Determination of load capacity of a non-gasketed flange joint under combined internal pressure, axial and bending loading for safe strength and sealing

Abstract

Performance of a bolted flange joint is characterized mainly due to its 'strength' and 'sealing capability'. A number of analytical and experimental studies have been conducted to study these characteristics only under internal pressure loading. A very limited work is found in literature under combined internal pressure and bending loading. Due to the ignorance of external loads i.e. bending and axial in addition to the internal pressure loading, an optimized performance of the bolted flange joint can not be achieved. The present design codes do not address the effects of combined loading on the structural integrity and sealing ability. To investigate joint strength and sealing capability under combined loading, an extensive comparative experimental and numerical study of a non-gasketed flange joint with two different taper angles on the flange surface and with different load combinations is carried out and overall joint performance and behavior is discussed.Actual joint load capacity is determined under both the design and proof test pressures with maximum additional external loading (axial and bending) that can be applied for safe joint performance. NOTATIONS Poisson's ratio E Young's modulus of elasticity (MPa) DP Design pressure (15.3 MPa) PT Proof test pressure (23 MPa) FID Flange inside diameter (mm) FOD Flange outside diameter (mm) PT Pipe top PB Pipe bottom PS Pipe side For more clarity above mentioned notations are used. Notations used by the design code ASME Appendix-Y for hoop and longitudinal stresses are (S T and S H ) and for flange outside and inside diameters notations are (A and B). INTRODUCTIONDifferent types of flange joints evolved over the centuries and were perfectly adequate for their performance at low pressure and temperature. However, high pressure, temperature and differnt external loading applications led to sealing problems. Leakage (small and large) in flange joints, is a continued significant safety concern in terms of human life, environmental effect and cost.With the rapid advancement in technology for high pressure, high temperature and external loading applications, trends are changing. A flange joint must have adequate mechanical strength and good leak tightness, therefore it is important to evaluate the integrity and sealing performance at actual operating conditions. Available design rules [1,2] for flange joints are mainly concerned with the strength of the flanges and do not sufficiently consider sealing performance. In addition, these do not address the effect of any external loading on the integrity and sealing performance.Non-gasketed flange joints are considered as an alternative due to the 'static mode of load' under 3 bolt up and different internal pressure [3][4][5][6][7][8] and temperature loading [9-10], providing better joint strength and sealing capabilities. External loading on bolted flange joints have been discussed in [11][12][13][14][15][16][17] but these studies are only for the gasketed flange joints. Similarly other studies [18][19][20] has been done but...

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