The Behaviour of Narrow-Faced,Bolted,Flanged Joints under the Influence of Internal Pressure

Abstract

A narrow-faced, bolted, flanged joint is a highly complicated stress-system. When internal pressure is applied, the stress-system changes. In order to establish, quantitatively, what these changes are, a series of experiments were carried out on a pair of -in. nominal bore screw-on hubbed flanges.

The apparatus was assembled as shown in Donald and Salomon (1, Fig. 1)† An accurate measure of bolt stress and, hence, the stress on the gasket was obtained by attaching a total of four electric resistance strain-gauges to two ‘measuring’ bolts. As the nuts were all tightened carefully by means of a torsion wrench, an average of the readings of the four gauges gave the average bolt stress of the eight bolts.

Care was taken that the gauges were cemented to diametrically opposite sides of the bolts and that two of the gauges were pointing toward the centre of the flange while the other two were pointing in the opposite direction. From the readings of the two pairs of strain-gauges, it was possible to calculate the extent of bending of the bolts during application of internal pressure and, hence, the rotation of the flange-rings due to pressure. The results of the experiments indicated:

1. (1)

• (a)

There is a linear relationship between bolt load and internal pressure.

(b)

The slope of the line giving this relationship depends on the elastic properties and the dimensions of the components of the joint.

(c)

This slope can be predicted mathematically.

(d)

This slope can, in the case of pseudo-elastic gasket materials such as compressed asbestos composition, be positive, negative, or zero; the slope in any particular joint depending only on the initial load on the gasket.

(2)

• (a)

The rotation of the flange rings due to pressure increases as the slope of the bolt load versus internal pressure line changes from negative to positive.

(b)

The rotation, as calculated from strain-gauge measurements agrees fairly well with that calculated by use of the theory of Wesstrom and Bergh.

(3)

The circumferential strain in the flange and pipe assembly is at a maximum in the pipe at the back of the hub. This result is in agreement with that reported by several other investigators and is not discussed in this paper.