Hydraulic bolt tensioners are more commonly used for bolting applications in Europe than in the United States. Typically, hydraulic tension is used on fasteners with a bolt diameter of 2″ or greater, but can also be used on bolts as small as ¾” in diameter.
Tensioners are common in underwater applications (both above and below water), wind turbines, and power generation applications, but are less commonly used in the oil and gas industry. However, in the oil and gas industry, tensioning tools are commonly used on fasteners in critical bolted joints such as heat exchangers and other large pressure vessels.
By covering the wrench 50% or more, you can achieve smoother, more precise joint compression than with a torque wrench.
One of the main advantages of bolt tensioners is that they eliminate the friction factor on the face of the bolt and nut. In fact, keys are generally more accurate, achieving an accuracy rate of plus or minus 10% versus 30%.
Traditionally, using hydraulic bolt tensioners means you can reuse your bolts more often because you don’t have to worry about seizing or frictional forces on the fastener. While this is true for lab applications, note that in the field you must consider operating conditions such as temperature and pressure which will affect fasteners over time.
Use of bolt tensioners in the field
Bolt tensioning is presently the favored strategy for fixing bolts and studs in every basic application. Bolt Tensioners are intended for various applications including, heat exchangers, and boiler feed pumps, compressor covers, pipe flanges and pressure vessels wind turbines, etc. When tightening bolts, the bolt tensioner uses pure tension to tighten the bolt directly without torsional shear, lateral force and no frictional damage to the stretching of the joint contact surface. This is the best way to precisely control the preload force of the screw. The Hydraulic Bolt Tensioner allows you to pre-load or dismount multiple bolts at once and stretch the bolts before tightening them without rubbing the nuts, ensuring extremely high accuracy, speed and consistency. It is one of the best bolt tensioning tools Learn More
Different Type of Bolt Tensioners
Compared to the classic tightening method, the use of a bolt tensioner has significant advantages:
- Fastening without torsion stress
- Direct charging will not damage any components.
- Operation is simple and quick.
- Very high accuracy and repeatability.
- Automation is achievable and can be utilized for basic applications.
A limitation of turnbuckles is the need for greater clearance. Although this is generally not a problem with standard pipe flanges, you may not have room for a wrench on valves and other custom flanges as you will see with heat exchangers.
Also, the maximum bolt tension that tensioners can achieve is usually around 50,000 to 60,000 psi bolt preload. If you want to clamp over 60,000 psi, you probably need a special clamp.
Also, you will need an extra length of screw to tighten. The rule is that a diameter of the bolt must protrude from the nut to allow the tie rod to grip the bolt when the load cell presses on it. Therefore, to calculate the correct size, take the normal length of the bolt you would use to tighten and add an extra diameter of that bolt.
Working of Hydraulic Tensioning
Starting from the bottom of the unit, the basic parts of a hydraulic tensioner are Learn More
Nut
It rests on the flange while the bridge rests around the nut. As you can see the bolt protrudes from the nut and you need to make sure that a diameter of this bolt protrudes from the nut.
Load Cell
This sits above the nut and contains the hydraulic piston inside. A nipple is attached to the load cell to allow oil to enter at a specified hydraulic pressure from the tensioner pump.
Puller bar
It rests on the piston, which is screwed onto the screw. The hydraulic pressure in the pump and the diameter of the load cell determine the force you apply to the bolt.
A 50% overlap or slack on all other bolts is standard. While 25% coverage is possible, we do not recommend this approach as it requires more passes, is more difficult for the installer to achieve, and reduces your accuracy. To lower. So if you have 50% coverage, you have what we call Pass A and Pass B.
Bolt Tension Example
Suppose your goal is a bolt tension of 50,000 psi. You should consult with the tensioner and engineer first to ensure you understand all of your load loss factors. But in this example, you increase your Pass A by 20% over what you would do for your Pass B. Your pass B is your final bolt load. But because we’re only loading half the bolts and trying to put this pipe together and pull the joint and everything together we need to reconsider our aim so that when we bring our B pass the load transfer is happening and should balance out. Now it’s common practice to go back to your A’s and check you still have the correct bolt load and run your B’s over your A’s.
Safety of Hydraulic Tensioning
Safety around hydraulic tension is absolutely essential. Your main concern is that you are working with high pressure hydraulic fluid flowing from the tensioner pump to the load cell and then to the other tensioners. High pressure fluid can cause serious injury so always ensure it is stored properly, kept clean and that safety precautions are taken before use. If you see a worn or damaged hose or fitting, please replace it.
Also, your assemblers don’t want to be looking at the tensioner while it’s in use because if it loosens from poor thread engagement, stripping, or anything else, it will end up in a ball. Therefore, always make sure that you are to the side of the clamps and are not looking directly at the drawbar.
