1. Process Overview
Steel pipe annealing is a necessary heat treatment process for mechanical engineering pipes, seamless pipes, alloy pipes and structural pipes. The annealing heating equipment (medium-frequency induction annealing furnace, continuous roller hearth annealing furnace) heats the steel pipe to a fixed temperature, keeps uniform temperature, and cools down slowly. This process removes internal stress generated by rolling, cold drawing, forging and welding, reduces hardness, improves plasticity and toughness, refines metal grain structure, and makes the pipe suitable for bending, expanding, cutting and further mechanical processing.
2. Application ScopeApplicable to carbon steel, alloy steel, low-alloy structural steel, and mechanical engineering special steel pipes. Suitable for all pipe diameters and wall thicknesses. Used for batch production and continuous online annealing production.
3. Working Principle of Annealing Heating Equipment
The heating equipment uses medium-frequency induction heating or resistance heating to heat the pipe evenly from inner wall to outer wall. After reaching the set annealing temperature, the pipe is kept at constant temperature to stabilize the metallographic structure. Then slow cooling is carried out to avoid new stress and deformation. Finally, the steel pipe obtains stable mechanical performance and soft material condition.
steel pipe induction annealing furnace
4. Main Annealing Types Used in Pipe Production
4.1 Stress Relief AnnealingUsed for cold-drawn pipes, welded pipes and forged pipe parts. Heating temperature: 550℃–650℃. Main function: remove residual stress, prevent later cracking and deformation.
4.2 Full AnnealingUsed for medium carbon steel and alloy steel pipes. Heating temperature: 750℃–850℃. Refines grain, uniformizes internal structure, improves toughness.
4.3 Spheroidizing AnnealingUsed for high-carbon steel pipes. Reduce hardness for easy machining and cutting.
4.4 Bright AnnealingWith nitrogen protective atmosphere, no oxidation on pipe surface, smooth surface without black oxide scale.
5. Complete Standard Operation Process (Production Line Steps)
Step 1 Preparation before heatingCheck the annealing heating equipment, cooling water system, power supply, temperature control system and conveyor roller table. Clean oil, rust and dirt on the steel pipe surface. Classify pipes by material and wall thickness to avoid mixing materials.
Step 2 Feeding and conveyingPut steel pipes on the automatic roller table steadily. Keep uniform feeding speed to ensure no shaking, no collision and no bending during heating.
Step 3 Preheating sectionSlowly heat the pipe to avoid temperature difference between inner and outer wall. Prevent pipe deformation and cracking caused by rapid heating.
Step 4 Main constant temperature heating sectionThe induction heating coil heats the pipe to the standard annealing temperature. The equipment ensures uniform heating on the whole pipe wall, no local overheating, no under-heating.
Step 5 Soaking and holding timeKeep constant temperature according to pipe wall thickness. Thicker wall needs longer holding time. Ensure complete stress relief and stable metallographic structure.
Step 6 Slow cooling processCool down slowly inside the furnace or cooling chamber. Strictly forbid rapid water cooling. Control cooling speed steadily to keep good toughness and straight pipe shape.
Step 7 Discharging and quality inspectionCheck pipe straightness, surface quality, hardness and internal structure. Qualified pipes are stacked and stored; unqualified pipes will be re-annealed.
6. Core Technical Parameters (Key Data for Machine Setting)
Heating temperature: 550℃–850℃ (according to steel grade)
Temperature control accuracy: ±5℃
Heating speed: 100℃–200℃ per hour
Holding time: 1–3 minutes per 1mm wall thickness
Cooling speed: 50℃–100℃ per hour (slow cooling)
Working power: medium frequency induction power matched with pipe diameter
Water cooling pressure: stable circulating water for heating coil protection
7. Safety and Equipment Operation Rules
1. Do not overheat the equipment beyond the limit temperature.
2. Keep cooling water circulation normal to protect induction coils.
3. No fire, no flammable materials near the heating furnace.
4. Check electrical parts regularly to avoid electric leakage.
5. Clean oxide scale on rollers and furnace body every day to ensure stable heating effect.
6. Operators must wear high-temperature protective gloves and safety clothes.
8. Finished Quality Standard after Annealing
- No pipe bending, no deformation, no cracking.
- No oxidation skin, no black surface (for bright annealing).
- Hardness uniform, easy for further forging, turning and bending.
- Internal stress completely removed.
- Metallographic grain uniform and fine.
9. Advantages of This Annealing Equipment Process
- Fast heating, low energy consumption, high efficiency.
- Uniform heating inside and outside the pipe.
- Small deformation, high finished product rate.
- Suitable for mass automatic production line.
- Simple operation, stable running, low maintenance cost.
pipe induction annealing machine
