The seamless steel pipe is a steel pipe made of a single piece of metal with no joints on the surface, called a seamless steel pipe. According to the production method, the seamless pipe is divided into a hot rolled pipe, a cold rolled pipe, a cold drawn pipe, an extruded pipe, a top pipe, and the like. According to the shape of the section, the seamless steel tube is divided into two types: a circular shape and a special shape. The shaped tube has a plurality of complicated shapes such as a square shape, an elliptical shape, a triangular shape, a hexagonal shape, a melon shape, a star shape, and a winged tube. The maximum diameter is 650mm and the minimum diameter is 0.3mm. Depending on the application, there are thick-walled tubes and thin-walled tubes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemicals, boiler tubes, bearing tubes, and high-precision structural steel tubes for automobiles, tractors, and aviation.
Use of seamless steel pipe
Seamless steel tubes are used in a wide range of applications. 
1. The general-purpose seamless steel pipe is rolled from ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, and has the largest output, and is mainly used as a pipe or structural component for conveying fluid. .
2. According to the use of three types of supply: a, according to chemical composition and mechanical properties; b, according to mechanical properties; c, according to water pressure test supply. Steel pipes supplied in categories a and b, if used to withstand liquid pressure, are also subjected to hydrostatic testing. 
3. Special-purpose seamless pipes include boiler seamless pipes, chemical power, geological seamless steel pipes and petroleum seamless pipes.
Seamless steel tubes have hollow sections and are used in large quantities as pipelines for transporting fluids, such as pipelines for transporting petroleum, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, the steel pipe has a lighter weight when it has the same bending and torsional strength, and is an economical section steel.
Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automotive drive shafts, bicycle frames and steel scaffolding used in construction, such as steel scaffolding, to make ring parts, improve material utilization, simplify manufacturing processes, save materials and processing In working hours, steel pipes have been widely used for manufacturing.
Seamless steel pipe quality requirements in production
1. Chemical composition
In order to improve the uniformity of chemical composition and the purity of steel, reduce the non-metallic inclusions of the tube and improve its distribution, often use the furnace refining equipment for the molten steel Refining, and even the use of electroslag furnace on the tube for remelting refining.
2. Dimensional accuracy and shape
The geometrical dimensions of the seamless steel pipe mainly include the outer diameter of the steel pipe, the wall thickness, the ellipticity, the length, the curvature, the cutting angle of the pipe end, the angle of the groove and the cross section of the blunt edge and the opposite.
3. The surface quality
The standard specifies the “smooth surface” requirements of seamless steel tubes. Common defects are: cracks, hairlines, inside the fold, outside the fold, rolling, within the straight, outside the straight, from the layer, scarring, pits, convex package, Ma Hang (Ma face), scratches (scratches) , Internal spiral, outer spiral, green line, concave, roll and so on. Which is broken, broken, broken, rolling, from the layer, scarring, pits, convex hull and other dangerous defects; steel plum, green line, abrasions, slightly inside and outside the straight, slightly inside and outside the spiral, Concave, roll for the general defects.
4. Physical and chemical properties
Including the mechanical properties at room temperature and mechanical properties at a certain temperature (thermal and low temperature performance) and corrosion resistance (such as oxidation, anti-acid, anti-acid and other properties) under normal circumstances depends on the chemical composition of steel, The organizational properties and the purity of the steel and the heat treatment of steel. In some cases, the rolling temperature and deformation of the steel pipe will also have an impact on the performance of the pipe.
Production process of seamless steel pipe
Tube blank preparation and inspection △→Tube heating→Perforation→Rolling tube→Steel tube reheating→Fixed (reduced) diameter→heat treatment △→finished tube straightening→finishing→inspection △(non-destructive, physicochemical, Taiwan inspection)→WarehousingHot-rolled seamless steel pipe production base deformation process can be summarized as three stages: perforation, extension and finishing.
a. Inner surface defects
1. An inner flap: presenting a straight line, a spiral or a semi-helical sawtooth defect on the inner surface of the steel pipe.
2. inside scarring: scars in the steel pipe inner surface, generally easily peel off. 
3. Warping: a straight line or intermittent small nail-like tilt leather. Often seen in the capillary head, and easy to peel. 
4. inside straights: a straight shape scratch with a certain width and depth. 
5. inner edge: a straight shape protrusion with a certain width and depth. 
6. inner drum kits: a super and regular protrusion and outer surface is not damaged. 
7. Pull pits: a regular or non-regular pit and the outer surface without damage. 
8. internal thread (this defect produced only at Accel units): spiral traces often seen in the thin-walled tube surface, and there are obvious rugged feelings.
b. outer surface defects
1. An outer fold: the outer surface of the pipe presents a layered folded spiral. 
2. separation: presenting a spiral shape or blocky delamination and cracking. 
3. external scarring: scars on the outer surface. 
4. pock surface: steel surface showed uneven pits. 
5. Line: a substantially symmetrical or asymmetrical linear rolling marks. 
6. Hairline: a continuous or discontinuous hairy fine lines. 
7. net cracks: scaly small cracks. 
8. scratches: linear or spiral-shaped groove-like defects. 
9. touch deflated: the outer surface of the steel pipe rendered in a convex outer concave phenomenon, and pipe wall thickness without injury. 
10. bumps: collision irregular scars. 
11. straightening recess: steel spiral concave outer surface. 
12. rolled off: longitudinally local or long presentation in a convex outer concave folds, the outer surface into strips depression. 
13. crack:opened the rupture surface phenomenon, much produced in the thin-walled tube.