Q1: What welding techniques produce Q235B welded pipe?
A1: Three primary methods are used: High-Frequency Induction Welding (HFIW) for pipes ≤24", Submerged Arc Welding (SAW) for large diameters/thick walls, and Electric Resistance Welding (ERW). HFIW is most common, using electromagnetic induction to heat edges before pressure welding. SAW provides deeper penetration for heavy-wall pipes. ERW is cost-effective for mass production of small-medium sizes.
Q2: What welding parameters are critical for quality?
A2: Key parameters include: welding current (20-50kA for HFIW), frequency (100-400kHz), welding speed (10-60m/min), squeeze pressure (200-600N/mm²), and V-angle (3-6°). Optimal parameters depend on wall thickness and diameter. Automated systems continuously adjust parameters to maintain consistent weld quality despite material variations.
Q3: How is weld seam quality ensured?
A3: Multiple controls are implemented: Online eddy current testing detects surface defects, ultrasonic testing finds internal flaws, and X-ray inspection checks fusion quality. Weld seams undergo macro/micro examination, hardness testing, and corrosion testing. Process qualification welds are destructively tested before production begins.
Q4: What post-weld treatments improve performance?
A4: Common treatments include: normalizing to refine grain structure, weld seam annealing to reduce hardness, grinding for smooth surfaces, and shot blasting for stress relief. For critical applications, full-body heat treatment (normalizing or quenching/tempering) enhances mechanical properties. These treatments improve corrosion resistance and fatigue life.
Q5: How is weld integrity tested?
A5: Multiple test methods are employed: Hydrostatic testing at 1.5-2.5x working pressure, flattening test (pipe compressed to 2/3 height without cracking), reverse bend test (180° bending over mandrel), and guided bend test for weld ductility. Microscopic examination checks fusion quality and absence of inclusions. Testing frequency follows applicable standards (e.g., 5% of production lot).
