Plate springs - flanged connections

It is estimated that 50 to 80% of flange joint leaks are caused by insufficient bolt preload. When properly installed, all bolts are pre-tensioned by a certain amount of elongation due to tightening. Flanges heat up faster than bolts when running at operating temperature. This leads to a further increase in tension in the bolts and increased pressure on the seals. If the seals are made of soft materials (graphite, PTFE, Mica, fiber-rubber plates), additional seal deformation will occur due to thermal expansion. In these cases, once the temperature equalizes, it is unable to cover the additional seal deformation and leakage occurs due to the drop in specific pressure on the seal.

For example, for a correctly tightened flange connection DN 150, PN40, the bolt extension is approx. 0.1 mm. If the temperature difference between the flanges and bolts is greater than 100 °C, the seal permanently deforms by 0.1 mm - complete loss of preload in the bolts.

Pallet springs are an effective solution to the problems described above because they are capable of significantly increasing the elasticity of the bolted joint. By using two springs in the previous example, instead of 100% loss of bolt preload, we would only lose 9%!

Agreeing and disagreeing arrangements of disc springs

!Consistent and discordant arrangements](/files/Articles/Talirove_springs_prirubove_joints/live-loading-usporadani.png)

Flanges suitable for the use of plate springs:

• Critical flange joints where media leakage can cause a crash
• Flanged joints with large temperature changes
• Relaxation of bolts or flange joint seals under operating conditions is expected
• Repeated leakage problems
• Loosening of bolts by vibration

Experience from refineries and petrochemical plants confirms that the use of disc springs on critical flange connections has proven to increase their tightness.

Reasons for loss of preload in bolts:

• Seal deformation and relaxation under load
• Plastic deformation and relaxation of bolts
• Vibration
• External forces on the flange connection
• Differential thermal expansion of flanges and bolts

Properly designed disc springs are capable of increasing the elasticity of a bolted joint by 7-15 times!!! It is the most effective method of increasing the tightness of critical flange joints and reducing emissions from equipment.

Pokorny designs and supplies disc spring kits for critical flange connections.