What are penetrating fluids and how do they work?

Metal fasteners such as nuts, bolts, rivets and screws are manufactured with exposed surfaces that are protected against corrosion caused by oxidation. However, when they are fitted and tightened, friction can remove the protective film, putting the parts at risk of rust and allowing microscopic debris and dust to cause them to seize.

Components that won’t budge require an effective solution to free them. While many operators and engineers resort to brute force, blowtorches and long-handled tools for leverage, these extreme measures can cause irreversible damage to parts. Fortunately, there is an easier solution: applying penetrating fluid.

Manufactured by respected brands such as Morris Lubricants, penetrating fluids are an effective solution, but they do have limitations. Here, we look at these useful oils, how they work and the applications for which they are suited.

What are penetrating fluids?

Specifically formulated to loosen corroded, frozen or rusted mechanical parts such as bolts, nuts, chain links and rivets, penetrating fluids are low-viscosity liquid blends of light lubricating oils and solvents. Because of this formulation, they are sometimes referred to as “penetrating oils”.

How do penetrating fluids work?

The formulation of penetrating oils gives them the properties required to release stubborn components that have seized.

They are designed to have a low viscosity. Composed of light oil, they have an extremely thin consistency compared with grease or even conventional engine oil. This allows penetrating fluids to flow easily and reach deep into the areas where they are most needed, including places where rust has taken hold.

Penetrating oils are also engineered to have low surface tension. This means that they can draw themselves through microscopic threads and gaps. Defying gravity and without the need for external pressure, they penetrate deeply into rusted joints to help release them.

The thin oil used in penetrating fluids is combined with a solvent. As liquids capable of dissolving other substances, the solvents in these fluids can chemically break down iron oxide, dried grease, mineral scale, dirt and other troublesome deposits that have fused metal components together.

After the rust and other debris have broken down, penetrating fluids also provide short-term lubrication, reducing friction and allowing nuts and bolts to be turned more smoothly and easily.

In simple terms, the oil is designed to flow into and penetrate parts, carrying the solvent to where it is required to dissolve the material that is causing a part to seize. It leaves behind an oily residue that makes movement possible.

Common uses for penetrating oils

Today, penetrating oils are frequently used in both households and industrial environments. They are best known for freeing rusted or stuck parts such as screws, nuts, bolts, chain links, rivets and pipes. However, they are also used to displace unwanted moisture from metal surfaces and electrical contact points.

The solvents they contain mean that they are often used to dissolve difficult-to-remove residues such as tar, adhesive or gum. Their ability to provide temporary lubrication also means that they can be used to remove grime that has collected on handheld tools.

Can a penetrating fluid be used as a lubricant?

It is worth noting that penetrating oils are designed to be a short-term solution. Many users see how effectively they lubricate and remove rust from bolts and believe that they can be used interchangeably with a corrosion inhibitor or dedicated lubricant. While penetrants share some of these properties, they are a stopgap rather than a permanent solution.

In penetrating oil formulations, the solvents are often volatile, leaving behind a thin lubricating film. This remaining light oil will wear away far faster than a dedicated lubricant, such as grease or oil, leaving metal components exposed to metal-on-metal friction and wear. Similarly, penetrants cannot serve as corrosion inhibitors over an extended period; otherwise, parts will be at greater risk of rust and other corrosive forces.

For best results, use penetrating oils only for the temporary tasks they are designed to perform.

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