A325 bolts are the core component of thousands of steel structures in Argentina. But many fail prematurely—and almost always for the same reason: the wrong coating.
What are A325 bolts and where are they used?
A325 bolts are high-strength fasteners defined by ASTM A325, designed to join steel elements such as beams, columns, and frames. They are used in mining, industrial construction, oil and gas, electric power, solar energy, transportation, and infrastructure—any application where joint integrity is critical and cannot tolerate failure.
The problem: corrosion in A325 bolts
A well-designed structure can fail if its fasteners are not properly protected. Corrosion in A325 bolts leads to loss of preload, thread seizing, and, in aggressive environments, delayed failures that compromise structural integrity. The associated costs are not just those of the component: they include plant shutdown, rework and, in the worst case, replacement of the entire structure.
Why Hot-Dip Galvanizing Fails in A325 Bolts
Hot-dip galvanizing is historically the most common solution—and also the one that causes the most problems specifically with A325 bolts.
A325 bolts are high-strength fasteners. This means that any modification after heat treatment that alters their mechanical properties will cause them to fall out of specification. Hot-dip galvanizing deposits a thick layer of zinc, which alters thread tolerances and necessitates additional machining to accommodate the nut. This thread re-tapping is not a minor detail: there is a real risk of reducing the component's strength and rendering it non-compliant.
In addition, the immersion process can generate internal stresses in the steel, increasing its susceptibility to embrittlement in service—a critical problem for A325 bolts operating under sustained loads.
The result: an A325 bolt that comes out of the process with a correct appearance but with compromised properties.
What a good coating for A325 bolts should have
To properly protect an A325 bolt without compromising its mechanical integrity, the coating must meet three non-negotiable conditions:
1. Controlled thickness: The coating cannot alter the thread tolerances. This rules out processes that deposit thick and irregular layers. A precision coating for A325 bolts maintains the component's original dimensions and allows assembly without subsequent machining.
2. Non-electrolytic process: Electrolytic processes can introduce hydrogen into the steel during application, generating internal microcracks that compromise the component's strength. In an A325 bolt operating under sustained load, this is an unacceptable risk.
3. High Corrosion Resistance: The coating must guarantee long-lasting protection under real-world operating conditions—weather, humidity, salinity, thermal cycling—without premature degradation.
Laurentcoat®, the laminar zinc coating developed and applied by Chousa, meets all three conditions. As a non-electrolytic process with thermal curing, it eliminates the risk of hydrogen embrittlement, maintains the original thread tolerances on A325 bolts, and offers high corrosion resistance without the need for subsequent machining.
Do you have A325 bolts in your project?
Hot-dip galvanizing is a real, known, and preventable risk. The good news is that the problem has a solution: coatings with precise thickness control, such as Laurentcoat®, protect A325 bolts without altering thread tolerances, compromising their mechanical properties, or requiring subsequent machining.
Are you specifying a coating for A325 bolts or want to check if the current treatment is correct?
You can contact us at info@chousa.com.ar and get in touch with our technical team.