What torque pattern is used when torquing a flanged surface for preformed packing?

The diametrically opposite or star pattern is employed when torquing a flanged surface for preformed packing because it ensures even distribution of the load across the flange. This method minimizes the risk of warping the flange or damaging the packing material, which could occur if the torque is applied unevenly. By tightening the bolts in a star pattern, you gradually create a uniform seal by compressing the packing evenly. This approach aligns closely with the mechanical principles involved in gasket sealing, where maintaining a consistent compressive load is crucial for preventing leaks.

Using this pattern helps to avoid localized stress concentrations that can arise when torque is applied in a simpler, more linear fashion. Overall, the star pattern optimally balances the forces applied to the flange, leading to a more reliable and effective seal when using preformed packing.