Why is a Monel gasket used in HF acid piping?

• A. Because of its high resistance to acid
• B. Because it is the cheapest option
• C. Because it is non-magnetic
• D. Because it conducts heat well

Answer: (A)

Chemical compatibility with hydrofluoric acid is the key factor. HF is extremely corrosive to many metals, so the gasket material must resist chemical attack to keep a reliable seal. Monel, a nickel–copper alloy, is resistant to HF attack much better than many other metals, so it maintains integrity and prevents leaks in HF piping. Its composition helps form a protective surface that minimizes fluoride ion corrosion, which is why it’s commonly used in this service. The other reasons—cost, magnetism, or how well it conducts heat—don’t address the main issue here, which is resisting HF corrosion.