Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard was proposed by China Iron and Steel Association.
This standard is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183).
Contens
Foreword I
1 Scope 1
2 Normative reference 1
3 Classification and code 3
4 Order contents 3
5 Dimension, shape, weight and tolerance 4
6 Technical requirements 8
7 Test method 12
8 Inspection rules 13
9 Packaging, marking and quality certificate 14
Cold-drawn or cold-rolled precision inside diameter seamless
steel tubes for hydraulic and pneumatic system service
1 Scope
This standard specifies the classification and code, ordering content, dimension, shape, weight, tolerance, technical requirements, test methods, inspection rules, packaging, marking and product quality certificates for hydraulic and pneumatic system service.
This standard is applicable to the cold-drawn or cold-rolled precision inside diameter seamless steel tubes for hydraulic and pneumatic system service (hereinafter referred to as steel tubes).
2 Normative reference
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 222 Permissible tolerances for chemical composition of steel products
GB/T 223.5 Steel and iron — Determination of acid-soluble silicon and total silicon content — Reduced molybdosilicate spectrophotometric method
GB/T 223.12 Methods for chemical analysis of iron, steel and alloy — The sodium carbonate separation-diphenyl carbazide photometric method for the determination of chromium content
GB/T 223.23 Iron, steel and alloy — Determination of nickel content — The dimethylglyoxime spectrophotometric method
GB/T 223.26 Iron, steel and alloy — Determination of molybdenum content — The thiocyanate spectrophotometric method
GB/T 223.53 Methods for chemical analysis of iron, steel and alloy — Flame atomic absorption spectrometric method for the determination of copper content
GB/T 223.59 Iron, steel and alloy — Determination of phosphorus content — Bismuth phosphomolybdate blue spectrophotometric method and antimony phosphomolybdate blue spectrophotometric method
GB/T 223.63 Methods for chemical analysis of iron, steel and alloy — The sodium (potassium) periodate photometric method for the determination of manganese content
GB/T 223.68 Methods for chemical analysis of iron, steel and alloy — The potassium iodate titration method after combustion in the pipe furnace for the determination of sulfur content
GB/T 223.69 Iron, steel and alloy — Determination of carbon contents — Gas-volumetric method after combustion in the pipe furnace
GB/T 228.1 Metallic materials — Tensile testing — Part 1: Method of test at room temperature
GB/T 229 Metallic materials — Charpy pendulum impact test method
GB/T 242 Metallic materials — Tube — Drift expanding test
GB/T 246 Metallic materials — Tube — Flattening test
GB/T 699-2015 Quality carbon structure steels
GB/T 1031 Geometrical product specifications (GPS) — Surface texture: Profile method — Surface roughness parameters and their values
GB/T 1591-2008 High strength low alloy structural steels
GB/T 2102 Acceptance, packing, marking and quality certification of steel pipe
GB/T 2975 Steel and steel products — Location and preparation of samples and test pieces for mechanical testing
GB/T 3077-2015 Alloy structure steels
GB/T 4336 Carbon and low-alloy steel — Spark discharge atomic emission spectrometric method (routine method)
GB/T 6394 Determination of estimating the average grain size of metal
GB/T 7735-2004 Steel tubes — The inspection method on eddy current test
GB/T 12606-2016 Automated full peripheral flux leakage testing of seamless and welded (except submerged arc-welded) ferromagnetic steel tubes for the detection of longitudinal and/or transverse imperfections
GB/T 17395 Dimensions, shapes, masses and tolerances of seamless steel tubes
GB/T 20066 Steel and iron — Sampling and preparation of samples for the determination of chemical composition
GB/T 20123 Steel and iron — Determination of total carbon and sulfur content — Infrared absorption method after combustion in an induction furnace (routine method)
GB/T 20125 Low-alloy steel — Determination of multi-element contents — Inductively coupled plasma atomic emission spectrometric method
3 Classification and code
Steel tubes are classified and coded according to delivery state as follows:
a) Cold-drawn or cold-rolled/hard: +C;
b) Cold-drawn or cold-rolled/soft: +LC;
c) Stress-relief annealing after cold-drawn or cold-rolled: +SR;
d) Annealing: +A;
e) Normalizing: +N.
4 Order contents
The contract or order for ordering steel tubes according to this standard shall include but not be limited to the following contents:
a) Standard No.;
b) Product name;
c) Steel designation (quality grade);
d) Dimension and specification;
e) The order quantity (total weight or total length);
f) Delivery state;
g) Manufacturing method;
h) Special requirements.
5 Dimension, shape, weight and tolerance
5.1 Dimension
5.1.1 Steel tubes are usually delivered with inner diameter and wall thickness. If the purchaser requires outer diameter and inner diameter or outer diameter and wall thickness for delivery, it shall be indicated in the contract.
5.1.2 For the inner diameter and wall thickness of steel tubes, the dimensions listed in Table 1 shall be prior. Steel tubes with specifications other than those given in Table 1 may be supplied upon agreement between the supplier and the purchaser.
5.1.3 The tolerances for the inner and outer diameter of cold working (+C, +LC) steel tubes shall meet those specified in Table 1 and Table 2. For the steel tubes in thermal treatment (+SR, +A and +N) status, their tolerances for the inner and outer diameter shall meet those specified in Table 3.
5.1.4 As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, steel tubes beyond the tolerances specified in Tables 1, 2 and 3 may be supplied.
Foreword I
1 Scope
2 Normative reference
3 Classification and code
4 Order contents
5 Dimension, shape, weight and tolerance
6 Technical requirements
7 Test method
8 Inspection rules
9 Packaging, marking and quality certificate
ICS 77.140.75
H 48
National Standard of the People’s Republic of China
GB/T 32957-2016
Cold-drawn or cold-rolled precision inside diameter seamless
steel tubes for hydraulic and pneumatic system service
液壓和氣動系統(tǒng)設(shè)備用冷拔或冷軋
精密內(nèi)徑無縫鋼管
Issue date: 2016-08-29 Implementation date: 2017-07-01
the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Issued by
?
Foreword
This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard was proposed by China Iron and Steel Association.
This standard is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183).
?
Cold-drawn or cold-rolled precision inside diameter seamless
steel tubes for hydraulic and pneumatic system service
1 Scope
This standard specifies the classification and code, ordering content, dimension, shape, weight, tolerance, technical requirements, test methods, inspection rules, packaging, marking and product quality certificates for hydraulic and pneumatic system service.
This standard is applicable to the cold-drawn or cold-rolled precision inside diameter seamless steel tubes for hydraulic and pneumatic system service (hereinafter referred to as steel tubes).
2 Normative reference
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 222 Permissible tolerances for chemical composition of steel products
GB/T 223.5 Steel and iron — Determination of acid-soluble silicon and total silicon content — Reduced molybdosilicate spectrophotometric method
GB/T 223.12 Methods for chemical analysis of iron, steel and alloy — The sodium carbonate separation-diphenyl carbazide photometric method for the determination of chromium content
GB/T 223.23 Iron, steel and alloy — Determination of nickel content — The dimethylglyoxime spectrophotometric method
GB/T 223.26 Iron,steel and alloy — Determination of molybdenum content — The thiocyanate spectrophotometric method
GB/T 223.53 Methods for chemical analysis of iron, steel and alloy — Flame atomic absorption spectrometric method for the determination of copper content
GB/T 223.59 Iron, steel and alloy — Determination of phosphorus content — Bismuth phosphomolybdate blue spectrophotometric method and antimony phosphomolybdate blue spectrophotometric method
GB/T 223.63 Methods for chemical analysis of iron, steel and alloy — The sodium (potassium) periodate photometric method for the determination of manganese content
GB/T 223.68 Methods for chemical analysis of iron, steel and alloy — The potassium iodate titration method after combustion in the pipe furnace for the determination of sulfur content
GB/T 223.69 Iron, steel and alloy — Determination of carbon contents — Gas-volumetric method after combustion in the pipe furnace
GB/T 228.1 Metallic materials — Tensile testing — Part 1: Method of test at room temperature
GB/T 229 Metallic materials — Charpy pendulum impact test method
GB/T 242 Metallic materials — Tube — Drift expanding test
GB/T 246 Metallic materials — Tube — Flattening test
GB/T 699-2015 Quality carbon structure steels
GB/T 1031 Geometrical product specifications (GPS) — Surface texture: Profile method — Surface roughness parameters and their valuesGeometrical product specifications (GPS) — Surface texture: Profile method — Surface roughness parameters and their values
GB/T 1591-2008 High strength low alloy structural steels
GB/T 2102 Acceptance, packing, marking and quality certification of steel pipe
GB/T 2975 Steel and steel products — Location and preparation of samples and test pieces for mechanical testing
GB/T 3077-2015 Alloy structure steelsAlloy structure steels
GB/T 4336 Carbon and low-alloy steel — Spark discharge atomic emission spectrometric method (routine method)
GB/T 6394 Determination of estimating the average grain size of metal
GB/T 7735-2004 Steel tubes — The inspection method on eddy current test
GB/T 12606-2016 Automated full peripheral flux leakage testing of seamless and welded (except submerged arc-welded) ferromagnetic steel tubes for the detection of longitudinal and/or transverse imperfections
GB/T 17395 Dimensions, shapes, masses and tolerances of seamless steel tubes
GB/T 20066 Steel and iron — Sampling and preparation of samples for the determination of chemical composition
GB/T 20123 Steel and iron — Determination of total carbon and sulfur content — Infrared absorption method after combustion in an induction furnace (routine method)
GB/T 20125 Low-alloy steel — Determination of multi-element contents — Inductively coupled plasma atomic emission spectrometric method
3 Classification and code
3.2 Steel tubes are classified and coded according to delivery state as follows:
a) Cold-drawn or cold-rolled/hard: +C;
b) Cold-drawn or cold-rolled/soft: +LC;
c) Stress-relief annealing after cold-drawingdrawn or cold-rollingrolled: +SR;
d) Annealing: +A;
e) Normalizing: +N.
4 Order contents
The contract or order for ordering steel tubes according to this standard shall include but not be limited to the following contents:
a) Standard No.;
b) Product name;
c) Steel designation (quality grade);
d) Dimension and specification;
e) The order quantity (total weight or total length);
f) Delivery state;
g) Manufacturing method;
h) Special requirements.
5 Dimension, shape, weight and tolerance
5.1 Dimension
5.1.1 Steel tubes are usually delivered with inner diameter and wall thickness. If the purchaser requires outer diameter and inner diameter or outer diameter and wall thickness for delivery, it shall be indicated in the contract.
5.1.2 For the inner diameter and wall thickness of steel tubes, the dimensions listed in Table 1 shall be prior. Steel tubes with specifications other than those given in Table 1 may be supplied upon agreement between the supplier and the purchaser.
5.1.3 The tolerances for the inner and outer diameter of cold working (+C, +LC) steel tubes shall meet those specified in Table 1 and Table 2. For the steel tubes in thermal treatment (+SR, +A and +N) status, their tolerances for the inner and outer diameter shall meet those specified in Table 3.
5.1.4 As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, steel tubes beyond the tolerances specified in Tables 1, 2 and 3 may be supplied.
Table 1 Inner diameter, wall thickness and the tolerances for inner diameter of steel tubes In: mm
Inner diameter Wall thickness
1.5 2.0 2.5 3.0 4.5 5.0 6.0 7.5 8.0 9.0 10 11 12 14 15 17 18 22 25 28 30 35 45
Tolerances for inner diameter
Table 2 Tolerances for outer diameter of cold working (+C, +LC) steel tubes In: mm
Inner diameter (dd) Wall thickness (SS) / outer diameter (dD) a Tolerances for outer diameter
25 ≤ d ≤ 180 SS/DD ≥ 0.05 ± 0.40
0.025 ≤ S/D < 0.05 ± 0.50
SS/DD < 0.025 ± 0.60
180 < d ≤ 320 SS/DD ≥ 0.05 ± 0.70
0.025 ≤ SS/DD < 0.05 ± 0.80
SS/DD < 0.025 ± 0.90
320 < d ≤ 500 SS/DD ≥ 0.05 ± 1.00
0.025 ≤ SS/DD < 0.05 ± 1.10
SS/DD < 0.025 ± 1.20
a When a steel tube is delivered with inner diameter and wall thickness, DD is the calculated outer diameter; When the steel tube is delivered with outer diameter and inner diameter, SS is the calculated wall thickness.
Table 3 Tolerances for outer diameter and inner diameter of steel tubes with thermal treatment (+SR, +A and +H) In: mm
Wall thickness (SS) / outer diameter (dD) a Tolerances
SS/DD ≥ 0.05 Values specified in Table 1 and Table 2
0.025 ≤ SS/DD < 0.05 1.2 times the value specified in Table 1 and Table 2
SS/DD < 0.025 1.5 times the value specified in Table 1 and Table 2
a When a steel pipe is delivered with inner diameter and wall thickness, DD is the calculated outer diameter; When the steel pipe is delivered with outer diameter and inner diameter, SS is the calculated wall thickness.
5.1.5 When a steel tube is delivered with inner diameter and wall thickness or outer diameter and wall thickness, the wall thickness shall meet the requirements specified in Table 4. 4.2.2 Steel tubes beyond the tolerances specified in Table 4 may be supplied upon the negotiation between the supplier and the purchaser.
Table 4 Tolerances for wall thickness of steel tubes In: mm
Steel tube wall thickness (S) 1.5 < S ≤ 7 7 < S ≤ 13.5 13.5 < S ≤ 20 S > 20
Tolerances ± 8％ S ± 7％ S ± 6.5％ S ± 6％ S
5.1.6 When steel tubes are delivered with outer diameter and inner diameter, the wall thickness shall not exceed 16% of the calculated wall thickness.
5.2 Length
5.2.1 Random length
The random length of steel tubes is 3,000 mm to 12,000 mm.
5.2.2 Cut and multiple lengths
5.2.2.1 As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, steel tubes may be delivered in cut length or multiple length.
5.2.2.2 The cut length and multiple length shall be within the random length. The tolerance for cut length shall meet the following requirements:
a) Where the length not greater than 5,000 mm, mm;
b) Where the length greater than 5,000 mm, mm.
5.2.2.3 The notch allowance shall be reserved for each multiple length according to following requirements:
a) a) When D ≤ 159 mm, 5 mm ~ 10 mm;
b) When D > 159 mm, 10 mm ~ 15 mm.
5.3 Curvature
5.3.1 The curvature of steel tubes shall meet the requirements of curvature per meter and curvature of full length at the same time. When the precision grade is not specified in the contract, the curvature shall be implemented according to Grade A.
5.3.2 The curvatures of steel tubes per meter are divided into the following three precision grades:
a) Grade A which is not greater than 1.0 mm/m;
b) Grade B which is not greater than 0.5 mm/m;
b) Grade BC which is not greater than 0.3 mm/m.
5.3.3 The full-length curvatures of steel tubes are divided into the following three precision grades:
a) a) Grade A which is not greater than 0.1% of the full length;
b) b) Grade B which is not greater than 0.05% of the full length;
c) Grade C which is not greater than 0.03% of the full length.
5.3.4 As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, other requirements of curvature per meter and curvature of full length may be adopted.
5.4 End shape
The surface of steel tube at both ends shall be vertical to steel tube axes and notch burrs shall be cleared away.
5.5 Out-of-roundness
When the steel tube is delivered with inner diameter and wall thickness, the out-of-roundness of the inner diameter of the steel tube shall not exceed 80% of the tolerance of the inner diameter. Measuring position of inner diameter shall meet the requirements in Table 5.
Table 5 Measuring position of the out-of-roundness of steel tube inner diameter In: mm
Wall thickness (S)/ outer diameter (D) Measuring position from the end (L)
S/D < 0.025 L ≥ 40% D, and L ≥ 50 mm
0.025 ≤ S/D < 0.05 L ≥ 30% D, and L ≥ 35 mm
S/D ≥ 0.05 L ≥ 20% D, and L ≥ 25 mm
5.6 Weight
The steel tubes may be delivered either in actual weight or in theoretical weight. The theoretical weight of steel tube per meter shall meet those specified in GB/T 17395, with the density of steel taken as 7.85 kg/dm3.
6 Technical requirements
6.1 Designation and chemical composition of steel
6.1.1 The designation and chemical composition (melting composition) of steel shall meet the requirements of 20, 45 and 25Mn in GB/T 699-2015, Q345B (C, D and E) in GB/T 1591-2008 and 27SiMn in GB/T 3077-2015 respectively.
6.1.2 If the chemical composition analysis is required by the purchaser, it shall be indicated in the contract. And the tolerances for chemical composition of finished steels shall meet the requirements of GB/T 222.
6.1.3 As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, the steelssteel tubes with other designation may be supplied.
6.2 Manufacturing method
6.2.1 Steel shall be smelted by the method of external refining with electric arc furnace or of external refining with oxygen converter, and shall be degassed in vacuum. As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, other smelting methods with higher-level requirements may be adopted. When the purchaser specifies a certain smelting method, it shall be indicated in the contract.
6.2.2 Steel tubes shall be manufactured with the cold-drawingdrawn or cold-rollingrolled method. When the purchaser specifies a certain manufacture method, it shall be indicated in the contract.
6.3 Delivery state
Steel tubes shall be delivered in one of the states listed in Table 6.
Table 6 Delivery state
Delivery state Code Remarks
Cold drawn/hard or cold rolled/hard +C No heat treatment after final cold working
Cold drawn/soft or cold rolled/soft +LC Proper cold working after final thermal treatment
Stress-relief annealing after cold-drawingdrawn or cold-rollingrolled +SR Stress-relief annealing shall be conducted in steel tube after final cold working
Annealing +A Complete annealing shall be conducted in steel tube after final cold working
Normalizing +N Normalizing shall be conducted in steel tube after final cold working
6.4 Mechanical properties
6.4.1 The longitudinal mechanical property of the steel tubes in delivery condition shall meet those specified in Table 7. The mechanical properties of the steel tubes with other designation shall be determined by the supplier and the purchaser through negotiation.
Table 7 Mechanical properties of steel tubes
Steel designation Delivery state a
+C b +LC b +SR A c+Ac +N Temperature of impact test
°C
Tensile strength
Rm
MPa Percentage elongation after fracture
AA
% Tensile strength
Rm
MPa Percentage elongation after fracture
AA
% Tensile strength
Rm
MPa Upper yield strength
ReH
MPa Percentage elongation after fracture
AA
% Absorbed energy of impact
KV2
J Tensile strength
Rm
MPa Percentage elongation after fracture
AA
% Absorbed energy of impact
KV2
J Tensile strength
Rm
MPa Upper yield strength
ReH
MPa Percentage elongation after fracture
AA
% Absorbed energy of impact
KV2
J
Not less than
20 550 5 520 8 480 375 10 — 390 21 — 410 255 21 — —
45 645 4 630 6 600 450 6 — 590 14 — 540 340 18 — —
27SiMn 750 4 700 6 650 520 8 — 600 10 — 650 430 14 — —
Q345B 680 8 650 10 600 450 12 15 450 22 27 490 355 22 34 20
Q345C 0
Q345D -20
Q345E -40
25Mn 650 6 620 8 560 430 10 12 430 20 27 460 300 20 27 Room temperature
a For the steel tubes with an outer diameter of not more than 30 mm and a wall thickness of not more than 3 mm, its minimum yield strength may be reduced by 10 MPa.
b The yield strength is very close to the tensile strength due to the degree of cold working deformation, therefore, the following relation is recommended for calculation:
— +C state: ReH ≥ 0.8 Rm;
— +LC state: ReH ≥ 0.7 Rm.
cc The following relation is recommended for calculation:
ReH ≥ 0.5 Rm.
6.4.2 Impact test shall be carried out for steel tubes with designations of 25Mn and Q345B (C, D and E) and wall thickness not less than 10 mm. Impact test is not required when the dimension of steel tube is not enough to process 10 mm×5 mm specimen. The impact absorbed energy in Table 8 is the Charpy V-notch impact absorbed energy of the normal-dimension specimen. When a small-dimension specimen is adopted for the impact test, the Charpy V-notch impact absorbed energy shall have a value of the impact absorbed energy value required for a normal-dimension specimen multiplied by the decreasing coefficient in Table 8.
Table 8 Decreasing coefficient for impact absorbed energy
Specification of specimen Dimensions of specimen (high × width) / (mm × mm) Decreasing coefficient
Standard specimen 10 × 10 1.00
Small specimen 10 × 7.5 0.75
Small specimen 10 × 5 0.50
6.5 Processing Property
6.5.1 Flattening test
As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, flattening test may be conducted for those steel tubes with wall thickness and outside diameter ratio of less than 15%, designation of 20, Q345 and 25Mn, and states of +A and +N. After the flattening test, no cracks or fissures are allowed on the specimen. The distance H of flat plates for flattening specimens shall be calculated according to FormulaEquation (1).
(1)
where,
H — the distance of flat plates, mm;
D — the nominal outer diameter of steel tubes, mm;
S — the nominal wall thickness of steel tubes, mm;
C — the deformation coefficient in unit length, 0.07 for Q345 and 25Mn steel, and 0.09 for 20 steel.
6.5.2 Flaring test
As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, for 20, Q345 and 25Mn steel tubes with an outer diameter of not greater than 150 mm and a wall thickness of not greater than 10 mm, a flaring test may be conducted. Taper of flared top core is 60°. After flaring, the flaring rate of outer diameter of the specimen shall meet the requirements specified in Table 9, and the specimen shall be free of cracks or fissures.
Table 9 The flaring rate of outer diameter of steel tube
Steel designation Flaring rate/%
Wall thickness S ≤ 4 mm Wall thickness S ≤ 4 mm
20 18 12
Q345 15 10
25Mn 13 8
6.6 Non-destructive testing
As required by the purchaser and indicated in the contract upon the agreement between the supplier and the purchaser, non-destructive testing may be conducted for steel tubes. For non-destructive testing, eddy current inspection shall be conducted according to the acceptance level B in GB/T 7735-2004, or magnetic flux leakage inspection shall be conducted according to the acceptance level F3 in GB/T 12606-2016.
6.7 Surface roughness
If the purchaser has special requirements for surface roughness, it shall be indicated in the contract. The surface roughness parameters shall be measured according to the contour arithmetic mean deviation Ra specified in GB/T 1031, and the value of surface roughness and the sampling length during measurement shall be negotiated by the supplier and the purchaser.
6.8 Surface quality
The inner and outer surfaces of steel tube shall be free from crack, wrinkle, fold, lamination and scar. These defects shall be totally removed, and the actual wall thickness at removal position shall not be less than the permissible minimum of wall thickness.
The inner and outer surfaces of steel tubes are allowed the phosphate and lubricant adhesion layers from the manufacturing process, and the inner and outer surfaces of steel tubes delivered in thermal treatment state are allowed the oxide film layers that do not affect the surface inspection.
6.9 Grain size
The actual grain size of steel tubes shall not be lower than Grade 5.
7 Test method
7.1 For the chemical composition analysis of steel tubes, samples shall be taken in accordance with GB/T 20066. For chemical composition, the spectral analysis method shall meet GB/T 4336 and GB/T 20125, the chemical analysis method shall be carried out according to GB/T 223.5, GB/T 223.12, GB/T 223.23, GB/T 223.26, GB/T 223.53, GB/T 223.59, GB/T 223.63, GB/T 223.68, GB/T 223.69 and GB/T 20123, but the arbitration analysis shouldall be carried out in accordance with the provisions of the chemical analysis method.
7.2 The dimension and shape of steel tubes shall be measured one by one with measuring instruments meeting the precision requirements.
7.3 The inner and outer surfaces of steel tubes shall be inspected visually one by one at sufficient lighting condition.
7.4 Sampling quantity and methods as well as the test methods of steel tubes for other inspection items shall be in accordance with those specified in Table 10.
Table 10 Inspection items, sampling quantity and method, and test method of steel tubes
No. Inspection item Sampling quantity Sampling method Test method
1 Chemical composition Taking one specimen from each furnace GB/T 20066 According to Article 7.1
2 Tensile test Respectively taking 1 specimen from 2 steel tubes of each batch GB/T 2975 GB/T 228.1
3 Impact test Respectively taking 3 specimen from 2 steel tubes of each batch GB/T 2975 GB/T 229
4 Flattening test Respectively taking 1 specimen from 2 steel tubes of each batch GB/T 246 GB/T 246
5 Flaring test Respectively taking 1 specimen from 2 steel tubes of each batch GB/T 242 GB/T 242
6 Eddy current testing One by one — GB/T 7735
7 Magnetic flux leakage inspection One by one — GB/T 12606
8 Surface roughness inspection Respectively taking 1 specimen from 2 steel tubes of each batch GB/T 1031 GB/T 1031
9 Grain size Respectively taking 1 specimen from 2 steel tubes of each batch GB/T 6394 GB/T 6394
8 Inspection rules
8.1 Inspection and acceptance
The inspection and acceptance of steel tubes shall be carried out by the supplier's quality and technical supervision department.
8.2 Batching rules
The inspection and acceptance of steel tubes shall be carried out by batch. Each batch shall be composed of the steel tubes with the same designation, same furnace number, same specification, same thermal treatment system (melt) or same delivery state. The maximum steel tube quantity of each batch is 200.
8.3 Sampling quantity
As for each batch of steel tubes, the sampling quantity for each inspection item shall be in accordance with those specified in Table 10.
8.4 Re-inspection and judgment rules
The re-inspection and judgment rules for steel tubes shall be in accordance with those specified in GB/T 2102.
9 Packaging, marking and quality certificate
9.1 Before leaving the factory, the inner and outer surfaces of steel tubes shall be anti-rust treated, and neutral oil shall be generally applied. Special requirements (if any) may be determined through negotiation between the supplier and the purchaser.
9.2 The packaging, marking and quality certificate of steel tubes shall be in accordance with the provisions of GB/T 2102.
