STRESS ANALYSIS OF ASME SECTION X FLANGES USING CLASSICAL LAMINATION THEORY

Fiber Reinforced Plastic composite flanges are extensively used in pressure vessels and pipping systems working under harsh and corrosive environment. ASME section X gives the design procedure to follow to verify the mechanical integrity and leak tightness of these flanges. Unfortunately, this method treats FRP bolted flange joints using the same analytical approach as that of ASME section VIII div. 1 which is derived for metallic flanges. The approach was developed in the late 30’s for flanges having isotropic material properties while the flexibility of the flange different elements and their elastic interaction is ignored. In the absence of a suitable approach such as one based on classical laminate theory, the structural integrity of FRP bolted flange joints remains an issue and some flange classes and sizes will suffer structural failure. It is proposed to study ASME section X flanges using a recently developed model based on the classical laminate theory and the flexibility of the different elements to identify those critical ones that needs particular attention with regards to composite material selection and bolting and pressure limits. Parameters such as flange ring rotation and stresses in the bolts, flange and gaskets will be investigated. The study on the strength of FRP flanges described in ASME section X RD-620.1 table, will reveal the most critical size and class flanges and their highly stressed locations. The critical stresses and their locations on the flange will be given for each flange. The study will be conducted on flanges of NPS 1 to 48 and classes from 25 to 150. The analysis will be conducted on flanges fabricated out of Fiberglass Reinforced Plastic (FRP) laminates, manufactured with vinyl ester resins and various types of fibrous glass reinforcing. The study shows that FRP flanges of class 25 and 50 are most vulnerable and should be less loaded.