Simplified main production processes for stainless steel seamless pipes: Round steel → Re-inspection → Peeling → Blanking → Centering → Heating → Piercing → Pickling → End finishing → Inspection and grinding → Cold rolling (cold drawing) → Degreasing → Heat treatment → Straightening → Pipe cutting (to length) → Pickling/passivation → Finished product inspection (eddy current, ultrasonic, hydrostatic) → Packaging and warehousing.
1. Round steel cutting: After receiving round steel from the raw material warehouse, calculate the cutting length according to the process requirements. Mark the sections on the round steel. After starting the bow-shaped saw, the grinding wheel cuts along the section lines. The cut round steel is stacked according to steel type, furnace number, production batch number, and specifications. The ends are distinguished by different colors of paint.
2. Centering: When centering with a horizontal arm drilling machine, first find the center point on one section of the round steel, drill a sample hole, and then fix it vertically on the drilling machine’s worktable for centering. After centering, the round steel bars are stacked according to steel type, furnace number, specifications, and production batch number.
3. Peeling: After the incoming material passes inspection, peeling is performed. Peeling includes lathe peeling and cyclone cutting. Lathe peeling is done on a lathe using a clamping and lifting method. Cyclone cutting involves hoisting the round steel bar onto a machine tool for cyclone cutting.
4. Surface Inspection: The peeled, clean round steel bars undergo quality inspection. Any surface defects are marked, and the grinding personnel grind them until they meet the requirements. The inspected and qualified round steel bars are stacked according to steel type, furnace number, specifications, and production batch number.
5. Round Steel Heating: The round steel heating equipment includes gas-fired inclined hearth furnaces and gas-fired box furnaces. Gas-fired inclined hearth furnaces are used for large batches of incoming material, while gas-fired box furnaces are used for small batches.
6. Hot Rolling Piercing: A piercing mill and air compressor are used. Based on the specifications of the round steel, corresponding guide plates and molybdenum mandrels are selected. The heated round steel is pierced using the piercing mill, and the resulting rough tubes are randomly immersed in a water tank for thorough cooling.
7. Inspection and Grinding: The inner and outer surfaces of the rough tubes are inspected for smoothness and flatness, free from defects such as blemishes, cracks, delamination, deep pits, severe thread marks, tower iron marks, oil-strip shapes, wrapped ends, and sickle-shaped ends. Surface defects can be eliminated through localized grinding. Rough tubes that pass inspection or those with minor defects that pass inspection after grinding are bundled by workshop workers according to requirements and stacked separately according to their steel grade, heat number, specifications, and production batch number. 8. Straightening: Incoming raw tubes from the piercing workshop are packaged in bundles. The incoming raw tubes are curved and need to be straightened. Straightening equipment includes vertical straightening machines, horizontal straightening machines, and vertical hydraulic presses (used for pre-straightening when the stainless steel seamless tubes have large curvature). To prevent the stainless steel seamless tubes from jumping during straightening, nylon sleeves are used to restrain them.
9. Cutting: According to the production plan, the straightened raw tubes need to be cut at the beginning and end using an abrasive wheel cutter.
10. Pickling: The straightened stainless steel seamless tubes need to be pickled to remove oxide scale and impurities from the surface. Pickling is carried out in the pickling workshop. A crane slowly lowers the stainless steel seamless tubes into the pickling tank for pickling. After pickling, the stainless steel seamless tubes are first rinsed in a water washing tank, and then each tube is rinsed individually with high-pressure clean water, both inside and outside.
11. Grinding, Endoscopic Inspection, and Internal Polishing: Stainless steel seamless tubes that pass the pickling process proceed to the outer surface grinding process. After grinding, the tubes undergo endoscopic inspection. Those failing inspection or requiring special processes require internal polishing.
12. Cold Rolling/Cold Drawing Process
(1) Cold Rolling: Stainless steel seamless tubes are rolled by the rolls of a cold rolling mill, undergoing continuous cold deformation to change their size and length. Cold-rolled stainless steel seamless tubes have a faster forming speed, larger deformation, and higher output.
(2) Cold Drawing: Stainless steel seamless tubes are expanded and have their wall thickness reduced using a cold drawing machine without heating to change their size and length. Cold-drawn stainless steel seamless tubes have high dimensional accuracy and good surface finish. The disadvantages are higher residual stress, more frequent cold drawing of large-diameter tubes, and slower finished product forming speed. The specific steps of cold drawing include:
① Heading and Welding: Before cold drawing, one end of the stainless steel seamless tube needs to be headed (for small-diameter stainless steel seamless tubes) or welded (for large-diameter stainless steel seamless tubes) to prepare for the drawing process. For a small quantity of special specification stainless steel seamless tubes, heating is required before heading.
② Lubrication and Baking: Before cold drawing, the inner hole and outer surface of the headed (welded) stainless steel seamless tube need to be lubricated. The lubricated stainless steel seamless tube must be dried before cold drawing.
③ Cold Drawing: After the lubricant has dried, the stainless steel seamless tube enters the cold drawing process. The equipment used for cold drawing is a chain cold drawing machine and a hydraulic cold drawing machine.
13. Degreasing: The purpose of degreasing is to remove the rolling mill oil adhering to the inner wall and outer surface of the stainless steel seamless tube after rolling by rinsing, to prevent contamination of the steel surface during annealing and to prevent carbon buildup.
14. Heat Treatment: Heat treatment restores the material’s plasticity through recrystallization and reduces the metal’s resistance to deformation. The heat treatment equipment is a natural gas solution heat treatment furnace. 15. Finished Product Pickling: After cutting, the seamless stainless steel tubes undergo pickling to passivate the surface, forming a protective oxide film that enhances their corrosion resistance.
16. Finished Product Inspection: The inspection and testing process mainly involves surface inspection → eddy current testing → ultrasonic testing → hydrostatic testing → air pressure testing. Surface inspection primarily involves manual inspection of the seamless stainless steel tube surface for defects and checking the length and outer wall dimensions for compliance. Eddy current testing uses an eddy current flaw detector to check for leaks. Ultrasonic testing uses an ultrasonic flaw detector to check for internal and external cracks. Hydrostatic and air pressure tests use hydraulic and air pressure machines to check for leaks, ensuring the tubes are in good condition.
Packaging and Warehousing: Qualified seamless stainless steel tubes are packaged in the finished product packaging area. Packaging materials include perforated caps, plastic bags, tarpaulins, wooden boards, and stainless steel strips. The wrapped stainless steel seamless pipes are padded with small wooden boards at both ends and secured with stainless steel straps to prevent contact and collisions between the pipes during transportation. The packaged stainless steel seamless pipes are then moved to the finished product storage area.
Post time: May-12-2026