good mechanical properties, high strength and toughness.
Application fields: Mechanical parts with high requirements (such as shafts and connecting rods), medium and low pressure fluid conveying pipelines.
iii. Low alloy steel seamless pipe
Features: High strength, good toughness, and improved corrosion resistance compared to ordinary carbon steel.
Application fields: High-pressure fluid conveying pipelines (such as oil and natural gas), bridge structural components, high-pressure boiler pipelines.
iv. Alloy steel seamless pipe
Features: High strength, high hardness, high temperature resistance and wear resistance.
Application fields: High-temperature and high-pressure equipment (such as power station boilers), mining machinery (such as hydraulic supports), aerospace components.
v. Stainless steel seamless pipe
Features: Strong corrosion resistance, good hygiene performance, and smooth surface.
Application fields: Corrosive medium transportation in the chemical industry, food processing equipment, pharmaceutical equipment, medical devices, decoration fields.
vi. Special-purpose seamless tubes
Features: Customized according to specific requirements, such as high strength, high toughness, high temperature resistance, wear resistance, etc.
Application fields: Automotive manufacturing (such as exhaust pipes, drive shafts), shipbuilding (such as seawater pipelines), aerospace (such as high-strength structural components), etc.
VIII. Shipment in seamless pipe packaging
Packaging
Bundled packaging
The same bundle of steel pipes should be of the same furnace number, steel grade and specification, and should not be bundled in the same furnace (batch number).
The weight of each bundle of steel pipes generally does not exceed 3,000 kilograms. With the user’s consent, it can be increased to 5,000 kilograms.
When bundling flat-end steel pipes, one end should be aligned, and the difference between the ends of the aligned pipes should be less than 20mm.
When bundling steel pipes with couplings, the couplings of the two adjacent rows of steel pipes at the top and bottom should be arranged alternately front and back.
Container packaging
Cold-rolled or cold-drawn seamless steel pipes and surface-polished hot-rolled stainless steel pipes can be packaged in containers (such as iron boxes and wooden boxes).
The weight of the packaged containers should comply with relevant regulations. For example, for steel pipes with an outer diameter of 20mm or more, the maximum weight of each container is 2000kg.
The inner walls of the container should be lined with moisture-proof materials such as felt paper or plastic sheeting, and an appropriate amount of desiccant should be added.
Special packaging:
Stainless steel mirror-finished tubes and precision tubes are usually elaborately packaged. Each steel pipe is wrapped in a special plastic bag, placed in a wooden box, and tied with stainless steel straps.
The stainless steel pipes for foreign trade export should be wrapped with an additional layer of moisture-proof and fireproof non-woven fabric on the outside of the packaging.
Shipment
Mode of transportation:
Long-distance transportation usually adopts 20-foot or 40-foot containers.
Steel pipes in the cabin should be properly padded and supported to prevent the pipes from rolling due to the tilting of the hull.
Loading requirements:
When loading, disk hoists, nylon belts or steel wire ropes with protective isolation devices should be used for hoisting to avoid damaging the pipe body.
When hoisting bundled steel pipes, it is not allowed to lift more than two bundles simultaneously. If the weight of a single bundle exceeds 3,000 kilograms, only single bundle hoisting is permitted.
Storage and Protection
Steel pipes that have undergone cold rolling, cold drawing or bright annealing are not allowed to be stored outdoors. If outdoor storage is necessary, protective measures should be taken.
Steel pipes should be placed with sleepers in the carriage to prevent being pricked.
Through these packaging and shipping processes, seamless pipes can be effectively protected from damage during transportation, ensuring product quality and performance.
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