Flange Bolting Washers are the heat and corrosion resistant washers that compensate loosing of pre-tightening force between flange and bolt with the property "small deformation, huge compensation force". The washers are designed to provide added holding power in the absence of a flat washer, essentially taking its place. One of the most popular uses is in pipefitting and plumbing. Comparing with bellvilles, flange bolting washers last longer life and will reduce and the amount of maintenance required.
Why the pre-tightening force goes to loose?
expanding with heat and contracting with cold
increasing or decreasing of the pressure,then the flange and gasket will be out of shape
shocking of the equipments.
If we install the washers between flange and bolt, it will be like this: