Design bolt loading in a bolted flange connection is difficult to obtain because of elastic interaction. Elastic interaction data is presented for two different pipe flanges@ three different gasket styles and two different bolting patterns. An algorithm that compensates for elastic interaction is given. Uniform bolt preload (??2%) is obtained in a single pass bolt-up operation. The algorithm is based on experimentally obtained interaction coefficients. Important results are: ? Elastic interaction can cause individual bolts in flanges with spiral wound gaskets to lose up to 98% of their initial preload when adjacent bolts are tightened. ? The average bolt stress can be 25-50% below design with a spiral would gasket even with a multi-pass (3 pass) bolting procedure. Publication of this document - WRC Bulletin No. 408 was sponsored by the Committee on Bolted Flanged Connection of the Pressure Vessel Research Council