If you’ve worked in industries like oil and gas, power generation, or heavy manufacturing, you’ve probably dealt with stud bolts—those unassuming yet critical fasteners that keep flanges, pressure vessels, and piping systems sealed tight. And if you’ve spent much time handling them, you’ve almost certainly run into galling. That stubborn, irreversible surface damage—where two metal surfaces cold-weld together during tightening, leaving rough, torn threads—doesn’t just ruin a fastener. It can derail maintenance schedules, lead to costly shutdowns, and even create safety hazards if a failed stud bolt causes a leak. As a stud bolt supplier with 12 years in the game, I’ve seen firsthand how many operators assume galling is just part of the job. Over the years, I’ve worked with hundreds of maintenance teams and plant engineers, and I can tell you: most galling is preventable. Today, I want to break down the science behind this issue, the most common mistakes that cause it, and the actionable steps we’ve learned help our customers avoid it. Stud Bolts
First, let’s get clear on what galling actually is, because understanding the root cause is the first step to preventing it. Galling is a form of adhesive wear that occurs when two metal surfaces slide against each other under high pressure, like when you’re turning a nut onto a stud bolt. Metal is made of tiny crystalline grains, and when the load is high enough (like the clamping force needed to seal a high-pressure flange), the peaks of these grains on the stud’s threads and the nut’s threads will push into each other. If there’s no lubrication or protection to separate the surfaces, the high pressure melts the tiny contact points, and the grains from one surface weld to the other. As you keep turning the nut, this weld rips, taking material from both surfaces with it. That’s why you end up with those rough, torn threads, or even a stud that snaps right off when you try to loosen it.
Galling isn’t just bad luck—it happens when three key conditions line up: high surface pressure (clamping force), relative motion (turning the nut), and two metals that are chemically compatible enough to cold-weld. Most stud bolts are made of alloy steels like A193 B7 or A193 B16, and their matching nuts are usually A194 2H or 7H. These are strong, durable materials, but they’re prone to galling because they’re similar in composition, hard, and prone to cold-welding. You’d think stronger materials would be more resistant, but that’s a common myth. In fact, harder materials often have rougher surface finishes, which increases the contact points that can weld.
Now, let’s talk about the most common mistakes I see that set the stage for galling, because once you recognize these, you can fix them before they turn into a problem. The first and biggest mistake is using the wrong lubricant or no lubricant at all. I once worked with a refinery that only used generic anti-seize compound for every stud bolt application. Generic anti-seize often has inconsistent ratios of lubricating solids like copper or graphite, or it can degrade at high temperatures (common in power plants and refineries that run at 500°F+). I asked their maintenance team to send samples; one batch they’d been using for a year had nearly half its lubricating solids missing, which meant there was no barrier between the stud and nut threads. Even worse, some teams skip lubrication entirely to save time—they think “more friction means better clamping,” but that extra friction is exactly what causes galling. The friction generates heat, which softens the metal surfaces and makes them more likely to weld.
The second mistake is surface preparation that’s rushed or incomplete. Stud bolts come from the factory with precision-machined threads, but a lot of operators don’t check those threads before installation. I’ve seen studs with tiny burrs from shipping, or even leftover mill scale that wasn’t removed. Those burrs act like tiny sharp points that concentrate pressure on small areas of the nut and stud, instead of spreading the load evenly across the entire thread. Another surface mistake: using a wire brush to clean old threads on a nut or stud during maintenance. Wire brushes leave tiny metal shavings embedded in the threads, which act like abrasive particles that scratch the surface and make galling way more likely when you tighten the new stud.
Third, there’s the mistake of mismatched materials or incorrect torque application. Wait, mismatched materials—doesn’t that mean the stud won’t be strong enough? No, I’m talking about pairing a B7 stud with a generic nut that’s not designed to match its hardness. If the nut is too soft, it will deform under clamping force, leading to uneven thread contact. If it’s too hard, it will wear the stud’s threads as you tighten. Torque application is another big one. A lot of teams use a generic torque chart off the internet, but torque is dependent on so many factors: lubricant type, thread finish, temperature, and stud material. I once had a customer who followed a chart meant for A193 B7 studs with molybdenum disulfide lubricant, but they were using a high-temperature anti-seize that changed the friction coefficient. The result? They applied 20% more torque than they needed, which created excess clamping force that led to galling on 12 studs during a flange replacement.
Now, let’s get to the good stuff—how to actually prevent stud bolt galling, step by step, based on what our team has tested and proven over the years.
First, choose the right stud bolt and nut material for your application. This isn’t one-size-fits-all. For standard low-pressure applications, A193 B7 studs and A194 2H nuts work, but for high-temperature (above 750°F) or corrosive environments, we recommend A193 B16 studs paired with A194 7H nuts. The 7H nut has a more controlled hardness that matches the B16’s higher chromium and molybdenum content, reducing the chance of cold-welding. For even more extreme cases, like nuclear power plants or chemical processing, we offer nickel alloy studs (like Inconel 718) and matching nuts, which have low friction coefficients and excellent resistance to galling even at temperatures over 1000°F. The key here is to get the hardness difference right: the nut should be 10-20 Brinell Hardness (BHN) softer than the stud. That way, if any contact occurs, it’s the nut’s threads that wear, not the stud’s—which you can replace much more easily than a stud bolt embedded in a flange.
Second, use a precision-formulated lubricant specifically designed for stud bolts and application temperature. Generic anti-seize is a no-go. I’ve worked with our in-house metallurgists to develop a line of stud-specific lubricants that test at consistent friction coefficients and hold up to extreme temperatures. For low-temperature applications (below 500°F), we recommend a copper-based lubricant with added graphite to prevent cold-welding. For high-temperature (500°F to 1200°F), a nickel-based lubricant is better because copper can oxidize and break down at higher temps. For cryogenic applications, a specialized PTFE-based lubricant that stays stable at -320°F is ideal. The rule of thumb here: never use a lubricant that’s not rated for your operating temperature. Also, apply the lubricant evenly across the entire stud and nut threads—don’t just dab a little in the center. Use a small brush or a controlled applicator to make sure every thread has a thin, uniform layer.
Third, nail the surface preparation before installation. This is the step most teams skip, but it’s the difference between a smooth installation and a galled stud. First, inspect every stud and nut before you touch it. Run your finger along the threads to feel for burrs, or use a magnifying glass for close checks. If you find a tiny burr, use a fine abrasive stone (like a 600-grit silicon carbide stone) to smooth it out—never use a wire brush, which leaves embedded shavings. For used studs during maintenance, clean the threads with a non-abrasive thread chaser (not a tap, which can alter the thread dimensions) to remove old lubricant and debris. Also, make sure the mating surfaces of the flange are flat and free of debris—if the flange isn’t sitting straight, the stud will bend under clamping force, leading to uneven thread contact and higher pressure on individual threads.
Fourth, control your torque and preload correctly. This is where so many teams go wrong. Generic torque charts don’t account for lubricant type, so they lead to over-tightening, which is a top cause of galling. Instead, calculate torque using the formula for your specific stud and lubricant, or use a calibration chart tailored to your product. For example, a B7 stud with our high-temperature nickel lubricant will have a different torque value than a B7 stud with a generic copper lubricant. Another tip: use torque-turn method instead of just torque alone. Torque measures how much force you’re applying to the nut, but torque-turn measures the angular rotation of the nut after it touches the flange, which gives a more accurate preload. This method reduces excess clamping force that causes galling, especially for large diameter studs (1 inch and above). Also, never reuse old studs or nuts that have been galled before—even if you think you can smooth the threads, the micro-welds create weak points that will lead to more galling on your next installation.
Fifth, handle and store stud bolts correctly to avoid damage before you even use them. I can’t tell you how many times I’ve seen studs delivered with bent threads or scratched surfaces because they were tossed in a bin with other fasteners. Stud bolts are precision components, so they should be stored in individual bins or on racks designed to hold them horizontally, so their threads don’t get damaged. When moving them, use a stud rack instead of dragging them across a concrete floor. Even small scratches on the thread surface will act as pressure points during tightening, increasing the risk of galling.
Let me share a real example to put this all in perspective. Last year, a mid-sized power plant in the Midwest reached out to us with a recurring problem: every time they replaced studs on their steam headers, 10-15% of the studs would gall during tightening, leading to an average of two days of downtime per month to replace damaged studs. Their team was using standard B7 studs and 2H nuts, generic copper anti-seize, and a generic torque chart. We did an on-site audit, and found three key issues: they were using an expired anti-seize that had lost 40% of its lubricating solids, they were using wire brushes to clean old threads, and they were applying 15% more torque than the chart recommended for their lubricant. We replaced their anti-seize with our high-temperature nickel lubricant, trained their maintenance team to use thread chasers instead of wire brushes, and provided a custom torque chart calibrated for their studs. After that, their galling rate dropped to less than 1%—and they saved over $20,000 a month in replacement studs and downtime. That’s the kind of result that comes from paying attention to the small details, not just buying the cheapest stud bolt on the market.
I know that for plant teams, every minute of downtime costs money, and every part of maintenance feels like a checklist item. But galling isn’t inevitable—it’s a solvable problem. The key is to stop treating stud bolts as a commodity and start treating them as critical components that need the right material, preparation, and care. As a stud bolt supplier, our job isn’t just to sell you fasteners—it’s to help you avoid the headaches that come with galling, shutdowns, and safety risks.
If you’re dealing with recurring galling, or just want to make sure your next project goes smoothly, we’re here to help. Our team of metallurgists and maintenance specialists can assess your current setup, recommend the right stud bolts and lubricants for your specific operating conditions, and even provide on-site training for your team to implement these best practices. We don’t just supply products—we partner with our customers to solve real problems, because we’ve been in your shoes, dealing with the same pressure to keep operations running.
Fully Threaded Bolts Reference
- Buckley, D. H. (1981). Surface effects in adhesion, friction, wear, and lubrication. Elsevier.
- Stud Bolt and Flange Fastener Standards Committee. (2019). Recommended Practices for Stud Bolt Installation and Galling Prevention. American Petroleum Institute.
- Dieter, G. E. (1986). Mechanical metallurgy (3rd ed.). McGraw-Hill.
- ASME Boiler and Pressure Vessel Code. (2022). Section VIII, Division 1: Rules for Construction of Pressure Vessels. American Society of Mechanical Engineers.
Handan Jihao Fastener Co., Ltd.
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