Which of the following is an alloy commonly used for piping due to corrosion resistance?

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Corrosion resistance in piping comes from using materials that form a protective surface and stay strong in harsh environments. Stainless steel is an alloy of iron with chromium and other elements. The chromium creates a thin, self-healing layer of chromium oxide on the surface, which acts as a barrier against water, air, and chemicals. This passive film prevents rust and reduces corrosion, allowing the pipe to last longer in environments that would corrode plain steel. Adding nickel helps keep the metal tough and ductile, while molybdenum further boosts resistance to chlorides and aggressive chemicals. Because of these properties, stainless steel pipes are widely used for water, chemical, oil, and high-temperature services.

Cast iron, lacking that protective alloying, tends to corrode and rust and is more brittle, so it isn’t favored for corrosion-resistant piping in many applications. Plastic isn’t an alloy at all—it's a polymer—so while it can resist some forms of corrosion, it isn’t the metallic alloy typically chosen for piping that must handle high pressures and temperatures. Ceramics are hard and heat resistant but are brittle and not suitable for general piping needs where flexibility and toughness are important.