GB/T 38526-2020 Titanium Tubes for Aerospace Propulsion System China National Standard

Scope

This standard specifies the technical requirements, test methods, inspection rules, and markings, packaging, transportation, storage, quality certificate, and order (or contract) content for titanium tubing used in aerospace propulsion systems. This standard applies to titanium tubing (hereinafter referred to as tubing) produced by cold rolling (cold drawing).

Normative References

The following documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including all amendments) applies.

• GB/T 228.1-2010 Metal Materials – Tensile Testing – Part 1: Method of Test at Room Temperature
• GB/T 241 Metal Tubes – Hydraulic Test Method
• GB/T 242 Metal Tubes – Flare Test Method
• GB/T 244 Metal Tubes – Bend Test Method
• GB/T 246 Metal Materials – Tube Testing Methods
• GB/T 3620.1 Titanium and Titanium Alloy Grades and Chemical Composition
• GB/T 3620.2 Permissible Variations in Chemical Composition for Titanium and Titanium Alloy Processed Products
• GB/T 4698 (All Parts) Methods for Chemical Analysis of Sponge Titanium and Titanium Alloys
• GB/T 8180 Packaging, Marking, Transportation, and Storage of Titanium and Titanium Alloy Processed Products
• GB/T 12969.1 Ultrasonic Inspection Methods for Titanium and Titanium Alloy Tubes
• GB/T 12969.2 Eddy Current Inspection Methods for Titanium and Titanium Alloy Tubes
• GB/T 23603 Methods for Detecting Surface Contaminant Layers on Titanium and Titanium Alloys

Technical Requirements

3.1 Materials 3.1.1 The ingots used for producing the tubing shall be remelted at least twice. The first remelting may be done using a vacuum arc remelting furnace or a cold hearth furnace, and subsequent remelting shall use a vacuum arc remelting furnace, with no elements added during the final remelting. 3.1.2 Non-consumable electrodes such as tungsten electrodes should not be used for welding in vacuum arc remelting.

3.2 Grade, Condition, and Specification The grade, condition, and specification of the tubing shall conform to the requirements specified in Table 1.

Table 1: Grade, Condition, and Specification

Grade	Condition	Outer Diameter (mm)	Wall Thickness (mm)
TA1	Annealed (M)	6	○ (0.8)
		8	○ (1.0)
		10	○ (1.0)
		12	○ (1.0)
		14	○ (1.5)
		16	○ (1.5)

Note: “○” indicates that the wall thickness can be produced according to this standard, and “-” indicates that the wall thickness of the product needs to be determined through consultation. All units are in millimeters.

3.3 Chemical Composition 3.3.1 The chemical composition of the tubing shall conform to the provisions of GB/T 3620.1. 3.3.2 When the purchaser samples the tubing for chemical composition retesting, allowable deviations in composition shall comply with the provisions of GB/T 3620.2.

3.4 Dimensions and Permissible Deviations 3.4.1 Permissible deviations in outer diameter and wall thickness of the tubing shall comply with the provisions specified in Table 2.

Table 2: Outer Diameter and Wall Thickness Allowable Deviations

Outer Diameter	Wall Thickness	Allowable Deviation
A	0.8	+0.060, -0.050
6	0.8, 1.0	±0.080, -0.050
8	0.8	±0.080
10	1.0	±0.080
12	1.0	+0.100
14	1.0	±0.100
16	1.0, 1.5	±0.100, -0.050

Note: All units are in millimeters.

3.3 Chemical Composition 3.3.1 The chemical composition of the tubing shall conform to the provisions of GB/T 3620.1. 3.3.2 When the purchaser samples the tubing for chemical composition retesting, allowable deviations in composition shall comply with the provisions of GB/T 3620.2.

3.4 Dimensions and Permissible Deviations 3.4.1 Permissible deviations in outer diameter and wall thickness of the tubing shall comply with the provisions specified in Table 2.

3.4.2 The out-of-roundness of the tubing shall not exceed the permissible positive deviation of the outer diameter.

3.4.3 The indefinite length of the tubing is 1000mm to 3200mm. The fixed length or multiple lengths of the tubing shall fall within this indefinite length range. The allowable deviation for fixed length is 0mm to 10mm. The multiple lengths shall also take into account the amount of cut-off, with each cut-off amounting to 5mm.

3.4.4 The ends of the material shall be cut flat, and the slope of the cut shall not exceed 2mm.

3.4.5 The tubing’s curvature shall not exceed 3mm per meter.

3.5 Mechanical Properties
The room temperature tensile performance of the tubing shall conform to the provisions specified in Table 3.

Table 3: Room Temperature Tensile Properties

Grade	Condition	Tensile Strength (MPa)	Elongation (%)
TA1	M	345-500	>23

Note: All units are in megapascals (MPa) for tensile strength and percentage (%) for elongation.

3.6 Process Performance

3.6.1 Flaring Test
Tubing with an outer diameter not less than 6mm shall undergo a flaring test. The taper of the flare core shall be 74°. The outer diameter of the specimen after flaring shall not be less than 1.3 times the nominal outer diameter of the tubing, and there shall be no cracks at the flare location.

3.6.2 Flattening Test
The tubing shall undergo a flattening test. When flattened to the specified distance, the tubing surface shall not exhibit cracks, fissures, fractures, stretch marks, open die marks, or polished marks. The plate spacing should be calculated according to formula (1):

H=0.07×nominal wall thickness×nominal outer diameter

Here:

• HHH represents the plate spacing in millimeters (mm).
• The constant 0.070.070.07 is used in the calculation.
• “Nominal wall thickness” refers to the specified wall thickness of the tubing in millimeters (mm).
• “Nominal outer diameter” refers to the specified outer diameter of the tubing in millimeters (mm).

3.6.3 Bend Test

The tubing shall undergo a bend test. The bending radius shall be four times the nominal outer diameter of the tubing. After bending 90 degrees, there shall be no cracks at the bent section.

3.6.4 Hydraulic Test

The tubing shall undergo a hydraulic test. The tubing shall be subjected to the test pressure specified in Table 4 for a holding time of 5 seconds. After the test, the tubing shall not exhibit distortion or leakage.

Table 4: Hydraulic Test Pressure (MPa)

3.7 Surface Contamination

The tubing shall be free from any oxide-rich layers, such as alpha layers or other surface contaminants.

3.8 Non-Destructive Testing

3.8.1 Ultrasonic Testing

Tubing with an outer diameter of not less than 6mm shall undergo ultrasonic testing. The artificial U-shaped standard defect in the tubing serves as a longitudinal groove on both the inner and outer surfaces for comparison with reference samples, with dimensions as specified in Table 5.

Table 5: U-shaped Standard Defect Dimensions

Outer Diameter	U-shaped Standard Defect Dimensions
6-8	Depth: 10% of Nominal Wall Thickness
	Length: 3-5 mm
	Width: <0.3 mm
>8-16	Depth: 10% of Nominal Wall Thickness
	Length: 5-10 mm
	Width: <0.5 mm

Note: All units are in millimeters (mm).

3.8.2 Eddy Current Testing

The tubing shall undergo eddy current testing. For tubing with an outer diameter not exceeding 8mm, artificial standard hole diameters should not exceed 0.3mm. For tubing with an outer diameter greater than 8mm, artificial standard hole diameters should not exceed 0.6mm.

3.9 Surface Quality

3.9.1 The inner and outer surfaces of the tubing shall be pickled surfaces.

3.9.2 The inner surface roughness (Ra) of the tubing shall not exceed 3.2μm, and the outer surface roughness (Ra) shall not exceed 1.6μm.

3.9.3 The inner and outer surfaces of the tubing shall be clean and free from oil stains, oxidation, or other foreign substances.

3.9.4 The inner and outer surfaces of the tubing shall be free from visually detectable defects such as cracks, folds, peeling, or pinholes.

3.9.5 Local defects on the tubing surface are permissible to be removed, and after removal, the tubing wall thickness shall not exceed its allowable deviation.

3.9.6 Local scratches, pits, protrusions, and straightening marks on the tubing surface are permissible within half of the allowable wall thickness deviation.

Test Methods

4.1 Chemical composition shall be tested according to GB/T 4698.

4.2 Dimensional measurements and allowable deviations shall be inspected using gauges with appropriate accuracy.

4.3 Room temperature tensile performance shall be tested according to GB/T 228.1-2010, with S7 specimen as per 4.3.

4.4 Flaring test shall be conducted according to GB/T 242.

4.5 Flattening test shall be conducted according to GB/T 246.

4.6 Bend test shall be conducted according to GB/T 244.

4.7 Hydraulic test shall be conducted according to GB/T 241.

4.8 Surface contamination shall be inspected according to GB/T 23603, under a microscope with 100x magnification.

4.9 Ultrasonic testing shall be conducted according to GB/T 12969.1.

4.10 Eddy current testing shall be conducted according to GB/T 12969.2.

4.11 Surface quality shall be inspected visually and using gauges with appropriate accuracy. Surface roughness shall be inspected using a standard block comparison method.

5. Inspection and Acceptance Rules

5.1 Inspection and acceptance:

• 1.1 The supplier shall inspect the products to ensure their quality complies with this standard and the requirements of the purchase order (or contract), and shall issue a quality certificate.
• 1.2 The purchaser shall inspect the received products according to this standard and the requirements of the purchase order (or contract). If the inspection results do not conform to the requirements of this standard and the purchase order (or contract), the purchaser shall notify the supplier within 3 months from the date of receipt, and both parties shall resolve the issue through negotiation.

5.2 Grouping and batching:

• Products shall be submitted for acceptance in batches, with each batch composed of tubing of the same grade, melting furnace batch number, specification, manufacturing method, condition, and from the same heat treatment batch.

5.3 Inspection items and sampling:

• The inspection items and sampling shall comply with the provisions of Table 6.

Table 6: Inspection Items and Sampling

Inspection Item	Sampling Requirements
Chemical composition	Hydrogen content: analyze 1 sample taken from the product. Other elements: supplier reports based on original ingot analysis; if rechecking is required, it should be done on the product.
Dimensional measurements and allowable deviations	Each piece
Mechanical performance	A batch of 2 pieces, 1 sample per piece taken from each batch
Flaring test	A batch of 2 pieces, 1 sample per piece taken from each batch
Flattening test	A batch of 2 pieces, 1 sample per piece taken from each batch
Bend test	A batch of 2 pieces, 1 sample per piece taken from each batch
Hydraulic test	Each piece
Surface contamination	Each piece
Non-destructive testing	Each piece
Ultrasonic testing	Each piece
Eddy current testing	Each piece
Surface quality	Each piece

Note: When the inner diameter of the tubing is not greater than 4mm, 5 pieces per batch shall be sampled, with one test blank sample taken from each piece with a length not less than 150mm. The test blank sample shall be longitudinally cut into two halves to inspect wall thickness and surface quality, and the inspection results represent the batch’s inspection results.

5.4 Determination of Inspection Results

5.4.1 If the chemical composition inspection result is non-compliant, a repeat inspection of the non-compliant element is allowed. If the repeat inspection still fails, the batch of products shall be judged as non-compliant.

5.4.2 For dimensional measurements and allowable deviations, hydraulic testing, non-destructive testing, and surface quality inspection results that are non-compliant, the individual product shall be judged as non-compliant.

5.4.3 For mechanical performance, flaring test, flattening test, bend test, and surface contamination inspection results that are non-compliant, twice the number of samples shall be taken from the batch of products (including the originally non-compliant products) for a repeat inspection of the non-compliant item. If all repeat inspection results are compliant, the batch of products shall be judged as compliant. If any of the repeat inspection results are non-compliant, the batch of products shall be judged as non-compliant. However, the supplier is allowed to inspect each piece individually for non-compliant items; compliant pieces can be re-grouped.

6. Marking, Packaging, Transportation, Storage, and Quality Certificate

6.1 Packaging, Marking, Transportation, and Storage:

• The packaging, marking, transportation, and storage of products shall comply with the provisions of GB/T 8180.

6.2 Quality Certificate:

• Each batch of products shall be accompanied by a quality certificate, which shall indicate: a) Supplier’s name; b) Product name; c) Grade, specification, and condition of the product; d) Melting furnace batch number, batch number, net weight, and quantity; e) Results of various analysis tests and quality inspection department stamp; f) This standard number; g) Packaging date.

7. Purchase Order (or Contract) Content

For orders (or contracts) of products listed in this standard, the following contents shall be included:

• a) Product name;
• b) Grade;
• c) Specification;
• d) Condition;
• e) Net weight and quantity;
• f) This standard number;
• g) Other requirements.