Common Causes of Bolted Joint Leakage
Human Factors remains the number one cause of flange leakage, and with accredited training the candidate will become aware of all the key issues to consider prior to assembly and tightening of a bolted connection.
Uneven Bolt Stress. An incorrect tightening/assembly procedure or difficult access to fasteners can leave some bolts loose while others are over tightened and can crush the gasket. This can cause in-service leaks, especially in high temperature services when the heavily loaded bolts relax.
Improper flange alignment, especially flange face parallelism, causes uneven gasket compression, local crushing, and can cause subsequent leakage. Improper flange centerline alignment can also cause uneven gasket compression and flange leaks.
Improper Gasket Centering. If a gasket is installed off center compared to the flange faces, the gasket will be unevenly compressed and make the joint prone to leakage. Spiral wound and double jacketed gaskets usually have a centering ring that extends to the inner edge of the bolts. A sheet gasket can be cut so that its outside diameter matches the inner edge of the bolts.
Dirty or Damaged Flange Faces. Dirt, scale, scratches, protrusions, weld spatter on gasket seating surfaces, and warped seating surfaces provide leakage paths or can cause uneven gasket compression that can result in flange leakage.
Excessive Piping System Loads at Flange Locations. Excessive forces and bending moments can loosen the bolting or distort the flanges and lead to leaks. Common causes are inadequate piping flexibility, using cold spring to align flanges, and improper location of supports or restraints.
Thermal Shock. Rapid temperature fluctuations can cause flanges to deform temporarily. This is typically a greater potential problem in high temperature applications. Process variations cannot always be avoided. A related problem is temperature variation around the flange circumference (e.g., cooling on top due to rain, or cool liquid at the bottom and hot gas at the top). Where this is a problem, sheet metal shields can be installed to protect against rain or snow impingement that could cause thermal gradients across the flange and cause leakage. Such shields also serve to keep the flanges and bolts at a more uniform temperature.
Incorrect GASKET Specification and Size, this can result in blow out and flange leakage during start up or commissioning.
Improper Flange Facing. Deeper serrations than specified will prevent the seating of double jacketed or spiral wound gaskets and provide a leakage path.
High Vibration Levels. Excessive vibration can loosen flange bolts and ultimately cause flange leakage.
Non validated torque or tension values – challenge the source of all information supplied.