Experimental investigation on bolt tension of flanged pipe joint subjected to bending

Abstract

Analysis of a flanged pipe joint subjected to bending and determination of maximum bolt tension is a rather difficult task due to absence of a rational method of analysis. Conventionally, in absence of specific guideline or code provisions, a method analogous to beam flexure is adopted to determine the bolt tension. It is assumed that bolt force (tension or compression) is linearly proportional to the distance from the neutral axis. But this methodology may not always give the accurate result since the assumptions made are not practically valid. In this experimental research, an investigation has been made to find out the effect of various parameters relating to flanged pipe joint connection. To carry out the investigation, 36 flanged pipe joint specimens are prepared using 125 mm, 150 mm and 200 mm diameter pipe. Flanges are made from different thickness (6mm to 24mm) of mild steel plates having 30 mm, 36 mm and 48mm width. Flanges are connected using ASTM A325M bolts of 10 mm, 12 mm and 16 mm diameter. Flange is connected to the pipe using slip on flange method. During experiment two points load is applied by a custom made load spreader using the universal testing machine. To measure bolt force special strain gauge BTM-6C is inserted inside bolt shank and reading is taken using data logger. The pipe joint has been subjected to moment by applying force at a certain distance from the flange joint and under this moment the maximum bolt tension has been measured. Based on analysis of experimental results it may be suggested that for a flanged pipe joint subjected to pure bending moment, when flange thickness is same as pipe thickness bolt tension value obtained from conventional analysis should be doubled to obtain a reasonable estimate of bolt tension. When flange thickness is thrice the pipe thickness bolt tension calculated by conventional method may be assumed reasonable. For intermediate thickness of flange a linear interpolation may be performed.