Q: Why is carbon steel generally not chosen for highly corrosive services?
A: Unlike stainless steel (e.g., 316L), which contains chromium and other elements that form a passive protective layer, carbon steel lacks sufficient alloying elements for such protection. It corrodes readily in acidic, alkaline, or chloride-containing environments-3-8.
Q: At what temperature does carbon steel pipe face limitations?
A: For sustained service, carbon steel's strength decreases significantly above 450°C. Above this temperature, oxidation (scaling) also accelerates. For higher temperatures, alloy steels or stainless steels (like TP316H) are specified-6-10.
Q: What is a "branch connection" and what are common types?
A: A branch connection is where a smaller pipe (branch) is connected to a larger pipe (run or header). Common types include unreinforced fabricated tees (stub-ins), reinforced fabricated tees, and proprietary branch connection fittings (e.g., Weldolets®)-9.
Q: What is "reinforcement" for a branch connection, and when is it required?
A: Reinforcement involves adding material (via a pad or the inherent extra thickness of the pipes) around the branch opening to compensate for the metal removed. It is generally required by codes like ASME B31.3 unless specific exemptions for tees or couplings apply-9.
Q: What is "hot tapping" and what are the key considerations for wall thickness?
A: Hot tapping is welding a branch connection onto a pipe that is still in service and under pressure. A key risk is burn-through. To minimize this, a minimum remaining wall thickness (e.g., 3/16 inch or 5 mm) in the header pipe is often required to contain pressure during welding-9.
