Surface sensitivity study of non-gasketed flange joint

Abstract

From analytical contact pressure studies of gasketed and non-gasketed flanged pipe joints, it is known that good contact maintained over consistently large areas occurs in a no-gasketed flange joint compared with a gasketed joint, where contact is only on the seal ring portion of the gasket. However, the presence of contact pressure and a good flange surface finish does not in itself eliminate the problem of leakage. Rather, it is the surface flatness in combination with contact pressure and surface finish that is necessary to generate effective contact at the inside diameter of the flange. This occurs providing there are no gaps due to deformation arising from the welding process to the mating pipe as flow is proportional to gap height. However, the question remains as how to ensure adequate surface flatness as non-gasketed flange surfaces are sensitive to damage, which may be present in the form of surface deformation, scratches and dents or bulges. A detailed experimental study is therefore carried out to measure the surface finish and surface flatness post manufacture and welding of such flanges. Results of actual flanges were compared with solid circular plates of the same dimension with inserted shims to provide gaps in order that flow rate/gap height ratio be studied. Manufacturing issues with respect to monitoring and controlling deformations are discussed and recommendations are suggested for flange redesign, appropriate welding approaches and manual handling of non-gasketed flanges.