Avoiding leaky flanges is paramount to safety at any industrial plant. Traditional ANSI flanges have been used for decades, and are still the most common choice for plant components at petrochemical plants. However, they are prone to leakage – something which needs to be addressed.

A number of improvements have been made to pipe fittings in recent years. For example, the new pressure connections, such as those we supply at Chemipetro, practically guarantee a leak-free performance. However, flange designs, for all their variety, have remained resolutely traditional. Their tendency to leak has been improved by modern technology, but not eliminated.

Conventional ANSI flanges are fitted by bolting two faces together, compressing a gasket and creating a seal. Integrity of the joint, and loading on the bolt, largely depends on the torque applied to the bolt when it is tightened.

The torques applied to pipe flanges are very specific. Therefore the proper procedures must be followed in order to avoid under or over-tightening and gasket leakage. However, even if the flanges are tightened exactly to industrial specifications, factors such as thermal expansion, internal pressures and fluctuating loads can cause movement between the flange faces.

The design of ANSI flanges means 50% of the bolt load is needed to compress the gasket, leaving only 50% to hold the pressure. Sudden, unexpected surges in line pressure, especially, can force the flange faces apart, placing stress on the bolts and creating an inefficient seal. Essentially, then, pipe flanges are inefficient.

Recent developments include patented compact flanges and API flanges. The latter withstand much higher pressures than traditional ANSI fittings.