At what pressure is the use of cast iron permitted?

The use of cast iron is generally permitted at a pressure of 15 PSI or a temperature of 250 degrees Fahrenheit. This guideline is established primarily due to the material properties of cast iron, which can become brittle at higher pressures and temperatures. At 15 PSI and 250 degrees Fahrenheit, cast iron can perform adequately without risk of failure.

The limitations of cast iron arise from its structural integrity and resistance to thermal expansion. When exposed to pressures exceeding this threshold, the risk of developing cracks or catastrophic failure increases, as cast iron may not have the toughness needed to withstand greater stress or temperature fluctuations.

Other options present pressure and temperature allowances that exceed the thresholds typically recognized for cast iron, which raises the possibility of failure due to the material's inherent brittleness under those conditions. Thus, the correct answer provides a safe operating condition for cast iron that aligns with industry standards and material limitations.