Technical bolting is essential in every piece of machinery and it requires precision to make even the smallest of the connections tight and leak-proof for optimum safety. Tensioning and torquing are the major methods of bolting that attain the best axial load. Bolt tensioning provides even tension throughout the flange and it is faster. Let’s delve into tensioning to see how effective and applicable it is in mechanical field services.
What are Tensioning Methods for Technical Bolting?
Tensioning entails axial stretching of a bolt to achieve the acceptable bolt load. It uses hydraulic pressure and multiple studs are tensioned simultaneously for a uniform load. The technician may use hydraulic nuts or bolt tensioners and he needs longer bolts with a seating area around the nut. Tensioning many bolts concurrently ensures uniformity of the applied load.
Tensioning Technical Bolting Procedure
Hydraulic tensioning takes four steps:
- Fit the bolt tensioner over the stud
- Apply hydraulic pressure on the tensioner, which in turn stretches the stud.
- The nut winds down against the joint face
- Release the pressure and remove the tool.
The tensed bolt tries to contract, exerting the required clamping force across the joint.
Types of Hydraulic Tensioners
Tensioning requires specialized tools known as hydraulic tensioners. These apply hydraulic pressure to tighten bolts exactly to your specifications. Here are two common types:
Topside Hydraulic Bolt Tensioner
This type of tensioner is a short and wide design for limited vertical clearance applications that are radially open. The single stage bolt tensioner is ideal for the petrochemical industry, especially for oil and natural gas pipelines. It is suitable for windmills, compressor covers, heat exchangers, and boiler feed pumps.
Multi Stage Hydraulic Bolt Tensioner
A multi stage hydraulic bolt tensioner has a central tie rod where two load cells act. It works with double load capacity and it is ideal for all instances where there is restricted radial width. This tensioner is suitable for installations like windmills, gas turbines, and gearboxes.
Specification for Bolt Tensioning Technical Bolting
A client who needs hydraulic tensioning services should provide the following vital details to a technical dealer:
- Is it a multi stage or topside tensioning tool?
- Bolt sizes such as M42
- The maximum tensile force required
- The strength grade of your bolt.
Is it 8.8 or 10.9? The answer here may help if you do not know the maximum tensile force.
How Tensioning Differs from Torquing for Technical Bolting
Firstly, it is important to remember the principle on which the bolt operates. A bolt has elastic properties which makes it stretch and try to restore its original length, hence producing a firm joint. Both tensioning and torquing are acceptable techniques to seal joints in technical bolting.
Torquing relies on linear tension-torque relationship to fasten bolts and it is affected by friction, lubrication types and thread tolerance. Let’s see the main differences between the two bolting methods:
- Bolt tensioning stretches a fastener while bolt torque exerts a rotational force on the fastener.
- Tensioning is ideal for large bolts, while torquing works usually for smaller fasteners.
- It eliminates inaccuracies caused by friction in torquing.
Torquing exhibits accuracy levels of +/- 30% whereas tensioning improves accuracy to plus or minus 10%.
- While torquing applies massive mechanical effort, tensioning uses simple hydraulic pressure to achieve firmer fastening.
- Tensioning is more sophisticated than torquing, hence it requires experts to apply stud tensioning perfectly. On the contrary, torquing is simple and the equipment used is readily available.
- Tensioning is more expensive than torque because the tools used are costly.
When is it Better to choose Tensioning for Technical Bolting?
Tensioning stands out when it comes to the choice of bolting method in mechanical field services because it is friction-free and torsion-free. It is ideal in several instances, determined by various factors compared to torquing.
What to Consider
- Accessibility and nature of joint: Tensioning is a viable option when the joints are critical and you cannot afford to gamble on the connection. When there is a tight clearance between studs it is advisable to do tensioning in stages. Tensioning guarantees a stronger joint for very sensitive devices that would otherwise remain apparently loose after torquing.
- Stability and ease of control: Bolted connections need stable and reliable joints. Torquing may compromise the integrity of intensive machinery. Therefore, tensioning is the way to dispel fears of weak joints.
- Extra measurements and other considerations: Unlike torquing, tensioning gives room for extra bolt diameter, washer diameter and washer thickness and saves time. It works incredibly for varying load requirements, bolt grade and free stud protrusion length.
- Minimal load sharing: Tensioning is suitable when you want to eliminate cross talk between adjacent studs. The ultimate goal is to achieve a very tight joint.
- Accuracy: It is needless to say that if accuracy is your priority, you cannot go for anything less than tensioning for technical bolting.
- Fast services: Tensioning reduces delay and rework as it prevents the galling of threaded fasteners. It simultaneously achieves gasket compression and bolt load on the entire joint.
- Skilled expertise: Undoubtedly, tensioning requires trained personnel. It is a bit complex and only an expert would deliver the desired outcome in field machining.
- Relevant equipment: Tensioning requires gadgets that are not readily available in every mechanical outlet. If they are within reach, you have no option. Nevertheless, acquiring equipment from far should not be an excuse – no substitute for quality. Work with a bigger budget for tensioning compared to torque.
- Safety consideration: Bolting can be hazardous when every step of installation is handled manually. Tensioning is a hands-free technique. Hence, it reduces the possibility of accidents when bolting.
Specialty Services from Leverage Mechanical
Leverage Mechanical Services is the hub of intelligent technical bolting services. We have all the equipment needed for successful bolting and joint integrity, including bolt tensioners, hydraulic torquing wrenches, continuous rotation tools, flange spreaders, nut splitters, and technical software for all bolting needs. Whether you need technical bolting or field machining, our experts are here for you. We serve facilities all throughout Texas, Louisiana, and the Gulf Coast. Choose our team for quick turnaround and 24/7 service. Contact us now to get a quote.