Q1: What are the standard connection methods for Q235B pipes?
A1: Five primary methods are used: welding (most common), threaded connections (for small diameters), flanged joints (for frequent disassembly), grooved couplings (for quick installation), and mechanical compression fittings. Selection depends on pressure requirements, accessibility, and whether disassembly is needed. Welded joints provide the strongest, most leak-proof connections for permanent installations.
Q2: What welding techniques are recommended for field joints?
A2: Shielded metal arc welding (SMAW) using E6013 or E7018 electrodes is most versatile for field work. Gas metal arc welding (GMAW) offers higher productivity for larger projects. For critical joints, tungsten inert gas (GTAW) root passes ensure quality. Preheating to 50-100°C is recommended for wall thicknesses >12mm or ambient temperatures <5°C to prevent cracking.
Q3: How should threaded connections be prepared?
A3: Pipe ends must be properly chamfered (30-45° angle) before threading. Threads should be cut to ANSI B1.20.1 specifications using sharp dies. After threading, remove all metal chips and apply thread compound or PTFE tape. Use proper thread engagement (typically 5-6 full threads for NPT). Avoid over-tightening which can distort threads and cause leaks.
Q4: What are the pressure ratings for different connection types?
A4: Welded joints can match the pipe's full pressure rating. Threaded connections are limited to ~300 psi for small diameters. Flanged connections vary by class (e.g., Class 150 = 285 psi at 100°F). Grooved couplings typically handle 75% of welded joint ratings. Always consult manufacturer specifications as ratings decrease with temperature increases.
Q5: How are dissimilar material connections handled?
A5: Special techniques include: using bi-metallic transition fittings, isolation flanges with dielectric gaskets, or special filler metals when welding. For galvanic couples (e.g., Q235B to copper), dielectric unions or protective coatings prevent corrosion. Thermal expansion differences must be accommodated in the design through expansion loops or flexible connectors.
