I. Acceptance of Raw Materials

1. Raw materials shall meet the requirements of relevant standards and 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 plates).

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

7. Physical and chemical testing: The steel plates entering the factory shall undergo chemical element analysis, mechanical property tests, and hardness tests according to furnace batch number and specification. The test results must meet the requirements of the raw material standards.

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

II. Manufacturing Process

(1) Hot pressing and molding

1. For material selection and cutting, choose appropriate steel plates (rolled into tube blanks, then mechanically beveled and corrected) or steel pipes according to the specifications of the tee fittings. Use a semi-automatic oxy-acetylene flame or plasma cutting for cutting. Clearly mark the furnace number, batch number, pipe fitting specifications, project name, and identification number on the raw materials.

2. Three-way compression molding

① Operators should study the relevant process documents and become familiar with the equipment’s operating procedures and process flow, and also prepare all necessary tools and instruments for use during the work.

② Furnace Loading and Heating: Place the tee billets into the natural gas heat treatment furnace. Use spacer blocks at the bottom to isolate the billets from the furnace car, ensuring that the spacing between tees is ≥200 mm. The heating rate above 400℃ shall be ≤200℃/h.

③ Heat and hold the tee blank to ensure it is thoroughly heated through, then remove it from the furnace and flatten it (making sure the weld seam is located at the center of the tee). After flattening, the length of the short axis should not exceed the outer diameter of the tee (i.e., the inner diameter of the die).

④ Continue loading the furnace, heating it up, and maintaining the temperature. After removing the billet from the furnace, quench the three-way pipe blank (with the weld seam at the bottom), then quickly place the billet into the mold to form a bulge. Under pressure, the uncooled portion flows along the inner cavity of the mandrel, thereby forming the branch pipe.

⑤ Repeat process ④ until the branch pipe meets the requirements.

⑥ Hole Cutting: Using the bottom of the tee as the reference point, measure a certain distance toward the branch pipe; then, using the shoulder of the main pipe as the reference point, measure another certain distance toward the branch pipe. Mark the points and connect them with a cutting torch to create the hole.

⑦ After further heating and holding the tee blank, quench the main pipe section in water and then quickly place the tee into the mold. Insert the drawing die into the branch pipe and use a press to push it down—during the pressing process, the drawing die must be pressed straight down to ensure that the branch pipe is not skewed—until the branch pipe meets the required specifications.

⑧ End trimming: Using the center of the branch pipe as the reference point, measure a specified distance toward the end of the main pipe; using the bottom of the tee as the reference point, measure a specified distance toward the branch pipe, and remove the excess portion with a cutting torch.

⑨ Forming: Reheat the tee, then use a press to round out the main and branch pipes of the tee.

6. Heat Treatment: Place the tee into the furnace and perform heat treatment according to the specified heat treatment process.

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

8. After surface treatment, perform 100% radiographic inspection on the tee welds; the welds shall meet Grade II acceptance criteria. Perform 100% magnetic particle or penetrant testing on the body of the pipe fittings; the results shall comply with the Grade I requirements specified in NB/T47013.4-2015 or NB/T47013.5-2015.

9. Mechanical Performance Testing: Conduct mechanical performance tests on the tee fittings according to relevant standards to ensure that their mechanical performance meets the specified requirements. The testing items and sampling locations shall comply with the requirements of the relevant standards or technical specifications.

10. 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 reinforcement from both the inner and outer weld seams.

11. Visual Inspection

① The three-way fitting must not exhibit cracks, overburning, overheating, or similar defects; its surface should be free of hard spots.

② The root of the three-way branch pipe must not have any obvious wrinkles.

③ Any defects on the three-way pipe body are not permitted to be repaired by welding.

12. Dimensional Inspection

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

13. Surface Treatment: The inner and outer surfaces of the tee 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 to remove the flaws. 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.

14. Pickling and Passivation Treatment

Stainless steel pipe fittings should also undergo pickling and passivation treatment.

15. Labeling

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

16. Stacking and transportation of three-way valves

During transportation, the three-way valve must not come into contact with any part of the vehicle body to avoid impacts.