GB/T 37610-2019Corrosion-resistant alloy small diameter precision seamless tubes (English PDF)

4.1 Outer diameter and wall thickness

4.1.1 General size of alloy tubes: nominal outer diameter is 3.0mm~30mm, and nominal wall thickness is 0.3mm~3.0mm.

4.1.2 Unless otherwise specified in contract, alloy tubes are delivered according to nominal outer diameter (D) and nominal wall thickness (S). Allowable deviations of nominal outer diameter (D) and nominal wall thickness (S) shall comply with provisions on Group I in Table 1. According to purchaser's requirements and agreed by supplier and purchaser, allowable deviation of alloy tubes shall be in accordance with requirements for Group II in Table 1.

4.1.3 According to purchaser's requirements and agreed by supplier and purchaser, when alloy tubes are delivered according to minimum wall thickness Smin, allowable deviation of minimum wall thickness Smin shall comply with provisions of Table 2.

4.1.4 Agreed by supplier and purchaser, alloy tubes of other specifications outside Table 1 and Table 2 can be supplied. Allowable deviations shall be indicated in contract.

Alloy tube size Group I Group II Nominal outer diameter D Nominal wall thickness

4.2 Length

4.2.1 General length

General length of alloy tubes is 1000mm~15000mm. According to purchaser's requirements, agreed by supplier and purchaser and indicated in contract, alloy tubes of other lengths can be supplied.

4.2.2 Fixed length and multiplied length

Agreed by supplier and purchaser and indicated in contract, alloy tubes of fixed length and multiplied length can be supplied. Fixed length and multiplied length shall be within general length range. Allowable deviation of fixed length is mm. Allowable deviation of multiplied length is mm. Each multiple length shall leave a fracture allowance of 3mm~5mm.

4.3 Degree of curvature

Degree of curvature of alloy tubes shall not exceed 1.5mm/m. Degree of curvature of full length shall not exceed 0.15% of total length. For alloy tubes of which length is less than 1000mm, degree of curvature shall not exceed 1mm/m.

Requirements for other degrees of curvature shall be indicated in contract.

4.4 Un-roundness and uneven wall thickness

Un-roundness and uneven wall thickness of alloy tubes shall not exceed 80% of outer diameter tolerance and wall thickness tolerance, respectively.

4.5 End face shape

End face shapes of both ends of alloy tube shall be perpendicular to axis of alloy tube. There shall be no burrs on tube ends.

5.1 Designation and chemical composition

5.1.1 Designation and chemical composition (smelting analysis) of alloy tubes shall comply with provisions of Table 3.

5.1.2 Allowable deviation of chemical composition of finished alloy tubes shall comply with provisions of GB/T 15007.

NOTE: Compositions of P, S of some designations in the table are stricter than GB/T 15007.

5.2 Production method

5.2.1 Smelting method

Alloy shall use electric arc furnace plus outside-furnace refining plus electro-slag re-melting to smelt. It can also use other methods that be able to meet requirements of this Standard to smelt. Smelting method shall be indicated in quality certificate.

5.2.2 Tube production method

5.2.2.1 Alloy ingots for tube production shall be hot-rolled or hot-forged to round bars. On round bars, parts that are equivalent to alloy ingot head and tail shall be completely cut off.

5.2.2.2 Round bars shall use hot extrusion method to open blank. Cold-rolling of alloy tubes shall use cold-rolling (drawing) to produce.

5.3 Delivery state

5.3.1 Alloy tubes shall be delivered in state of protective atmosphere heat treatment or vacuum heat treatment. See Table 4 for recommended heat treatment system.

5.3.2 According to purchaser's requirements, alloy tubes can be delivered in cold-rolling (drawing) state.

5.4 Mechanical properties

5.4.1 Tensile at room temperature

Longitudinal tensile properties at room temperature of alloy tubes in delivery state shall comply with provisions of Table 4. Indicators of mechanical properties of alloy tubes delivered in cold-rolling (drawing) state shall be determined by supplier and purchaser via negotiation and indicated in contract.

5.4.2 Hardness

Alloy tubes used for instrumentation system shall be subject to hardness test.

Test methods and requirements shall be determined by supplier and purchaser through negotiation.

No. Unified digital code Alloy designation Recommended heat treatment system Tensile strength Rm/MPa Specified plastic extension strength Rp0.2/MPa Elongation after break A/% Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Instant cooling Annealing, 870°C~980°C, instant cooling Quench annealing, 980°C~1150°C, instant cooling Quench annealing, 940°C~1100°C, instant cooling Aging treatment, 718°C~760°C, cooling with furnace No. Unified digital code Alloy designation Recommended heat treatment system Tensile strength Rm/MPa Specified plastic extension strength Rp0.2/MPa Elongation after break A/% Annealing, 815°C~925°C, instant cooling Stress relief, 480°C~705°C, instant cooling Annealing,760°C~870°C, instant cooling Stress relief, 480°C~705°C, instant cooling Annealing,870°C~980°C, instant cooling Stress relief, 540°C~565°C, instant cooling a Steel level 1 uses annealing. Steel level 2 uses quench annealing. b If NS4301 alloy tubes are delivered in aging treatment state, mechanical properties of quench annealing state are only used as reference. c Insulation time shall not be less than 3h.

5.5 Grain size

Average grain size of NS1102, NS1104 alloy tubes shall be level 5 or more coarse. Average grain size of NS1103, NS1402, and NS3105 alloy tubes shall be level 5 and finer. Grain size of NS4301 alloy tube shall be level 3 or finer.

Agreed by supplier and purchaser and indicated in contract, requirements for other grain sizes can be specified.

5.7 Process performance

5.7.1 Flaring test

Alloy tubes shall be subject to flaring test. Top core taper of flaring test is 30° (outer diameter is not more than 10mm) or 60° (outer diameter is more than 10mm). Flaring rate of outer diameter of flared sample shall not be less than 30% of nominal outer diameter. Flared sample shall not have cracks. Alloy tubes that are delivered in cold-rolling (drawing), that are delivered in stress relief heat treatment state and aging treatment state, have no requirements for flaring test.

5.7.2 Flattening test

5.7.2.1 Alloy tubes shall be subject to flattening test. After sample is flattened, distance between two plates H is calculated according to formula (1); Where, H - Distance between two plates after being flattened, in millimeters (mm); alpha - Deformation coefficient of unit length;

S - Nominal wall thickness of alloy tube, in millimeters (mm);

D - Nominal outer diameter of alloy tube, in millimeters (mm).

5.7.2.2 When sample is flattened to distance between two plates H, there shall be no cracks on surface outside sample. Slight cracks on sample corner shall not be basis for determination. For alloy tubes that are delivered in cold-rolling (drawing) state, stress relief heat treatment state and aging treatment state, there are no requirements for flattening test.

5.8 Ultrasonic testing

5.8.1 For alloy tubes of which nominal outer diameter is not less than 6mm, it shall perform ultrasonic testing on inner and outer surfaces. Acceptance level shall comply with provisions on level L2 in GB/T 5777-2008. For alloy tubes of which nominal outer diameter is less than 6mm, it shall perform ultrasonic testing for last intermediate straight tube of 6mm or before 6mm. Acceptance level shall comply with provisions on level L2 in GB/T 5777-2008.

5.8.2 According to purchaser's requirements, agreed by supplier and purchaser and indicated in contract, ultrasonic testing can use other acceptance levels.

5.9 Eddy current testing

Alloy tubes shall be subject to eddy current testing. Acceptance level shall comply with provisions on level E1H in GB/T 7735-2016. Agreed by supplier and purchaser and indicated in contract, eddy current testing can use other acceptance levels.

5.10 Surface quality

5.10.1 There shall be no defects such as cracks, folds, rolls, separation and crusting on inner and outer surfaces of alloy tubes. These defects shall be cleared. Surface of alloy tube at clearing shall be smooth, without edges and corners. Actual wall thickness at clearing shall not be less than minimum value allowed by wall thickness.

5.10.2 Other slight surface scratches, straightening stamps, and cold rolling waves that do not exceed allowable deviation are allowed. On outer surface of alloy tube, allowable scratch depth is not greater than 3% of nominal wall thickness or 0.05mm. Take the larger of two.

5.10.3 For tubes used for instrumentation system, outer surface roughness Ra shall not exceed 0.80µm.

5.10.4 Inner and outer surfaces of alloy tubes shall be clean. There shall be no foreign matter such as oil, dust and debris. There shall be no corrosive medium such as residual acid or lye.

5.11 Special requirements

According to purchaser's requirements, agreed by supplier and purchaser and indicated in contract, it shall perform following inspections to alloy tubes:

a) high-temperature tensile test;

b) hydraulic test or underwater airtight test;

c) intergranular corrosion test;

d) other pressure test;

e) delivery in other heat treatment systems; f) others.

7.1 Inspection and acceptance

Inspection and acceptance of alloy tubes are carried out by supplier's technical quality supervision department. Purchaser has right to inspect and accept alloy tubes according to provisions of this Standard.

7.2 Batching rules

Alloy tubes are inspected and accepted in batches. Each batch shall consist of alloy tubes of same designation, same furnace number, same specification, same production method and same heat treatment system (or furnace time).

7.3 Sampling quantity and sampling site

Sampling quantity and sampling site of alloy tubes shall comply with provisions of Table 6.

7.4 Re-inspection and determination rules

Re-inspection and determination rules of alloy tubes shall comply with provisions of GB/T 2102. It is allowed to re-perform heat treatment (not exceeding twice) to alloy tubes that re-inspection result is rejected, as a new batch submitted for acceptance. Re-performance of heat treatment shall be indicated in quality certificate.