What type of pipe should NEVER be used for hydraulic lines?

The correct choice is galvanized pipe. In hydraulic applications, the materials used for piping must be able to withstand high pressures and the corrosive effects of hydraulic fluids. Galvanized pipe, which is coated with a layer of zinc to prevent rusting, is not suitable for hydraulic lines because the zinc can react with many hydraulic fluids and may lead to significant corrosion over time. Additionally, galvanized pipes can experience issues such as flaking from the zinc coating, which can introduce contaminants into the hydraulic system and lead to blockages or damage to hydraulic components.

Additionally, cast iron and PVC pipes also pose challenges when used for hydraulic systems. Cast iron is brittle and can fail under pressure, while PVC is not rated for high-pressure systems and can be susceptible to failure when subjected to extreme conditions. Stainless steel, on the other hand, is a common choice for hydraulic lines due to its excellent corrosion resistance and ability to handle high pressures, making it a safe and reliable option.