1. Uses: Seamless steel pipe is a kind of economical cross-section steel, which plays a very important role in the national economy. It is widely used in petroleum, chemical industry, boiler, power station, ship, machinery manufacturing, automobile, aviation, aerospace, energy, geology, construction and Various departments such as the military industry.
2. Classification
①According to the cross-section shape: circular cross-section pipe, special-shaped cross-section pipe
②According to the material: carbon steel pipe, alloy steel pipe, stainless steel pipe, composite pipe
③According to the connection method: threaded connection pipe, welded pipe
④According to the production method: hot-rolled (extruded, topped, expanded) tubes, cold-rolled (drawn) tubes
⑤According to usage: boiler tube, oil well tube, pipeline tube, structural tube, fertilizer tube ...
3. Production processes
①Main production process of hot-rolled seamless steel pipe (△Main inspection process):
Tube blank preparation and inspection△→tube blank heating→piercing→pipe rolling→barren tube reheating→diameter setting (reduction)→heat treatment△→finished tube straightening→finishing→inspection△(non-destructive, physical and chemical, Taiwan inspection)→input library
②Main production process of cold-rolled (drawn) seamless steel pipe:
Billet preparation→pickling and lubrication→cold rolling (drawing)→heat treatment→straightening→finishing→inspection
4. Quality requirements
①Chemical composition of steel: The chemical composition of steel is one of the most important factors affecting the performance of seamless steel pipes, and it is also the main basis for formulating the parameters of rolling process and heat treatment of steel pipes.
a. Alloying elements: intentionally added, according to the application
b. Residual elements: brought in by steelmaking, properly controlled
c. Harmful elements: strictly controlled (As, Sn, Sb, Bi, Pb), gases (N, H, O)
Refining outside the furnace or electroslag remelting: improve the uniformity of the chemical composition in the steel and the purity of the steel, reduce the non-metallic inclusions in the tube blank and improve their distribution.
② Steel pipe geometric dimension accuracy and shape
a. Steel pipe outer diameter accuracy: depends on the method of sizing (reducing) diameter, equipment operation, process system, etc.
Permissible deviation of outer diameter δ=(D-Di)/Di ×100% D: Maximum or minimum outer diameter mm
Di: nominal outer diameter mm
b. Steel pipe wall thickness accuracy: It is related to the heating quality of the tube blank, the process design parameters and adjustment parameters of each deformation process, the tool quality and its lubrication quality, etc.
Allowable deviation of wall thickness: ρ=(S-Si)/Si×100% S: maximum or minimum wall thickness on the cross section
Si: nominal wall thickness mm
C． Steel pipe ovality: indicates the degree of out-of-roundness of the steel pipe.
d. Steel pipe length: normal length, fixed (double) ruler length, length tolerance
e. Bending degree of steel pipe: indicates the radius of the steel pipe: the bending degree per meter of steel pipe length, the bending degree of the entire length of the steel pipe
f. Cutting slope of steel pipe end face: indicates the degree of inclination between the end face of steel pipe and the cross section of steel pipe
g. Steel pipe end bevel angle and blunt edge
5. Steel pipe surface quality: surface smooth requirements
a. Dangerous defects: cracks, inward folds, outward folds, crushed, separated layers, scars, concaves, convex hulls, etc.
b. General defects: pockmarks, green lines, scratches, bruises, slight inner and outer straights, roller marks, etc.
cause:
① Due to the surface defects or internal defects of the tube blank.
② Produced during the production process, such as incorrect design of rolling process parameters, rough mold surface, poor lubrication conditions, unreasonable pass design and adjustment.
③ During the heating and rolling, heat treatment and straightening process of the tube blank (steel pipe), if excessive residual stress is generated due to improper heating temperature control, uneven deformation, unreasonable heating and cooling speed or too large straightening deformation, then It may also cause surface cracks in the steel pipe.
6. Steel management properties: normal temperature mechanical properties, high temperature mechanical properties, low temperature properties, corrosion resistance. The physical and chemical properties of the steel pipe mainly depend on the chemical composition of the steel, the structure and the purity of the steel, and the heat treatment method of the steel pipe.
7. Process performance of steel pipe: flattening, flaring, curling, bending, welding, etc.
8. Metallographic structure of steel pipe: low-magnification structure (macro), high-magnification structure (micro) M, B, P, F, A, S
9. Special requirements for steel pipes: contract appendices, technical agreements.
(2) Quality inspection methods for seamless steel pipes:
1. Chemical composition analysis: chemical analysis, instrumental analysis (infrared CS instrument, direct reading spectrometer, zcP, etc.).
① Infrared C-S instrument: analyze ferroalloys, steelmaking raw materials, and C and S elements in steel.
② Direct reading spectrometer: C, Si, Mn, P, S, Cr, Mo, Ni, Cn, Al, W, V, Ti, B, Nb, As, Sn, Sb, Pb, Bi in bulk samples
③N-0 instrument: gas content analysis N, O
2. Steel pipe geometry and shape inspection:
① Steel pipe wall thickness inspection: micrometer, ultrasonic thickness gauge, no less than 8 points at both ends and record.
②Steel pipe outer diameter and ovality inspection: calliper gauge, vernier caliper, ring gauge, measure the maximum point and minimum point.
③ Steel pipe length inspection: steel tape, manual, automatic length measurement.
④Steel tube bending inspection: Ruler, level ruler (1m), feeler gauge, and thin line to measure bending degree per meter and full length bending degree.
⑤ Steel pipe end bevel angle and blunt edge inspection: angle ruler, clamping plate.
3. Steel pipe surface quality inspection: 100%
①Manual visual inspection: lighting conditions, standards, experience, signs, steel pipe rotation.
②Non-destructive testing inspection:
a. Ultrasonic flaw detection UT:
It is sensitive to surface and internal crack defects of various materials with uniform materials.
Standard: GB/T 5777-1996 Level: C5
b. Eddy current flaw detection ET: (electromagnetic induction)
Mainly sensitive to point (hole-shaped) defects. Standard: GB/T 7735-2004
Level: B level
c. Magnetic particle MT and magnetic flux leakage testing:
Magnetic flaw detection is suitable for the detection of surface and near-surface defects of ferromagnetic materials.
Standard: GB/T 12606-1999 Level: C4
d. Electromagnetic ultrasonic flaw detection:
No coupling medium is required, and it can be applied to high-temperature, high-speed, and rough surface flaw detection of steel pipes.
e. Penetration testing:
Fluorescence, coloring, and detection of steel pipe surface defects.
4. Steel management performance inspection:
① Tensile test: measure stress and deformation, determine the strength (YS, TS) and plasticity index (A, Z) of the material
Longitudinal and transverse specimen pipe section, arc, circular specimen (￠10,￠12.5)
Small bore, thin wall Large bore, thick wall Calibrated distance.
Note: The elongation of the sample after breaking is related to the size of the sample GB/T 1760
②Impact test: CVN, notch C type, V type, power J value J/cm2
Standard sample 10×10×55 (mm) Non-standard sample 5×10×55 (mm)
③Hardness test: Brinell hardness HB, Rockwell hardness HRC, Vickers hardness HV, etc.
④Hydraulic test: test pressure, pressure stabilization time, p=2Sδ/D
5. Steel pipe process performance inspection:
① Flattening test: round sample C-shaped sample (S/D>0.15) H=(1+2)S/(∝+S/D)
L=40～100mm Deformation coefficient per unit length=0.07～0.08
② Ring pull test: L=15mm, no crack is qualified
③ Flaring and crimping test: the top center taper is 30°, 40°, 60°
④ Bending test: can replace the flattening test (for large-diameter pipes)
6. Steel pipe metallographic analysis:
① High magnification inspection (microscopic analysis): non-metallic inclusions 100x GB/T 10561 grain size: grade, grade difference
Organization: M, B, S, T, P, F, A-S
Decarburized layer: inner and outer
Method A rating: Class A - sulfide B - oxide C - silicate D - spherical oxidation DS
②Low magnification test (macroscopic analysis): below 10x with the naked eye and a magnifying glass
a. Acid etching test method, b. Sulfur print test method (tube billet test, showing low culture tissue and defects, such as looseness, segregation, subcutaneous air bubbles, skin turning, white spots, inclusions, etc.
c. Tower-shaped hairline test method: test the number, length and distribution of hairlines.
(3) my country's current seamless steel pipe standards:
1. Current seamless steel pipe standards: a total of 47 items, including: GB 25 items, HB 3 items, special purpose 19 items; basic 2 items, product 45 items
2. Commonly used standards: ① GB/T 2102-2006 Inspection, packaging, marking and quality certificate of steel pipes.
② GB/T 17395-1998 seamless steel pipe size, shape, weight and allowable deviation.
③ GB 5310-1995 Seamless steel tubes for high pressure boilers.
④ GB 6479-2000 Seamless steel tubes for high-pressure fertilizer equipment.
⑤ GB/T 18248-2000 seamless steel tubes for gas cylinders.
