1. Raw material cutting and trimming Select seamless steel pipes and bar stock materials, according to the ordered length dimensions. Use sawing machines and cutting machines to precisely cut the raw materials, remove burrs at the pipe ends, ensure that the length tolerance meets the standards, select qualified raw materials with acceptable wall thickness and outer diameter, and eliminate defective products with cracks and uneven wall thickness.
2. Outer circle and end face finishing
Mount the raw materials on the lathe, precisely machine the outer diameter of the pipe body, and smooth both ends of the end faces. Ensure that the end faces are perpendicular and smooth, laying the foundation for subsequent thread machining and welding grooves. Control the roundness and coaxiality to avoid subsequent thread eccentricity.
3. Precision thread machining
According to NPT/BSP and other standard parameters, machine the external conical threads or straight threads on the lathe. Strictly control the tooth profile angle, pitch, and taper. After processing, use the corresponding thread gauge for pass and stop detection to ensure the tightness of the threads and the qualification of the sealing performance.
4. Groove processing (single-head short section)
Process the non-threaded end of the single-head short section into a welding groove, machine a V-shaped groove, and smooth the groove surface to facilitate subsequent welding integration with the pipeline; both ends of the double-head short section are machined with threads, omitting the groove processing procedure.
5. Grinding, cleaning, and flaw detection
Overall grind off burrs and machining chips, conduct visual inspection and magnetic particle or penetrant flaw detection for products under high-pressure conditions to identify defects such as thread roots, pipe wall cracks, and sand holes.
6. Surface treatment and final inspection
For carbon steel, perform blackening and galvanizing anti-rust treatment; for stainless steel, do acid washing and passivation. Finally, recheck the specifications, thread accuracy, dimensions, and pressure-bearing grade. Qualified products are labeled and stored, while non-qualified products are reworked or scrapped.