National Grid is seeking to respond to a set of valve related problems, initially thought to be caused by the widespread ingress of water into valve stem extension assemblies. This water ingress can lead to:

• Internal corrosion of the torque tube and of the valve stem.
• Corrosion debris fouling the lower quadrant mechanism.
• Internal seal/flange damage.These effects can lead to failure of the valve to operate on demand having serious implications on the safe management of the National Transmission System (NTS).This water ingress is likely to come from one or more of:
• Weather seal failure on the actuator or stem. • Rain water entry through the breather / vent cap or vent hole (where the vent plug has been removed or damaged).
• Condensation inside the valve stem accumulating in the bottom until it fills up.
• Through a combination of a high water table and a leaking bottom flange.

The annulus between the stem and the torque tubing, with a ready supply of water, oxygen and untreated metal, is therefore an ideal environment for corrosion to occur.

Periodic inspection is carried out on the valves every 12 months (critical infrastructure) or 24 months (noncritical). This work usually starts with closure of the valves and a vent down of the system; if the valves are passing and the pressure cannot be bled off this indicates that a valve is passing. This may be due to incomplete valve closure.

The full spectrum of valve failure scenarios that could be caused by corrosion in torque tubes is very broad. It is extremely unlikely that a single solution will be appropriate for all cases, and inconceivable that any such solution will be universally applicable. With the Valve Care Toolbox approach, there will be a number of engineering solutions available thus improving the effectiveness of the remedial actions taken.

Benefits

The programme has been structured (via a Work Package (WP) Stage Gates) to ensure the respective benefits outlined below are demonstrated:

WP1: Confirm the challenges of the solution and develop a screening process to choose the most appropriate techniques to move forward.the respective benefits outlined below are demonstrated:

WP2: Provide a full view of potential solutions (idea generation) and outline a long list of solutions (initial screening).the respective benefits outlined below are demonstrated:

WP3: Carry out an Engineering Screening Process to determine the initial feasibility of the long list of solutions.the respective benefits outlined below are demonstrated:

WP4: Recommend an initial list of solutions to be taken forward with appropriate costs.the respective benefits outlined below are demonstrated:

WP5: Validate and Test initial concept ideas.