Q1: What is the workhorse nickel alloy for high-temperature, corrosive refinery service?
A1: ASTM B444/B829 Alloy 625 (UNS N06625). It is used for welded pipe in severe environments like flue gas desulfurization (FGD) systems due to its outstanding corrosion and oxidation resistance.
Q2: Which titanium grade is most common for welded pipe in aggressive chloride service?
A2: ASTM B862 Grade 2 (Commercially Pure Ti). It offers an excellent balance of corrosion resistance (especially to chlorides and oxidizing media), formability, and weldability.
Q3: What does the "L" suffix mean in grades like 304L or 316L?
A3: "L" stands for "Low Carbon" (typically ≤0.03%). This is crucial for welded fabrication as it minimizes the formation of chromium carbides in the heat-affected zone (HAZ), preventing "weld decay" (intergranular corrosion).
Q4: What is "Hydrostatic Test Pressure" and how is it determined for API 5L pipe?
A4: It's a mandatory pressure test using water. For API 5L, the minimum test pressure is calculated based on the grade's specified minimum yield strength (SMYS), wall thickness, and diameter, typically reaching 90-95% of SMYS.
Q5: What is the primary welding method for large-diameter, thick-wall line pipe?
A5: Submerged Arc Welding (SAW), either double-seam (DSAW) for diameters >24" or spiral (HSAW). It provides deep penetration, high deposition rates, and excellent quality for longitudinal seams.
