Q1: What are the cutting and processing methods of Q235C steel pipe?
Q235C steel pipe can be cut by a variety of methods, including flame cutting, plasma cutting, sawing and laser cutting. Flame cutting is the most commonly used method and is suitable for thicker steel pipes, but the cutting surface is rough and requires subsequent grinding. Plasma cutting has higher precision and is suitable for thin-walled pipes and medium-thick wall pipes. The cutting speed is 2-3 times faster than flame cutting. Sawing is suitable for small batch processing and can ensure high dimensional accuracy, but the efficiency is low. Laser cutting has the highest precision, up to ±0.1mm, but the equipment cost is high and it is suitable for large-scale precision processing. Regardless of the method used, burrs should be removed after cutting, and the quality of the cut should be checked to ensure that there are no cracks and deformations.
Q2: How to choose the connection method (welding/flange/thread) of Q235C steel pipe?
The connection method of Q235C steel pipe needs to be selected according to the use pressure, disassembly frequency and sealing requirements. Welded connections have the highest strength and are suitable for high-pressure, permanent connections, but they cannot be disassembled and require professional welders to operate. Flange connections are easy to disassemble and repair and are suitable for medium and high-pressure pipeline systems, but they are more expensive and take up a lot of space. Threaded connections are simple and convenient and are suitable for low-pressure, small-diameter pipelines, but they have poor sealing and need to be used with sealing tape. For pipeline systems that require frequent maintenance, flange connections are recommended; for permanent structural parts, welding connections are preferred. Clamp connections or flared connections can also be used in special occasions, but it is necessary to ensure that the strength of the joints meets the requirements.
Q3: How to prevent rust when Q235C steel pipes are used outdoors?
Effective anti-rust measures must be taken when Q235C steel pipes are used outdoors, including hot-dip galvanizing, spraying anti-rust paint, and cathodic protection. Hot-dip galvanizing is the most reliable anti-rust method, and the zinc layer thickness is usually 60-80μm, which can provide a protection period of more than 10 years. Spraying anti-rust paint has a low cost and is easy to construct, but it requires regular maintenance and generally needs to be repainted every 3-5 years. Cathodic protection is suitable for buried pipelines or marine environments, and it delays corrosion by sacrificial anodes or impressed currents. For temporary structures, anti-rust oil or anti-rust wax can be used for short-term protection. Regardless of the method used, the surface of the steel pipe must be thoroughly cleaned before construction to remove oil and scale to ensure that the protective layer is firmly attached.
Q4: How to evaluate the fatigue life of Q235C steel pipes?
To evaluate the fatigue life of Q235C steel pipes, factors such as load type, stress amplitude, number of cycles and surface state need to be considered. First, the alternating stress amplitude to which the steel pipe is subjected should be determined by stress analysis, and then fatigue tests should be carried out in accordance with standards such as GB/T 3075. The fatigue limit of Q235C steel is about 40-50% of the tensile strength, that is, it can withstand 10^7 cycles at a stress amplitude of 200-250MPa. In practical applications, it is recommended to use a safety factor of 2-3 to control the working stress below 100MPa. Surface treatment such as shot peening can increase the fatigue life by 20-30%, while the fatigue strength at the welded joint is usually only 70% of the parent material. For key components, non-destructive testing should be carried out regularly to detect fatigue cracks in time.
Q5: What are the protective measures for Q235C steel pipes in corrosive environments?
Multiple protective measures are required when using Q235C steel pipes in corrosive environments. For chemical corrosion environments, corrosion-resistant coatings such as epoxy coal tar, polyurethane or fluorocarbon coatings can be selected, and the coating thickness should reach 200-300μm. For electrochemical corrosion environments, cathodic protection should be used in combination with anti-corrosion coatings, and the protection potential should be controlled at -0.85～-1.05V (relative to Cu/CuSO4 electrodes). For acidic media, plastic or rubber can be lined inside the steel pipe, such as PP, PVC or fluororubber. In atmospheric corrosion environments, hot-dip galvanizing combined with sealants is the best. For particularly harsh environments, stainless steel pipes or fiberglass pipes should be considered. Regardless of the protective measures adopted, the condition of the protective layer should be checked regularly and damaged parts should be repaired in time.
