What are the differences in mechanical properties between Q235B and X60 steel welded pipes?
Q235B is a low carbon steel with a yield strength of about 235MPa. It has good plasticity but low strength and is suitable for low-pressure structural pipes; X60 is a pipeline steel with a yield strength of ≥415MPa and contains trace alloying elements (such as Nb, V), with better tensile strength and low-temperature toughness. X60 welding requires preheating to prevent cold cracks, while Q235B weldability is simpler. X60 is 30%-50% higher in cost than Q235B.
Why are stainless steel welded pipes more corrosion-resistant? What are its common grades?
Stainless steel contains chromium (≥10.5%) to form a passivation film to prevent oxidation reactions. 304 (0Cr18Ni9) is resistant to general corrosion, and 316 (0Cr17Ni12Mo2) is resistant to chloride ion corrosion due to the addition of molybdenum. Dual-phase steel (such as 2205) has the advantages of both austenite and ferrite and is resistant to stress corrosion. Stainless steel welded pipes need to control heat input to avoid carbide precipitation.
What is the difference in life between galvanized welded pipes and ordinary carbon steel welded pipes?
The galvanized layer (zinc-iron alloy) protects the substrate through sacrificial anodes, and its life is 3-5 times longer than that of ordinary carbon steel pipes. When the thickness of the galvanized layer is ≥40μm, the outdoor service life can reach 20 years. Ordinary carbon steel pipes need to be regularly coated with anti-corrosion paint, while galvanized pipes are maintenance-free. However, the coating needs to be removed when galvanized pipes are welded, otherwise pores are easily generated.
What special requirements must welded pipe materials meet in low-temperature environments?
Low-temperature pipes (such as L245N) must pass the Charpy V-notch impact test (-40℃ impact energy ≥27J) to ensure that the brittle transition temperature is lower than the use temperature. Grain refinement (such as normalizing treatment) and reducing sulfur and phosphorus content are key. In addition, 100% non-destructive testing of welds is required to prevent defects from becoming crack sources.
How to select welded pipe lining materials based on medium characteristics?
For acidic media (such as H₂S), hydrogen-induced crack (HIC)-resistant steel should be selected, with a hardness of ≤22HRC; for wear-resistant conditions, ceramic or polyurethane lining can be used; for food-grade pipes, 304 stainless steel or aluminum-magnesium alloy should be used. The lining material should match the expansion coefficient of the base pipe to prevent temperature difference peeling.
