A leading manufacturer of sub-sea isolation valves planned to install upper and lower completions in a challenging deep-water environment. An isolation barrier valve was used in order to isolate the reservoirs before running the upper completions. This required increased force in the assembly to open/close the seal faces of the in-line ball valve operating in sub-sea conditions. With axial and radial space at an absolute premium, the use of conventional disc spring packs or helical coil springs was not an option.
A Smalley Crest-to-Crest® flat wire wave spring was chosen to solve the problem but, because the force required at operating height could not be achieved with a single spring, an interlaced design was recommended. An interlaced spring is formed from two or three constituent wave springs of similar thickness, amplitude and frequency combined so that the springs turn about each other for the entire length of the spring. The interlacing effectively increases the thickness of the flat wire section thereby providing increased loading capability.
In the hostile environment in which the springs were likely to be operating, very high temperatures could potentially be reached, and attacks by sour gas, salt and seawater were likely. This meant that Inconel X-750 material was chosen for the application. Inconel not only has a high resistance to corrosion but also offers a reasonably high tensile property. This allowed TFC˜s engineers to solve the customers™ corrosion challenge and keep the spring close to the same size as a standard material alloy spring.
The unique features of the TFC Smalley interlaced spring meant the customer was able to improve the sealing efficiency of the valve and greatly optimise the use of the axial and radial space provided by the narrow wall sectioned TFC spring.