It is widely known that resonance can quickly lead to failure in vibrating bolted flanged pipe joints. Condition monitoring is performed time to time in some industries for smooth operation of a system, whereas mostly trial-and-error tests are performed to control vibration. During all this process, the inherent design problems are not considered. A bolted flange joint in piping system is not a simple problem, being the combination of flange, gasket, bolts, and washers. The success of a bolted flanged pipe joint is defined by the “static mode of load” in the joint. However, it has been recognized that a “dynamic mode of load” governs in a gasketed bolted flanged pipe joint, which leads to its failure due to flange rotation, providing flange yielding, fatigue of bolts, and gasket crushing. This paper presents results of detailed 3D finite element and mathematical modal analysis under bolt up to determine natural frequencies and mode shapes of gasketed flanged joints with and without raised face in comparison to the nongasketed flange joint. 1. Introduction Since the advent of bolted flanged pipe joints and their applications in industries, leakage is the major causes of their failure. The problem becomes worst under dynamic loading applications such as in mill digester pipes during transfer of pulp. Traditional gasketed flanged joints are claimed to be problematic even during bolt up due to “dynamic mode of load” [1–6]. This is concluded due to the flange rotation, flexibility of gasket hence bolt loosening and leakage [1, 2, 4]. For large diameter flanges, with bolts diameter more than 18？mm, use of hammering for bolt tightening provides worst effect resulting in gasket crushing and flange yielding [1, 2, 4]. This not only increases maintenance, but also damages the joint permanently. This shows that inherent flange design problem is not considered. To avoid and control flange rotation, raised face of the flange in many industrial applications is machined [1, 2]. Keeping in view the above mentioned problems, associated with the conventional gasketed joints used in industry, several alternatives to these require consideration. For this, a nongasketed joint, concluded as an alternative for its “static mode of load,” during experimental and analytical studies by [1–4], is analyzed using detailed comparative 3D finite element modal analysis in comparison to the conventional gasketed joints with and without raised face to observe behaviour of both the joints in detail under applied bolt-up conditions. Natural frequencies and mode shapes for both the joints
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