Unlike other industries like mining, heavy machinery, oil and gas, etc. where bolting services are crucial for every maintenance shutdowns, the infrastructure industry usually requires accurate controlled bolting services only one-time. However, it is important to get it right the first time as it can lead to a weak structure. In this article, we will highlight the factors to be considered while bolting, choosing the right torque wrench and how to achieve load accuracy.
To achieve joint integrity, various factors are taken in to consideration. One of the critical factor involved is the bolt load accuracy. These factors are taken in to consideration to control the vibrations and temperature on the bolt load. To understand this, we need to first understand the science behind controlled bolting.
As mentioned earlier, infrastructure bolts are rarely re-opened once bolted. Since, this is a one-time job, the fasteners are tightened to a higher degree than other fasteners. In the infrastructure industry, bolts used are of grade class 8.8, 10.9, etc. In some cases, High Strength Friction Grip (HSFG) bolts are also used. For high strength structural bolting, the fasteners used in assembly are as per EN 14399 standards. These fasteners consist of a bolt, nut, and two washers. All the bolts are preloaded more than the acting load on the bolts after the completion of bolting services.
Another important factor in achieving bolt load calculations through torque tools is lubrication. These bolts are pre-lubricated with coatings that can withstand the environment temperature and weather conditions to avoid corrosion. When applying torque on a bolt, the load generated in the bolt will be mentioned by the manufacturer. It is mentioned keeping the deterioration of the lubrication during storage and the time frame between manufacturing to installing the bolts.
The bolt load accuracy is impacted due to long duration between procuring, storing and installation of the bolts. Improper storage can further deteriorate the fastener’s physical and mechanical properties, which causes a significant difference between the current load calculation and actual load requirement.
As discussed in our previous article on why do torque wrenches breakdown, side load is a crucial factor that affects the accuracy of the bolt load and life of the tool. Improper reaction arm positioning causes side load, therefore it is important to use the right reaction arm and position it properly.
Pre-inspecting the bolts is very important to measure the difference between current and actual load requirement. Infrastructure bolts are tightened initially with mechanical torque wrenches which come with the feature of pre-setting the torque value and achieving bolt load accuracy in a calculated manner. Unlike manual torque wrenches, mechanical torque wrenches can be powered hydraulically, pneumatically, electrically or through battery. However, while selecting the right torque wrench, factors such as torque required, joint location, convenience, and many more are taken into consideration.
One such tool that fits the criteria for infrastructure companies are battery torque wrenches. Considered to be the next-generation bolting solution, they operate cordlessly without the additional requirement of a pump, FRL, or an electric socket. Apart from offering the convenience of portability, they also deliver a high power to weight ratio with an accuracy of +/-5%.
Similar to the battery torque wrenches are the hydraulic torque wrenches that offer the best power to weight ratio, they might not be as portable as battery torque wrenches but do offer the highest accuracy in a torque wrench of +/-3%.
To summarise, achieving accurate bolting in infrastructural industry is important to achieve accurate bolt load. This is only possible if the selection of the right tool, hardware, and operator skill with training is achieved. Visit us next time for more knowledge sharing articles.