Question 1

How do I select the correct flange pressure class?

Accepted Answer

Start with the design pressure and temperature. Look up the ASME B16.5 pressure-temperature rating table for your flange material group. Select the lowest class whose rating exceeds your design conditions at the maximum operating temperature. Include a safety margin and consider upset/transient conditions. Note that most refinery specifications default to Class 150 for utility services and Class 300 for process services.

Question 2

What causes flange leaks and how are they prevented?

Accepted Answer

Common causes: insufficient bolt preload (most frequent), uneven bolt tightening, damaged gasket or flange face, thermal cycling, and vibration-induced bolt relaxation. Prevention: use calibrated torque wrenches with star-pattern tightening sequence (minimum 3 passes), inspect flange faces for scratches >Ra 3.2 μm, verify gasket type matches service conditions, and consider controlled bolt tensioning for critical joints.