For Cryogenic valves clinet has a requirement for the "Collar rings" at the extended bonnets. As far as I am aware, collar (drip) rings are used to terminate the insulation around the valve, specifically the bonnet, after intallation. They are a flat disc that surrounds the extended bonnet, with the plane of the disc normal to the axis of the bonnet/stem. The diameter and, to a lesser extent, the position of the collar ring needs to be specified by the client. From memory the collar ring is normally about 100 mm / 4" above the joint of the bonnet to the valve in order to provide reasonable access to the flange bolting. However, check with the client!Normally they are welded on but with the extended bonnet being a pressure containing component the weld will be classified as a pressure containing weld, with all the certification that that includes.

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