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The 5 step guide to torque tightening for leak-free flange connections


Obtaining a leak-free flange connection can be a difficult task on-site without a plethora of equipment to fall back on. A proper gasket installation, bolts with correct tension, and an evenly divided bolt strength must be adhered to to create a good flange connection.

However with torque tightening the correct tensions can be realised for the ultimate connection for your flange.

Correct tightening of a bolt means making the best use of the bolt's elastic properties. To work well, a bolt must behave just like a spring and create equal and opposite compression force applied on the assembled components, also known as the 'tightening load'.

With tips from Wermac, here's our 5 step guide to create the ultimate torque tightening for your flange:

Use a torque wrench and suitable technique

A torque wrench is a hand-guided screwing tool, and is used to accurately set the force of the bolt. It allows the operator to measure the rotational force applied to the bolt so it can be matched to the specifications.

Techniques require quality tools and experienced colleagues who can carry out the work. Some of the most common techniques to flange bolt tightening include manual, impact, hammer, hydraulic torque, manual beam and gear-assisted torque wrench and hydraulic bolt tensioner.

Torque loss on bolted joints

An inevitability of any bolted joints is the loss of torque over time. Within 24 hours, 10% of the torque is lost in the bolt after the joint has relaxed. The more torque that is lost over time, the bigger the chance the flange will leak.

The key to reducing these effects in the installation process is by slowly bringing the flanges together in a parallel line, taking a minimum of four bolt tightening passes, and by following the corrent bolt tightening sequence. This not only creates a better connection, it also reduces ongoing maintenance costs and increases safety.

It is important to note that gasket thickness is vital. The thicker the material, the higher the gasket creep will be - resulting in torque loss.

Reduce friction with lubrication

Lubrication not only reduces the friction during tightening, it can also decreases the chance of bolt failure during installation and increases bolt life too.

Remember, variation in friction affects the amount of preload achieved at a specific torque. Higher friction results in less conversion of torque to preload. The value for the friction coefficient provided by the lubricant manufacturer must be known to accurately establish the required torque value.

Anti-seizure compounds should also be applied to both the nut bearing surface and the male threads for an easier process.

The sequence of tightening

Lightly tighten 1st boltThis is one of the most important factors of the process. Using Wermac's tightening sequence drawing, follow the below steps:

  • Move 180 degrees and tighten 2nd bolt
  • Move another 90 degrees around the flange for the 3rd bolt
  • Move another 180 degrees for 4th bolt
  • Continue bolt tightening  until all are completed
Torque Sequence

Preparing for bolt-up

The most common cause of a leaky flange is improper installation, therefore before beginning any bolting process, preliminary steps must be taken to avoid future issues.

  • Clean the flange faces and check for damage
  • Inspect all bolts for damage
  • Remove burrs from all threads
  • Lubricate threads of the bolt and surface of the nut face
  • Install and centre the new gasket
  • Check flange alignment ASME B31.3
  • Adjust position of the nuts to insure that 2-3 threads are visible above the top of the nut.

Following these 5 steps will hopefully help you in your attempts to fix your leaking flanges. As with any process of this magnitude, checks and preparations always must be done.


Photo Credit: Wikipedia


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