Carbon steel pipes have excellent flexibility, corrosion resistance, heat resistance, wear resistance, compressive strength, water resistance and excellent magnetic shielding properties. Carbon steel tube capillaries can be deformed into various angles and angles at will, and have the same flexibility and durability in all directions. The carbon steel pipe is flexible, has good toughness, no obstruction and bending stiffness; the carbon steel pipe has a certain tensile strength between the side buckles to prevent the plastic hose from being damaged due to the damage of the plastic hose. The radial tensile strength can withstand more than 6 times the tolerance of the inner diameter. Therefore, the installation of carbon steel pipe capillaries is convenient, and low-efficiency energy can be used effectively to achieve environmental protection and energy-saving effects.
Annealing process of carbon steel pipes
Annealing is a heat treatment process to improve the performance of carbon steel pipes. The following is its general process:
Preparation before annealing
1. Steel pipe inspection: Conduct a comprehensive inspection of carbon steel pipes that need to be annealed, including dimensional measurement, appearance inspection, etc. Confirm that the specifications and models of the steel pipes meet the requirements, and there are no obvious cracks, scratches, deformations and other defects on the surface. For defective steel pipes, it is necessary to evaluate their impact on the annealing process and results, and repair or remove them if necessary.
2. Equipment preparation: Select a suitable annealing furnace according to the material, size and annealing process requirements of the carbon steel pipe. Common annealing furnaces include box-type furnaces, pit-type furnaces, etc. Check whether the heating system, temperature control system, ventilation system, etc. of the annealing furnace are operating normally to ensure that the furnace temperature uniformity and control accuracy meet the annealing requirements. At the same time, prepare auxiliary tools such as temperature measuring instruments (such as thermocouples) and charging fixtures.
3. Furnace loading: Load the carbon steel pipes into the annealing furnace properly. When loading, pay attention to maintaining a certain gap between the steel pipes to avoid mutual squeezing and collision to ensure uniform heating. For large-diameter or special-shaped carbon steel pipes, special furnace loading methods or support fixtures may be required to ensure their stability in the furnace.
Heating stage
1. Heating: Start heating at the predetermined heating rate. The heating rate is usually determined by factors such as the material, size and furnace type of the carbon steel pipe. Generally speaking, for large-diameter or thick-walled carbon steel pipes, the heating speed should not be too fast to avoid excessive thermal stress that may cause deformation or cracking of the steel pipe. For example, for medium carbon steel seamless pipes with thicker wall thickness, the heating rate can be controlled at 50 - 100℃/h; for small diameter thin-walled steel pipes, the heating rate can be appropriately increased to 100 - 200℃/h.
2. Reach annealing temperature: When the furnace temperature rises to the predetermined annealing temperature, start to keep warm. The annealing temperature varies with different annealing processes and carbon steel pipe materials. For example, during complete annealing, the heating temperature of medium carbon steel is generally 30-50℃ above Ac3 (austenitizing critical temperature); the heating temperature of incomplete annealing is between Ac1 (lower critical point) and Ac3; the stress relief annealing temperature is generally between 500-650℃.
Insulation stage
The holding time is determined according to the wall thickness of the carbon steel pipe. The general principle is to hold the pipe for 1 to 4 minutes per millimeter of wall thickness, but the total holding time should not be less than 30 minutes. For example, for a carbon steel pipe with a wall thickness of 20 mm, if full annealing is used, the holding time should be 20 to 80 minutes. During the holding process, the furnace temperature must be kept stable, and the heating power must be adjusted in time through the temperature control system to keep the furnace temperature within the set annealing temperature range.
Cooling phase
1. Cooling with the furnace: After the insulation is completed, cooling begins. For complete annealing and spheroidizing annealing, the cooling with the furnace is usually adopted, and the cooling speed is relatively slow. Generally controlled at 20-50℃/h to ensure that the internal structure of the steel pipe is fully transformed and the stress is eliminated. When the steel pipe is cooled to a certain temperature (such as 500-600℃), for some situations with low requirements, it can be taken out of the furnace for air cooling.
2. Control cooling speed: For incomplete annealing and stress relief annealing, the cooling speed can be appropriately accelerated according to the specific situation, but it still needs to be controlled within a certain range. For example, incomplete annealing can be cooled to 550-650℃ in the furnace at a speed of 30-70℃/h, and then air-cooled; stress relief annealing is usually cooled to below 400℃ in the furnace at a speed of 20-50℃/h, and then air-cooled.
Annealing post-treatment
1. Inspection after leaving the furnace: After the carbon steel pipe cools to room temperature, it is taken out of the annealing furnace. The appearance of the steel pipe is inspected again to check whether there are any defects such as deformation and cracking caused by the annealing process. At the same time, the size of the steel pipe is measured to check whether it meets the requirements.
2. Performance testing: According to the needs, the annealed carbon steel pipe is tested for performance, such as hardness test, metallographic analysis, mechanical property test (tensile test, impact test, etc.). Through these tests, the improvement effect of annealing process on steel pipe performance is evaluated to determine whether the expected annealing purpose is achieved.
3. Marking and recording: Qualified carbon steel pipes are marked with information such as material, specification, annealing process parameters, etc. At the same time, various data during the annealing process are recorded in detail, including heating speed, annealing temperature, holding time, cooling method, etc., for subsequent inquiries and quality traceability.
Read more：Applications of Carbon Steel Pipes in Pipeline Engineering
