ASME STP-PT-036:2010 pdf free download

ASME STP-PT-036:2010 pdf free download.BOLTED FLANGED CONNECTIONS IN ELEVATED TEMPERATURE SERVICE.
One of the interesting points to come from this analysis was that there was little advantage to tightening the joint to a value esceeding twice the final stress at “tiilure.’ Similarly to Baumann. failure of the joint was defined as leakage. rather than mechanical rupture. However, this relationship is somewhat misleading due to the limitations regarding the assumptions of similarity of the bolt and flange creep and also, as detailed by Bailey. the fact that the actual value is significantly higher thati two, as there is a reduction in bolt and flange stress con’esponding to the reduction in material Young’s modulus and yield strength with increasing temperature. Therefore, the initial stresses at the start of creep are significantly lower than the initial assembly stress and it is the stress at the start of creep to which the factor must be applied. It was also stated in the paper that the sum of the individual component elastic and creep strains at any given time would be equal to the initial elastic strain imparted by the assembly load Bailey suggested in the paper that a suitable life for a joint might be 100.000 his without maintenance and 10.000 hrs with maintenance (re.Iightening.
Bailey continued his work in the field of high temperature bolted joint behavior as chairman of the Institute of Mechanical Engineers Pipe Flanges Research Committee that studied flange creep from 1936 to 1954. The focus of the study was to provide additional flange ratings to the British Standard BS 10 for standard piping flanges in order to accommodate the increasing pressures and temperatures associated with steam power generation. The first repon presented by the committee (5J detailed tests on a standard BSIO: TaNe T. g inch flange at 9OWF to l000F and 1450 psig steam pressure. The flanges were assembled, heated, steam applied internally and held steady at the operating conditions until noticeable leakage from the joint occurred. The gaskets, when used in these tests, were either metal or a vesy thin asbestos fiber (1/64 inch thick) and therefore the influence of the gasket on the joint behavior was neglected. The paper includes a diagram illustrating the concept of bolt stress relasation tFigure 3) where the elastic relasation of the bolt strain during the test (A-C’) is shown relative to the creep strain of the bolt and other joint components. Measurements of the bolt lengths and flange detlections both before and after the tests were used to determine the proportions of the creep strain and elastic strain reduction ovcumng for the joint being tested. The tests indicated that “Nut Distortion” accounted in general for less than 10% of the overall bolt creep occuriing. Nut Distortion was the term used to describe the embedment and localized creep occurring in the nut to flange and nut to bolt thread regions. This value was determined as the residual deformation when the remaining elastic and creep strain at the end of the test was subtracted from the initial assembly strain of the bolt. The paper also recommends a preliminary soak at temperature and re-tightenini of the bolts after the soak as a way of increasing the life of the joint due to the fact that the majority of the relaxation occurs in the first portion of the joint life.
Bailey continued his work on high temperature flange behavior by establishing elastic stress and deflection relationships for the joint components based on ring theory in Part I nt Bailey 161. In Part II of the same paper he examined the high temperature behavior and listed a “Life Factor” for the joint (until lcikagc) that was equal to the ratio of th component sum of the initial elastic strains divided by the suni of the component creep strains, multiplied by the stress relaxation relationship outlined in Figure 2. The method outlined was based on the assumption that the joint life was determined by the relative component deformation (both elastic and creep).