Abstract: An improved method for cracking a hydrocarbon feedstock comprising passing the feedstock through furnace tubes at high temperatures. The improvement comprises tubes comprised of a nickel-cobalt alloy containing: nickel; 27.0-33.0 weight percent cobalt; 26.0-30.0 weight percent chromium; 2.4-3.0 weight percent silicon; 0.20-0.80 weight percent titanium; not more than 3.5 weight percent iron; not more than 1.5 weight percent manganese; not more than 1.0 weight percent columbium; not more than 1.0 weight percent molybdenum; not more than 1.0 weight percent tungsten; not more than 0.15 weight percent carbon; not more than 0.030 weight percent phosphorus; and not more than 0.015 weight percent sulfur. The improvement results in lower coking rates inside the furnace tubes, thus enhancing furnace efficiency and tube life.