138” Turbine Inlet Valve Replacement Disc Design
Background
eTec were employed to support the refurbishment of a 138” butterfly valve for a hydro station in Scotland which had been in service since 1930 and was presenting the operator with isolation difficulties.
The valve had a lenticular cast disc with a metal to metal seat, operated by twin hydraulic cylinders.
The Problem
After dismantling, detailed inspection showed substantial cracks within the disc. Various repair options such as welding, mechanical bracing etc. were explored and ruled out due to potential risk to programme and concerns regarding the integrity of the repair. In addition, the existing metal to metal seal design was prone to high leakage rendering difficulty to achieve isolation for Turbine maintenance.
The option of an identical replacement disc casting was explored but lead times could not be accommodated within the outage programme.
The Solution
The main contractor RWE Power International employed eTec to provide design, engineering support and QA Inspection for a replacement disc.
Based on eTec experience, a fabricated disc was provided to achieve programme deadlines with the design validated using FE analysis. In addition to providing a design that could be manufactured within the time available, shaft and sealing arrangements were redesigned which both improved the design and reduced costs.
The design developed by eTec incorporated a resilient sealing arrangement. This type of seal allowed the entire periphery of the disc to seal against the existing metal body seat. The new seal design also permits site adjustment to achieve leak tightness which was not possible on the previous metal to metal design.
The fabricated disc and resilient seal was successfully manufactured and works tested using the existing hydraulic actuators to operate valve