Q1: Which is the primary grade for welded boiler tubes and superheaters?
A1: ASTM A178 Grade A (C-minimum carbon steel) or Grade C (C-Mn steel) for ERW tubes. They offer good strength and weldability for moderately high temperatures.
Q2: What alloy grade is used for high-temperature service above 1000°F (540°C) in power plants?
A2: ASTM A213 T11 (1.25Cr-0.5Mo) or T22 (2.25Cr-1Mo). These chromium-molybdenum alloy steels offer improved creep strength and oxidation resistance compared to carbon steel.
Q3: What is the key concern when welding ASTM A106 Grade B pipe for high-temperature steam service?
A3: Controlling the welding heat input to preserve the fine-grained microstructure of the normalized base metal, ensuring good creep resistance in the weld zone.
Q4: Why is ASTM A672 pipe often used for large-diameter, high-pressure process vessels?
A4: ASTM A672 covers electric-fusion-welded pipe for high-pressure service at moderate temperatures. Specific grades like B70 (normalized) allow for large fabricated sizes not feasible with seamless pipe.
Q5: Which stainless grade is common for pressure vessels handling corrosive process streams?
A5: ASTM A312/A358 TP316/316L. The addition of molybdenum provides superior resistance to pitting and crevice corrosion from chlorides compared to TP304/304L.
