Behaviour of Compressed Asbestos-Fibre Gaskets in Narrow-Faced, Bolted, Flanged Joints

Abstract

In an attempt to establish the conditions necessary to maintain ‘tightness’ in narrow-faced, bolted, flanged joints, experiments were carried out on standard 300 lb. per sq. in., 900 deg. F. screwed-on and welded-on flanges fitted to 2 1/2-inch bore pipes. ‘Klingerit’, rubber-bonded asbestos, gaskets of various dimensions were tested. Stresses in the bolts were measured by means of electrical resistance strain-gauges. The pressure fluid used was water. The screwed-on flanges were later turned down to approximately half their original thickness to determine the effect of flange thickness on leakage pressure. Photo-elastic studies were carried out to determine the distribution of axial stress in the gasket due to bolting up. The following points were established: (1a) The gasket factor, m, of compressed asbestos jointing increases practically linearly with gasket thickness. This is the opposite of the trend of the values given in the A.S.M.E. Unifired Pressure Vessel Code of 1952 (A.S.M.E. 1952). (1b) The gasket factor of compressed asbestos jointing increases with decreased gasket width. (2) The gasket yielding pressure, y, of compressed asbestos jointing is, for water as pressure fluid, independent of gasket dimensions. (3) Bolt stress may increase, decrease, or remain constant during increase in internal pressure, in one and the same joint, depending only on the initial bolt stress. (4) The centre of gasket reaction is situated closer to the outer edge of the gasket than to the inner; the exact position depending on the relative stiffness of the flange and gasket material. (5) Increasing thickness or decreasing width or external diameter of the gasket reduces the pressure which the joint is capable of containing. (6) Reducing the thickness of the flange ring increases the gasket stress necessary to contain any particular internal pressure.