Stress relief annealing is a process of heating steel pipes (seamless pipes, welded steel pipes) to an appropriate temperature, and gradually cooling down after holding for a certain period of time. Its purpose is to remove the residual stress of the steel pipe due to machining, deformation processing, casting, forging, heat treatment and welding. If these stresses are not eliminated, it will cause deformation or cracks in the steel pipe after a certain period of time, or in the subsequent cutting process.
Stress Relief Annealing Process
Furnace loading of steel pipe → heating → heat preservation → cooling → steel pipe out of furnace
(1) Furnace loading of steel pipes: Generally, medium and small pipes can be directly loaded into the furnace at the annealing temperature, or can be loaded into the furnace at a low temperature, and the temperature rises with the furnace. When the number of large pipes or steel pipes is large, the furnace is generally charged at low temperature.
(2) Heating and cooling: heating and cooling are carried out according to a certain heating and cooling rate. After the heat preservation is completed, the power (fire) is generally cut off, and the heating is stopped, so that the workpiece is gradually cooled in the furnace.
(3) Holding time: holding time refers to the total time from the time when the furnace instrument reaches the specified annealing heating temperature to when the workpiece stops heating in the furnace and starts to cool down.
(4) Steel pipe out of the furnace: When the steel pipe cools down in the furnace to a certain temperature, it can be released from the furnace for air cooling.
Problems that should be paid attention to in the process of stress relief annealing
1. Equipment:
(1) Whether the heat treatment furnace can meet the requirements of adjustable temperature control;
(2) The heat treatment furnace ammeter and temperature measuring meter have been certified, can be used normally, and are within the period of certification;
(3) Whether the heating system, air circulation system and temperature control system in the furnace can work normally to ensure the temperature balance of the heat treatment furnace;
(4) The heat treatment process must be automatically recorded;
2. Steel pipe
(1) The heat treatment can only be carried out after the heat treatment steel pipe is completed and passed the inspection;
(2) Products that undergo post-weld heat treatment shall not be welded and repaired after heat treatment, otherwise they need to be re-heat treated;
(3) The stacking of materials should be standardized, and tooling should be used for protection when necessary to ensure that the product will not be damaged during the heat treatment process;
(4) Magnetic particle inspection should be carried out after stress removal annealing, so as to ensure that no cracks and other defects are produced on the welding surface after stress release;
(5) Natural aging should be increased after heat treatment of large pieces.
Stress Relief Annealing Process
Furnace loading of steel pipe → heating → heat preservation → cooling → steel pipe out of furnace
(1) Furnace loading of steel pipes: Generally, medium and small pipes can be directly loaded into the furnace at the annealing temperature, or can be loaded into the furnace at a low temperature, and the temperature rises with the furnace. When the number of large pipes or steel pipes is large, the furnace is generally charged at low temperature.
(2) Heating and cooling: heating and cooling are carried out according to a certain heating and cooling rate. After the heat preservation is completed, the power (fire) is generally cut off, and the heating is stopped, so that the workpiece is gradually cooled in the furnace.
(3) Holding time: holding time refers to the total time from the time when the furnace instrument reaches the specified annealing heating temperature to when the workpiece stops heating in the furnace and starts to cool down.
(4) Steel pipe out of the furnace: When the steel pipe cools down in the furnace to a certain temperature, it can be released from the furnace for air cooling.
Problems that should be paid attention to in the process of stress relief annealing
1. Equipment:
(1) Whether the heat treatment furnace can meet the requirements of adjustable temperature control;
(2) The heat treatment furnace ammeter and temperature measuring meter have been certified, can be used normally, and are within the period of certification;
(3) Whether the heating system, air circulation system and temperature control system in the furnace can work normally to ensure the temperature balance of the heat treatment furnace;
(4) The heat treatment process must be automatically recorded;
2. Steel pipe
(1) The heat treatment can only be carried out after the heat treatment steel pipe is completed and passed the inspection;
(2) Products that undergo post-weld heat treatment shall not be welded and repaired after heat treatment, otherwise they need to be re-heat treated;
(3) The stacking of materials should be standardized, and tooling should be used for protection when necessary to ensure that the product will not be damaged during the heat treatment process;
(4) Magnetic particle inspection should be carried out after stress removal annealing, so as to ensure that no cracks and other defects are produced on the welding surface after stress release;
(5) Natural aging should be increased after heat treatment of large pieces.
