The correct answer is B) avoid rapid temperature changes and follow recommended operating procedures. The key to ensuring a long service life for boiler refractory materials is to avoid subjecting them to rapid temperature changes. Sudden temperature fluctuations can cause the refractory materials to crack, spall, or degrade prematurely. Following the manufacturer's recommended operating procedures, which typically involve gradual heating and cooling, helps to maintain the integrity of the refractory over time. The other options are incorrect because: A) maintaining a high furnace temperature at all times can actually accelerate the degradation of the refractory; C) properly securing the refractory is important, but it does not address the issue of temperature changes; and D) patching refractory with plastic chrome ore is a temporary fix, not a long-term solution to ensure a long service life.