Proper lubrication of your bolted flange connection is more important than you may realize. In fact, it is critical to the prevention of sealing issues, flange misalignment, bolt loosening, and bolt failure. By correctly applying lubrication prior to assembling a flange, you can achieve better performance and avoid downtime.
Proper bolt lubrication makes everything from bolt-up to disassembly of the flange easier and more consistent. Using lubrication correctly, you can reduce the amount of torque required to sufficiently tighten the bolts. Eventually, when you need to disassemble the flange, using a lubricant can ease the process of removing components without damage.
Another key concern during flange assembly is maintaining a consistent clamp load. Applying generous lubrication in the threads, on the nut face, and under the head of the bolt helps to ensure the desired coefficient of friction, which in turn delivers a more consistent clamp load value. In fact, using sufficient lubrication is one of the fastest, most cost-effective, and reliable ways to achieve your desired clamp load.
Lubrication is a key factor in preventing galling, which happens when two surfaces in contact seize up as a result of two metals fusing together with little or no heat, almost like welding the two pieces together. Galling inhibits the fastener’s movement, making it a major problem for either assembly or disassembly in the field.
How does using lubrication during the assembly process help to prevent galling? Effective anti-seize compounds typically contain solids that protect the threads from galling. A good anti-galling lubrication reduces the likelihood of galling damage and helps deliver better flange sealing performance.
Inadequate or “partial” lubrication is the most common mistake that happens during the application process. If valleys of the bolt threads are only partially covered, the dry areas of the fastener will lead to uneven friction, increased Nut Factor, less clamping force than desired, and possibly variation in the bolt loads of individual fasteners. Even if you know your specific Nut Factor and use a calibrated torque wrench, inconsistent lubrication still leads to inconsistent bolt load, or clamping force.
It’s important to know the signs of proper lubrication. You should cover all working surfaces — all the threads and valleys — that will experience friction when you apply torque. Once the nut is lubricated, threaded on, and tightened, you should see the lubricant flowing into a large bead under the nut face. This is a sign that all necessary surfaces have been adequately lubricated.
When it comes to flange assembly, lubrication should never be an afterthought — instead, consider it as part of your upfront planning. When applied properly, the right lubricant will ease assembly and prevent issues caused by galling.