1. Question: Why is 20# steel pipe one of the most widely used high-quality carbon structural steel pipes in industry? What are its main application scenarios?
Answer: The core reason why 20# steel pipe has become a widely used high-quality carbon structural steel pipe in industry is its balanced mechanical properties (moderate strength, good plasticity and toughness), excellent processing performance (good welding, cutting, and forming performance), low impurity content, stable performance, and moderate price, balancing performance and cost. Its main application scenarios include: 1. Fluid transportation pipelines: such as pipelines transporting oil, natural gas, and steam (pressure 1.6-4.0MPa), capable of withstanding certain pressure and possessing good toughness, making it less prone to breakage due to media impact; 2. Machining parts: such as shafts, sleeves, gear blanks, connecting rods, etc., whose strength can be improved through heat treatment to meet the usage requirements of mechanical parts; 3. Welded structural components: such as welded frames of engineering machinery and structural components of automobile chassis, with good welding performance to ensure structural stability; 4. Pressure vessels: such as the shells of small pressure vessels, with good plasticity and toughness, capable of withstanding certain pressure and impact.
2. Question: Can Q255 and Q275 steel pipes be used to transport corrosive media? Why? If they must be used, what measures should be taken?
Answer: Q255 and Q275 steel pipes are not suitable for long-term transport of corrosive media (such as acids, alkalis, salt solutions, seawater, etc.) because they are ordinary carbon structural steels without rust prevention or corrosion resistance. Long-term contact with corrosive media will cause oxidation corrosion, leading to thinning of the pipe wall, decreased strength, and ultimately leakage or breakage. If Q255 and Q275 steel pipes must be used to transport corrosive media, the following anti-corrosion measures should be taken: 1. Apply anti-corrosion treatment to the steel pipe surface, such as galvanizing (hot-dip galvanizing, cold galvanizing) or applying anti-corrosion coatings (epoxy coal tar pitch, polyurethane coatings) to isolate the medium from the steel pipe surface; 2. Regularly inspect and maintain the steel pipes, and promptly repair any damaged anti-corrosion layers; 3. Add corrosion inhibitors to the medium to slow down the corrosion rate, but this method is only suitable for weakly corrosive media.
3. Question: What are the differences in the applications of 10# and 20# steel pipes in the machining field? What types of mechanical parts are they respectively suitable for manufacturing?
Answer: The difference in the applications of 10# and 20# steel pipes in the machining field mainly stems from the differences in their strength and plasticity: 10# steel pipes have low strength and good plasticity, making them suitable for manufacturing mechanical parts that do not require high strength but have high requirements for plasticity and formability, such as: stamped parts (gaskets, seals), thin-walled sleeve parts, bent connecting parts, and low-load shaft parts that do not require heat treatment; 20# steel pipes have medium strength and good plasticity, making them suitable for manufacturing mechanical parts that require a balance between strength and plasticity, and whose strength can be improved through heat treatment, such as: gear blanks, connecting rods, medium-load shaft parts (such as machine tool spindles, motor shafts), sleeve parts (such as bearing sleeves), piston pins, etc. After normalizing or quenching and tempering treatment, they can meet the load-bearing requirements of mechanical parts.
V. Identification and Maintenance
4. Question: How to quickly identify Q255, Q275, 10#, and 20# steel pipes? What are some simple and easy methods?
Answer: There are three main methods for quick identification, which are simple, easy to implement, and suitable for on-site operation: 1. Appearance and Marking Identification: High-quality carbon structural steel pipes (10#, 20#) have a smooth surface, no obvious oxide scale, and clear markings, usually indicating the grade, specifications, and manufacturer; ordinary carbon structural steel pipes (Q255, Q275) may have slight oxide scale on the surface, and the markings are relatively simple, often marked with "Q255" or "Q275". 2. Hardness Identification: Measure the hardness with a hardness tester. The hardness from highest to lowest is Q275 > Q255 > 20# > 10#. Scratch the pipe with a hard object (such as a steel nail). The shallower the scratch, the higher the hardness, which can be used for preliminary judgment.
3. Spark Identification: Grind the surface of the steel pipe with a grinding wheel and observe the sparks: 10# steel sparks are fine, with few branches, and a lighter color; 20# steel sparks are slightly coarser than 10# steel, with slightly more branches; Q255 steel sparks are relatively coarse, with many branches, and a small amount of bursting; Q275 steel sparks are the coarsest, with many branches, obvious bursting, and a brighter color.
5. Question: What damage problems are prone to occur in Q255 steel pipes during use? How to perform daily maintenance? Answer: Common damage problems of Q255 steel pipes during use: 1. Corrosion damage: Surface oxidation and rust; long-term exposure to humid and corrosive environments can lead to thinning of the wall thickness; 2. Deformation damage: Excessive load or impact can cause plastic deformation such as bending and denting; 3. Fracture damage: Under low-temperature environments or under long-term fatigue loads, brittle fracture or fatigue fracture can occur. Daily maintenance methods: 1. Regularly clean the rust and oil stains on the surface of the steel pipe, keep the surface dry and clean, and avoid corrosion from humid environments; 2. For steel pipes exposed outdoors, regularly apply anti-corrosion coatings or galvanize to enhance corrosion resistance; 3. Regularly check the stress on the steel pipe, avoid overloading, and replace deformed or damaged steel pipes in time; 4. In low-temperature environments, avoid impact loads on the steel pipe, and perform insulation treatment if necessary.
