Drilling riser flanges and assemblies with contoured bearing surfaces to reduce shear in connectors

A riser flange assembly comprising:

• first and second flanges each defining a plurality of counterbored bolt holes and having a plurality of concave bearing surfaces each disposed around one of the counterbored bolt holes;
• a plurality of bolts each having a head and a male threaded portion;
• a plurality of washers each having a convex bearing surface configured to correspond to the concave bearing surface of one of the counterbored bolt holes when one of the bolts extends through the washer and the counterbored bolt hole;
• and
• a plurality of nuts each having a convex bearing surface and a female threaded portion configured to receive the male threaded portion of one of the bolts, the convex bearing surface configured to correspond to the concave bearing surface of one of the counterbored bolt holes when one of the bolts extends through the counterbored bolt hole and is received in the nut;
• where at least one of the first and second flanges defines a plurality of recesses each bordering one of the counterbored bolt holes;
• and
• where each of the nuts defines a recess configured to align with the recess bordering the counterbored bolt hole within which the nut is disposed to removably receive a dowel that substantially restrains the nut from rotating relative to the flange during tightening of the bolts.