I. Acceptance of Raw Materials

1. Raw materials shall meet the requirements of relevant standards or technical specifications.

2. The surface of the raw materials should be free of oil stains, excessive rust and corrosion, obvious dents or defects, and contamination by low-melting-point metals.

3. Verify the certificates of material quality, furnace number, batch number, specifications, manufacturer, and applicable standards.

4. The raw materials shall be mechanically descaled using a steel wire brush to meet the requirements for non-destructive testing.

5. Perform dimensional inspections on raw materials (length, width, thickness, and flatness of steel pipes).

6. After entering the factory, steel pipes and steel plates shall undergo ultrasonic re-inspection; Grade I is considered qualified.

7. Physical and chemical testing: Steel pipes and steel plates entering the plant shall be sampled according to furnace batch number and specification for chemical element analysis, mechanical property testing, and hardness testing. The test results must meet the requirements of the raw material standards.

8. After re-inspection, assign a number and register it according to the company’s regulations.

II. Manufacturing Process

① Material selection and cutting: Choose appropriate steel plates or steel pipes for bending. Use templates to mark lines, then cut the materials using an oxy-acetylene flame or a sawing machine. Clearly label the furnace batch number, material specifications, project name, and identification number on the raw materials.

② Coil and weld the steel plates.

③ Use a crane to load the required mandrels into the push-forming machine. Further clean the billet thoroughly and coat its inner wall with graphite. Then, mount the billet onto the push rod (multiple billets can be loaded at once, depending on their length). Secure the mandrel with a locking plate, and preheat the inner die to an appropriate temperature before starting the push-forming process. The heating temperature and pushing speed should be optimally matched.

④ Adjust the intermediate-frequency heating coil to heat the tube billet to the required temperature, and control the advancement speed.

⑤ Remove the burr. Using appropriate fixtures on the beveling machine, align the pipe according to its specifications. Then securely fasten the cutting torch, cut off the excess stock, and leave sufficient machining allowance for the pipe end.

⑥ For tube shaping, clamp the bent pipe securely using a specialized fixture and perform end-forming on a press using a mandrel.

4. Heat Treatment: According to the heat treatment process, place the bent pipe into the furnace for heat treatment.

5. Surface Treatment: After heat treatment, the pipe fittings are cleaned of surface scale using a sandblasting machine.

6. After surface treatment, the weld seams of the elbow shall undergo 100% radiographic inspection and meet Grade II acceptance criteria.

7. Mechanical Performance Testing: Conduct mechanical performance tests on elbows according to relevant standards to ensure that their mechanical properties meet the specified requirements. The testing items and sampling locations shall comply with the provisions of the relevant standards.

8. End machining: Perform mechanical end-face beveling according to the drawings confirmed by the design. Within 50 mm of the pipe end, use an angle grinder to remove any excess weld metal from both the inner and outer weld seams.

9. Visual Inspection

① The bent pipe shall not have any cracks or other defects, and its surface shall be free of hard spots.

② Any defects on the pipe body of the bent pipe are not allowed to be repaired by welding.

10. Dimensional Inspection: Relevant inspection personnel from the company shall conduct dimensional inspections based on the drawings and the relevant standard requirements for pipe fittings, ensuring that the dimensions meet the specified tolerance requirements.

11. Surface Treatment: The inner and outer surfaces of the bent pipe shall be smooth and free from defects that could compromise strength or appearance, such as knots, scratches, or laps. Upon detection of any defects, they shall be ground down. The thickness reduction at the ground areas shall be no less than 93.5% of the original wall thickness. The ground areas shall be smoothly rounded, and their defect-free status shall be confirmed by means of dye penetrant testing or magnetic particle inspection until no defects remain.

12. Nondestructive Testing of Elbows

After heat treatment of the bent pipe, personnel holding the relevant qualification certificates from the company performed magnetic particle and ultrasonic inspections on the bent pipe according to standard requirements, and the inspection results met Grade I acceptance criteria.

13. Label

Mark using a template spray or low-stress impression, clearly indicating the content required by standards in sequential order on the outer wall.

14. Stacking and Transportation of Elbows

During transportation, the bent pipe must not come into contact with any part of the vehicle’s interior to avoid impacts and collisions.