GB 5310
Seamless steel tubes and pipes for high pressure boiler
 
1 Scope
This standard specifies the classification, code, size, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certificates of seamless steel tubes for high pressure boilers.
This standard is applicable to steam boilers and pipeline seamless pipes for the manufacture of high pressure and above.
 
 
2 Normative references
 
 
3 classification, code
The seamless steel pipes of this standard are divided into two categories according to the manufacturing methods of the products. The categories and codes are as follows:
a) hot rolled steel pipe, codenamed WH;
b) Cold drawn steel pipe, codenamed WC.
 
 
4 Ordering content
Contracts or orders for ordering steel pipes in accordance with this standard shall include the following:
a) standard number;
b) product name;
c) the grade of the steel;
d) the quantity ordered (total weight or total length);
e) Dimensions (outer diameter × specified minimum wall thickness or outer diameter × average wall thickness in millimeters);
f) Special requirements.
 
 
5 size, shape and weight
5.1 Outer diameter and wall thickness
5.1.1 Unless otherwise specified in the contract, when the outer diameter (D) of the steel pipe is ≤ 127 mm, the steel pipe is delivered according to the outer diameter and the specified minimum wall thickness (Smin); when the outer diameter of the steel pipe is > 127 mm, the steel pipe is externally Delivery of diameter and nominal wall thickness (S).
 5.1.2 The outer diameter and wall thickness of steel pipes (Smin and S) shall comply with the requirements of Tables 1 and 3 of GB/T 17395. According to the requirements of the purchaser, steel pipes of different sizes as specified in Tables 1 and 3 of GB/T 17395 may be supplied through negotiation between the supplier and the buyer.
 Note: Unless otherwise stated, the wall thicknesses specified in this standard include the specified minimum wall thickness and nominal wall thickness.
 5.1.3 When the steel pipe is delivered according to the outer diameter and the specified minimum wall thickness, the allowable deviation of the outer diameter of the steel pipe shall comply with the provisions of Table 1. The allowable deviation of the wall thickness shall comply with the requirements of Table 2.
 When the steel pipe is delivered according to the outer diameter and the nominal wall thickness, the allowable deviation of the outer diameter of the steel pipe and the nominal wall thickness shall comply with the requirements of Table 1.
 
5.1.4 When the demand side does not indicate the allowable deviation level of the steel pipe in the contract, the allowable deviation of the outer diameter and wall thickness of the steel pipe shall comply with the general level.
 
According to the requirements of the purchaser, after consultation between the supplier and the buyer, and in the contract, the steel pipe with the allowable deviation of the dimensions specified in Tables 1 and 2 can be supplied.
Table 1 Allowable Tolerance of outer diameter and nominal wall thickness of steel pipe
 

Type of steel pipe	Outer diameter(mm)			Tolerance
				ordinary	advanced
Hot rolled tube	OD	≤50		±0.40	±0.30
		＞50～≤325	WT≤35	±0.75%	±0.5%
			WT＞35	±1%	±0.75%
		＞325		±1%	±0.75%
	WT	≤4.0		±0.4	±0.3
		＞4.0～≤20		±10%	±7.5%
		＞20	OD＜219	±10%	±7.5%
			OD≥219	+12.5%  -10%	±10%

Cold drawn tube	OD	≤25.4	±0.15	—
		＞25.4～≤40	±0.20	—
		＞40～≤50	±0.25	—
		＞50～≤60	±0.30	—
		＞60	±0.5%	—
	WT	≤2.8	±0.2	—
		＞2.8	±7.5%	—

Table 2 Allowable Tolerance of the minimum wall thickness specified in the steel pipe
 

Type of steel pipe	Wall thickness range	Tolerance
		ordinary	advanced
Hot rolled tube	WTmin≤4.0	+0.8 O	+0.6 O
	WTmin＞4.0	+20%S 0	+15%S 0
Cold drawn tube	WWTmin≤2.8	+0.4 O	—
	WTmin＞2.8	+15%S 0	—

 
5.2 length
5.2.1 Normal length
Steel pipes usually have a length of 4 000 mm to 12 000 mm.
Short-term steel pipes of not less than 3 000 mm in length may be delivered through negotiation between the supplier and the purchaser, but the quantity shall not exceed 5% of the total delivered quantity of the batch of steel pipes.
 
5.2.2 Length and length of the ruler
According to the requirements of the purchaser and stated in the contract, the steel pipe can be delivered according to the length of the fixed length or the length of the double. The length of the steel pipe or the total length of the double-length pipe shall be within the normal length. The full-length allowable deviation shall comply with the following requirements:
a) length ≤ 6 000 mm, 0 to 10 mm;
b) Length > 6 000 mm, 0 to 15 mm.
The length of each double ruler should be set as follows:
a) OD ≤ 159 mm, 5 mm to 10 mm;
b) Outside diameter > 159 mm, 10 mm to 15 mm.
 
5.3 Curvature
The bending per meter of steel pipe should meet the following requirements:
a) ≤1.5 mm/m when the wall thickness is ≤15 mm;
b) when the wall thickness is >15 mm to 30 mm, ≤2.0 mm/m;
c) ≤ 3.0 mm/m when wall thickness > 30 mm.
The full-length bending of the header tube should be no more than 12 mm.
 
5.4 Unroundness and uneven wall thickness
According to the requirements of the purchaser, the supplier and the buyer shall negotiate and indicate in the contract that the non-roundness and wall thickness of the steel pipe shall not exceed 80% of the outer diameter and wall thickness tolerance respectively.

5.5 Tip shape
The end faces of the steel pipe should be perpendicular to the axis of the steel pipe, and the incision burrs should be removed.
 
5.6 weight
5.6.1 Delivery weight
When the steel pipe is delivered according to the outer diameter and the specified minimum wall thickness, the steel pipe is delivered according to the actual weight; the supply and demand sides negotiate, and the contract states that the steel pipe can also be delivered according to the theoretical weight.
 When the steel pipe is delivered according to the outer diameter and the nominal wall thickness, the steel pipe is delivered according to the actual weight and can also be delivered according to the theoretical weight.
5.6.2 Calculation of theoretical weight
The theoretical weight of high-quality carbon structural steel and alloy structural steel pipe is calculated according to GB/T 17395 (the density of steel is 7.85 kg/dm3), and the theoretical weight of stainless steel (heat-resistant) steel pipe is according to GB/T 17395. Calculate 1.015 times the theoretical weight.
When calculating the theoretical weight of the steel pipe delivered according to the outer diameter and the specified minimum wall thickness, the supply and demand sides may determine the corresponding wall thickness correction coefficient according to the allowable deviation of the specified minimum wall thickness.
5.6.3 Weight tolerance
According to the requirements of the purchaser, the supplier and the buyer shall negotiate and indicate in the contract that the deviation between the theoretical weight of the delivered steel pipe and the actual weight shall comply with the following provisions:
a) single steel pipe: ±10%;
b) Steel pipes with a minimum of 10 t per batch: ± 7.5%.


6. Technical requirements
6.1 Steel grades and chemical composition
6.1.1 The grade and chemical composition (melting composition) of steel shall comply with the requirements of Table 3.
 
Table 3 Steel grades and chemical composition

Steel Pipe

Chemical Composition(%)

C

Si

Mn

Cr

Mo

V

Ti

B

Ni

Altot

Cu

Nb

N

W

P

S

Max

20G

0.17～0.23

0.17～0.37

0.35～0.65

≤0.25

≤0.15

≤0.08

—

—

≤0.25

≤0.015

≤0.20

—

—

—

0.025

0.020

20MnG

0.17～0.23

0.17～0.37

0.70～1.00

≤0.25

≤0.15

≤0.08

—

—

≤0.25

—

≤0.20

—

—

—

0.025

0.020

25MnG

0.22～0.29

0.17～0.37

0.70～1.00

≤0.25

≤0.15

≤0.08

—

—

≤0.25

—

≤0.20

—

—

—

0.025

0.020

15MoG

0.12～0.20

0.17～0.37

0.40～0.80

≤0.30

0.25～0.35

—

—

—

≤0.30

—

≤0.20

—

—

—

0.025

0.020

20MoG

0.15～0.25

0.17～0.37

0.40～0.80

≤0.30

0.44～0.65

—

—

—

≤0.30

—

≤0.20

—

—

0.025

0.020

12CrMoG

0.08～0.15

0.17～0.37

0.40～0.70

0.40～0.70

0.40～0.55

—

—

—

≤0.30

—

≤0.20

—

—

—

0.025

0.020

15CrMoG

0.12～0.18

0.17～0.37

0.40～0.70

0.80～1.10

0.40～0.55

—

—

—

≤0.30

—

≤0.20

—

—

—

0.025

0.020

12Cr2MoG

0.08～0.15

≤0.50

0.40～0.70

2.00～2.50

0.90～1.20

—

—

—

≤0.30

—

≤0.20

—

—

—

0.025

0.020

12Cr1MoVG

0.08～0.15

0.17～0.37

0.40～0.70

0.90～1.20

0.25～0.35

0.15～0.30

—

—

≤0.30

—

≤0.20

—

—

—

0.025

0.020

12Cr2MoWVTiB

0.08～0.15

0.45～0.75

0.45～0.65

1.60～2.10

0.50～0.65

0.28～0.42

0.08～0.18

0.0020～0.0080

≤0.30

—

≤0.20

—

—

0.30～0.55

0.025

0.020

07Cr2MoW2VNbB

0.04～0.10

≤0.50

0.10～0.60

1.90～2.60

0.05～0.30

0.20～0.30

—

0.0005～0.0060

≤0.30

—

≤0.20

0.02～0.08

≤0.030

1.45～1.75

0.025

0.010

08Cr2Mo1W2VTiB

0.05～0.10

0.15～0.45

0.30～0.70

2.20～2.60

0.90～1.10

0.20～0.30

0.06～0.10

0.0015～0.0070

≤0.30

≤0.02O

≤0.20

—

≤0.012

1.45～1.75

0.020

0.010

12Cr3MoVSiTiB

0.09～0.15

0.60～0.90

0.50～0.80

2.50～3.00

1.00～1.20

0.25～0.35

0.22～0.38

0.0050～0.0110

≤0.30

—

≤0.20

—

—

—

0.025

0.020

Steel Pipe

Chemical Composition(%)

C

Si

Mn

Cr

Mo

V

Ti

B

Ni

Altot

Cu

Nb

N

W

P

S

不大于

09Ni1MnMoNbCu

≤0.17

0.25～0.50

0.80～1.20

≤0.30

0.25～0.50

—

—

—

1.00～1.30

≤0.050

0.50～0.80

0.015～0.045

≤0.020

—

0.025

0.020

10Cr9Mo1VNbN

0.07～0.14

0.20～0.50

0.30～0.60

8.O0～9.50

0.85～1.05

0.18～0.25

—

—

≤0.40

≤0.04O

≤0.20

0.06～0.10

0.030～0.070

—

0.020

0.010

10Cr9MoW2VNbBN

0.07～0.13

≤0.50

0.30～0.60

8.50～9.50

0.30～0.60

0.15～0.25

—

0.0010～0.0060

≤0.40

≤0.04O

≤0.20

0.04～0.09

0.030～0.070

1.50～2.00

0.020

0.010

10Cr11MoW2VNbCu1BN

0.07～0.14

≤0.50

≤0.70

10.00～12.50

0.25～0.60

0.15～0.30

—

0.0005～0.0050

≤0.50

≤0.04O

0.30～1.70

0.04～0.10

0.040～0.100

1.50～2.50

0.020

0.010

11Cr9Mo1W1VNbBN

0.09～0.13

0.10～0.50

0.30～0.60

8.50～9.50

0.90～1.10

0.18～0.25

—

0.0003～0.0060

≤0.40

≤0.04O

≤0.20

0.06～0.10

0.040～0.090

0.90～1.10

0.020

0.010

15Cr18Ni9

≤0.15

≤1.00

≤2.00

17.00～19.00

—

—

—

8.00～10.00

—

—

—

≤0.01

—

0.030

0.015

10Cr18Ni9NbCu3BN

0.07～0.13

≤0.30

≤0.50

17.00～19.00

—

—

—

0.0010～0.0100

7.50～10.50

0.003～0.030

2.50～3.50

0.20～0.60

0.050～0.120

—

0.030

0.015

07Cr25Ni21NbN

0.04～0.10

≤1.00

≤2.00

24.00～26.00

—

—

—

19.00～22.00

—

—

0.20～0.60

0.15～0.35

—

0.030

0.015

08Cr18Ni11Nb

≤0.08

≤1.00

≤2.00

17.00～19.00

—

—

—

—

9.00～12.00

—

—

10C～1.10

—

—

0.030

0.015

07Cr18Ni11Nb

0.04～0.10

≤1.00

≤2.00

17.00～19.00

—

—

—

—

9.00～12.00

—

—

8C～1.10

—

—

0.030

0.015

08Cr18Ni11NbFG

0.06～0.10

≤1.00

≤2.00

17.00～19.00

—

—

—

—

9.00～12.00

—

—

8C～1.10

—

—

0.030

0.015

6.1.2 Steel pipes should be analyzed for chemical composition of finished products. The chemical composition allowable deviation of the finished steel pipe shall comply with the provisions of GB/T 222.
 
6.2 Manufacturing methods
6.2.1 Steel smelting method
High-quality carbon structural steel and alloy structural steel shall be smelted by electric furnace plus furnace refining, oxygen converter plus furnace refining or electroslag remelting method, and steel refined outside the furnace shall be subjected to vacuum degassing treatment.
 
10Cr9Mo1VNbN, 10Cr9MoW2VNbBN, 10Cr11MoW2VNbCu1BN, 11Cr9Mo1W1VNbBN and stainless (heat-resistant) steel should be smelted by electric furnace plus furnace refining or electroslag remelting. The steel refined outside the furnace should be vacuum degassed.
 
After consultation between the supplier and the buyer, and indicating in the contract, other higher-required smelting methods may be adopted. When the purchaser specifies a certain smelting method, it should be indicated in the contract.
 
6.2.2 Manufacturing methods and requirements for tube blanks
The tube blank can be produced by continuous casting, die casting or hot rolling (forging).
Continuous casting tube blanks shall comply with the provisions of YB/T 4149, in which the level of low-fold structural defects shall not exceed 1; the hot-rolled (forged) tube blanks shall comply with the provisions of YB/T ××××; It is carried out in accordance with the regulations for hot-rolled (forged) tube blanks.
 
6.2.3 Manufacturing method of steel pipe
Steel pipes shall be manufactured by hot rolling (extrusion, expansion) or cold drawing (rolling). Steel pipes of grade 08Cr18Ni11NbFG shall be manufactured by cold drawing (rolling) seamless method.
 
6.3 Delivery status
The steel pipe shall be delivered in a heat treated condition. The heat treatment system for steel pipes shall comply with the requirements of Table 4. The heat treatment system for steel pipes should be filled in the quality certificate.
 
Table 4 Heat treatment system for steel pipes

	Steel Pipe	Heat treatment
1	12Ga、20Ga	880 ℃～940 ℃,Normalizing
2	20MnGa、25MnGa	880 ℃～940 ℃,Normalizing
3	15MoGa、20MoGa	890 ℃～950 ℃,Normalizing
4	12CrMoGa	900 ℃～960 ℃,Normalizing；650 ℃～730 ℃,Tempering
5	15CrMoGa	900 ℃～960 ℃,Normalizing；660 ℃～730 ℃,Tempering
6	12Cr2MoGa	900 ℃～960 ℃,Normalizing；700 ℃～750 ℃,Tempering It can also be heated to 900 °C ~ 960 °C, and the furnace is cooled to 700 °C for more than 1 h, and air-cooled.
7	12Cr1MoVGa	980 ℃～1 020 ℃,Normalizing，980 °C ~ 1 020 °C normalizing, when the wall thickness is greater than 30 mm, forced cooling; 720 °C ~ 760 °C tempering.
8	12Cr2MoWVTiB	1 000 ℃～1 035 ℃,Normalizing；760 ℃～790 ℃,Tempering
9	07Cr2MoW2VNbB	≥1 040 ℃,Normalizing，≥730 ℃,Tempering
10	08Cr2Mo1W2VTiB	≥980 ℃,Normalizing，≥730 ℃,Tempering
11	12Cr3MoVSiTiB	1 040 ℃～1 060 ℃,Normalizing；720 ℃～770 ℃,Tempering
12	09Ni1MnMoNbCu	880 ℃～980 ℃,Normalizing，580 ℃～680 ℃,Tempering
13	10Cr9Mo1VNbN	≥1 040 ℃,Normalizing，≥730 ℃,Tempering
14	10Cr9MoW2VNbBN	≥1 040 ℃,Normalizing，≥730 ℃,Tempering
15	10Cr11MoW2VNbCu1BN	≥1 040 ℃,Normalizing，≥730 ℃,Tempering
16	11Cr9Mo1W1VNbBN	1 040 ℃～1 080 ℃,Normalizing，740 ℃～780 ℃,Tempering
17	15Cr18Ni9b	Solution treatment: solution temperature ≥1 040 °C.
18	10Cr18Ni9NbCu3BNb	Solution treatment: solution temperature ≥ 1 100 °C.
19	07Cr25Ni21NbNcd	Separate solution treatment: solution temperature ≥ 1 100 °C.
20	08Cr18Ni11Nbbd	Solution treatment: solution temperature ≥1 040 °C.
21	07Cr18Ni11Nbcd	Separate solution treatment: hot rolling (extrusion, expansion) steel tube solid solution temperature ≥ 1 050 °C, cold drawn (rolled) steel tube solid solution temperature ≥ 1100 °C.
22	08Cr18Ni10NbFG	Softening heat treatment before cold working: softening heat treatment temperature should be at least 50 °C higher than solution heat treatment temperature; solution treatment after final cold working: solution temperature ≥1 180 °C
a. The finishing temperature of the hot-rolled steel pipe is at the critical temperature of the phase transition Ar3 to the upper limit of the temperature specified in the table, and when the steel pipe is air-cooled, the steel pipe is considered to be normalized.   b. The finishing temperature of the hot-rolled steel pipe meets the solid solution temperature specified in the table. As an alternative to the solid solution treatment method, the steel pipe can be separately quenched by water or cooled by other fast enough methods.   c, the solution treatment should be a separate heat treatment, and the heat treatment in the process is not allowed to replace the separate solution treatment.   d. According to the requirements of the purchaser, the steel pipes of the grades 07Cr25Ni21NbN, 08Cr19Ni10Nb and 07Cr18Ni11Nb may be subjected to a stabilization heat treatment lower than the initial solution treatment temperature after the solution treatment, and the temperature of the stabilization heat treatment is negotiated between the supplier and the purchaser.

 
 
6.4 Mechanical properties
6.4.1 Delivery conditions The room temperature mechanical properties of steel pipes are to comply with the requirements of Table 5.
Table 5 Mechanical properties of steel pipes
 

	Steel Pipe	Tensile properties				Impact energy(Akv)，J		Hardness
		Tensile strength (MPa)	Yield Strength (MPa)	Elongation %		Portrait	Landscape	A	B	C
								HBW	HV	HRC
				Portrait	Landscape
			Max					Min
1	12G	≥325	180	35	33	40	27	137	—	77HRB
2	20Ga	410～550	245	24	22	40	27	—	—	—
3	20MnGa	≥415	240	22	20	40	27	—	—	—
4	25MnGa	≥485	275	20	18	40	27	—	—	—
5	15MoGa	450～600	270	22	20	40	27	—	—	—
6	20MoGa	≥415	220	22	20	40	27	—	—	—
7	12CrMoG	410～560	205	21	19	40	27	156	165	83HRB
8	15CrMoG	440～640	235	21	19	40	27	170	180	88HRB
9	12Cr2MoG	450～600	280	20	18	40	27	163	170	85HRB
10	12Cr1MoVGa	470～640	255	21	19	40	27	—	—	—
11	12Cr2MoWVTiBa	540～735	345	18	16	40	27	—	—	—
12	07Cr2MoW2VNbB	≥510	400	20	18	40	27	220	230	97HRB
13	08Cr2Mo1W2VTiB	≥585	415	20	18	40	27	250	265	25
14	12Cr3MoVSiTiBa	610～805	440	16	14	40	27	—	—	—
15	09Ni1MnMoNbCu	610～780	440	19	17	40	27	252	270	25
16	10Cr9Mo1VNbN	≥585	415	20	18	40	27	250	265	25
17	10Cr9MoW2VNbBN	≥620	440	20	18	40	27	250	265	25
18	10Cr11MoW2VNbCu1BN	≥620	400	20	18	40	27	250	265	25
19	11Cr9Mo1W1VNbBN	≥620	440	20	18	40	27	250	265	25
20	15Cr18Ni9	≥520	205	35	—	—	—	192	200	90HRB
21	10Cr18Ni9NbCu3BN	≥550	205	35	—	—	—	192	200	90HRB
22	07Cr25Ni21NbN	≥655	295	30	—	—	—	256	—	100HRB
23	08Cr18Ni11Nb	≥520	205	35	—	—	—	192	200	90HRB
24	07Cr18Ni11Nb	≥520	205	35	—	—	—	192	200	90HRB
25	08Cr18Ni10NbFG	≥550	205	35	—	—	—	192	200	90HRB

 
 
6.4.2 The impact energy in Table 5 is the impact energy of a full-size standard sample. The impact energy (Akv.p) measured by the small-sized sample is converted into the impact energy (Akv. C) of the standard sample according to the formula (1).
 
Akv.C=10Akv.p/W....................................(1)
 
In the formula:
Akv.C - Calculate the impact energy of standard specimens in joules (J);
Akv.p - impact energy measured in small size specimens, in joules (J);
W——The width of the sample in millimeters (mm).
The calculation of the standard sample impact energy (Akv.C) should be in accordance with Akv in Table 5.

6.4.3 The hardness of steel pipes should meet the following requirements:
a) Alloy structural steel pipe and stainless steel (heat-resistant) steel pipe with outer diameter ≤ 127 mm shall be tested for hardness, and the hardness value shall comply with the provisions of Table 5;
 
b) According to the requirements of the purchaser, the high-quality carbon structural steel pipe and the alloy structural steel pipe with the outer diameter >127 mm can be used for hardness requirements. The hardness value can be as specified in Table 5.
 
6.4.3 The hardness test of steel pipes shall meet the following requirements:
a) Steel pipes with wall thickness ≥ 5.0 mm shall be subjected to Brinell hardness test or Rockwell hardness test;
b) Steel pipes with wall thickness <5.0 mm but ≥1.7 mm shall be tested for Rockwell hardness;
c) Steel pipes with a wall thickness <1.7 mm shall not be subjected to a hardness test;
d) When the purchaser stipulates in the contract that the steel pipe is subjected to the Vickers hardness test, the Vickers hardness test shall be performed.
 
6.4.4 According to the requirements of the purchaser, the supplier and the buyer shall negotiate and indicate the test temperature in the contract, and the supplier shall be able to do the high temperature regulation non-proportional extension strength (Rp0.2) test of the steel pipe.

6.5 Process performance
6.5.1 Hydraulic test
The steel pipe shall be hydraulically tested one by one, and the supplier may use eddy current testing instead of the hydraulic test.
 
6.5.2 Flattening test
6.5.2.1 Steel pipes with an outer diameter greater than 22 mm to 400 mm and a wall thickness not greater than 40 mm shall be subjected to a flattening test.
6.5.3 Bending test
Steel pipes with an outer diameter greater than 400 mm or a wall thickness greater than 40 mm shall be subjected to a bending test. The bending test is a forward bending of the outer surface of the steel tube under tensile deformation.
 
The bending core diameter of the bending test shall be 3 times of the thickness of the specimen, and the bending specimen shall be bent to 180 ° at room temperature (when the axial center of the bending core is lower than the axial center of the two rollers during the test, the test may be considered The bending angle is up to 180°).
After the bending test, cracks or cracks visible to the naked eye are not allowed on the curved outer surface and side of the specimen
 
6.5.4 Flaring test
According to the requirements of the purchaser, and in the contract, the steel pipe with an outer diameter of not more than 76 mm and a wall thickness of not more than 8 mm can be used for the flare test.
The flaring test was carried out at room temperature with a top core taper of 60°. The flaring ratio of the outer diameter of the sample after flaring shall comply with the provisions of Table 6. After the flaring, the sample shall not allow cracks or cracks.
 
Table 6 Steel pipe outer diameter expansion rate

Type of steel pipe	Steel pipe outer diameter expansion rate, %
	Inside diameter / Outer diameter
	≤0.6	＞0.6～0.8	＞0.8
High quality carbon structural steel pipe	10	12	17
Alloy structural steel pipe	8	10	15
Stainless (heat resistant) steel pipe	12	15	20

6.6 Low-power test
Steel pipes should be tested at low magnification. Visually visible white spots, inclusions, subcutaneous bubbles, tumbling and delamination are not allowed on the cross-section acid immersion test piece.

6.7 Non-metallic inclusions
Steel pipes shall be tested for non-metallic inclusions. The non-metallic inclusions of steel pipes are rated according to the A method of GB/T 10561, and the fine and coarse grades of various inclusions of A, B, C, D and DS should be no more than 2.5, and all kinds of inclusions. The total number of fine-level levels and the total number of coarse-level levels should each be no more than 6.5.
 
According to the requirements of the purchaser, the supplier and the buyer shall negotiate and indicate in the contract that the non-metallic inclusion inspection of the finished steel pipe may require a stricter level.
 
6.8 grain size
The finished steel pipe should be tested for grain size.
 
6.9 Microstructure
The microstructure of the finished steel pipe shall comply with the following regulations:
a) The finished steel pipe of high-quality carbon structural steel shall be ferrite plus pearlite, and no superheated structure shall be allowed;
b) The finished steel pipe with the grades 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12Cr1MoVG, 15NiMnMoCuNb shall be ferrite plus pearlite, allowing the presence of granular bainite, and no phase change critical temperature between AC1 and AC3 is allowed. Complete phase change product (such as yellow bar martensite); the finished steel pipe of grade 12Cr1MoVG allows the presence of sorbite;
c) The finished steel pipe with the grades 12Cr2MoWVTiB, 12Cr3MoVSiTiB, 07Cr2MoW2VNbB and 08Cr2Mo1W2VTiB shall be tempered bainite, allowing the presence of sorbite or tempered martensite, and free ferrite is not allowed;
d) The finished steel pipes of the grades 10Cr9Mo1VNbN, 10Cr9MoW2VNbBN, 10Cr11MoW2VNbCu1N and 11Cr9Mo1W1VNbBN shall be tempered martensite;
e) Stainless steel (heat resistant) steel finished steel pipe should be austenite.
 
6.10 Decarburization layer
Cold drawn (rolled) finished steel pipes with an outer diameter of not more than 76 mm shall be inspected for the total decarburization layer. The depth of the outer surface of the total decarburization layer shall not exceed 0.3 mm, and the depth of the inner surface shall be no more than 0.4 mm, and the sum of the two shall not exceed 0.6 mm.
 
6.11 Intergranular corrosion test
According to the requirements of the purchaser, the supply and demand sides negotiate and indicate in the contract that the stainless steel pipe can be used for intergranular corrosion test. The intergranular corrosion test method is carried out according to GB/T 4334.5, and the other party may specify other corrosion test methods.
 
6.12 Surface quality
6.12.1 The inner and outer surfaces of steel pipes are not allowed to have cracks, folds, crusting, rolling and separation. These defects shall be completely removed and the depth of defect removal shall not exceed 10% of the wall thickness. The actual outer diameter and wall thickness of the defect removal shall not be less than the minimum allowable for the outer diameter and wall thickness.
 
The allowable depth or height of the straight road on the inner and outer surfaces of the steel pipe shall comply with the following requirements:
a) cold drawn (rolled) steel pipe: not more than 4% of the nominal wall thickness, and the maximum is 0.2 mm;
b) Hot-rolled (extruded, expanded) and forged steel pipes: not more than 5% of the nominal wall thickness and a maximum of 0.4 mm.
Other local defects that do not exceed the wall thickness allowing a negative deviation are allowed to exist.
 
6.12.2 The scale of the inner and outer surfaces of the steel pipe shall be removed, but the oxidized thin layer which does not hinder the inspection shall be allowed to exist.
 
6.13 Non-destructive testing
The steel pipe shall be ultrasonically inspected and tested in accordance with the provisions of GB/T 5777. The ultrasonic flaw detection test sample tube longitudinal groove depth grade is C5.
According to the requirements of the purchaser, after the supply and demand sides negotiate and indicate in the contract, other non-destructive tests can be added.
 
 
7 sample
7.1 Tensile test specimen
For steel pipes with an outer diameter of less than 219 mm, the tensile test shall be taken along the longitudinal direction of the steel pipe.
For steel pipes with an outer diameter of not less than 219 mm, when the steel pipe size permits, the tensile test shall take a circular cross-section sample along the transverse direction of the steel pipe; when the steel pipe is not large enough to intercept the circular cross-section specimen, the tensile test shall be along the steel pipe. Longitudinal sampling.

7.2 Impact test specimen
For steel pipes with an outer diameter of less than 219 mm, the impact test may be sampled by the manufacturer along the longitudinal or transverse direction of the steel pipe. If there is no special provision in the contract, the arbitration specimen shall be taken along the longitudinal direction of the steel pipe.
 
For steel pipes with an outer diameter of not less than 219 mm, the impact test shall be taken along the transverse direction of the steel pipe.
Whether taken along the longitudinal direction of the steel tube or transversely along the steel tube, the impact specimen should be a larger size specimen of full size, 3/4 size, 1/2 size or 1/4 size. When the steel pipe is not large enough to intercept a 1/4-size impact specimen, the steel pipe is not subjected to an impact test.
 
7.3 bending test specimen
7.3.1 Sample shape
The specimen of the bending test was an arc-shaped specimen taken along the transverse direction of the steel pipe.
 
7.3.2 Sample size
The width (b) of the specimen shall be twice the wall thickness of the steel pipe, but shall not be greater than 40 mm.
 
The thickness of the sample (a) shall be the wall thickness. When the wall thickness of the steel pipe is greater than 20 mm, one of the specimens can be thinned from the inner surface of the pipe wall to 20 mm, and the other sample can be thinned from the outer surface of the pipe wall to 20 mm.
 
7.3.3 Sample preparation
The preparation of the sample shall comply with the provisions of GB/T 232. The specimen may be machined into a shiny surface by bending and deforming the surface, but as close as possible to the original rolled surface (the outer surface of the steel tube). The specimen is bent and the deformed surface is not allowed to have obvious scratches and other defects.
 
 
8 Inspection and test methods
8.1 The size and shape of the steel pipe shall be measured one by one using gauges that meet the accuracy requirements.
8.2 The inner and outer surfaces of steel pipes shall be inspected visually by themselves under adequate lighting conditions.
 
 
9 Inspection rules
9.1 Inspection and acceptance
The inspection and acceptance of steel pipes shall be carried out by the supplier's quality and technical supervision department.
 
9.2 Batch rule
Steel pipes are inspected and accepted in batches. Each batch shall consist of steel pipes of the same grade, the same furnace (tank) number, the same specification and the same heat treatment system (heating). The number of pipes per batch shall not exceed the following:
a) outer diameter ≤ 76 mm, and wall thickness ≤ 3 mm: 400;
b) outer diameter > 351 mm: 50;
c) Other sizes: 200 pieces.
 
9.3 Number of samples
The sampling quantity of each batch of steel pipe inspection shall comply with the provisions of Table 8.
 
9.4 Re-inspection and decision rules
The re-inspection and determination rules of steel pipes shall comply with the provisions of GB/T 2102.
 
 
10 Packaging, sign and quality certificate
The packaging, marking and quality certificate of steel pipes shall comply with the provisions of GB/T 2102.