Flange bolting on nuclear steam non‑return valve

Problem

Due to high pressure on start-up the valve was suffering from heavy flange rotation. This reduced the gasket contact area by 50% and a few days after start-up, the joint would leak. The customer estimated annual repair costs of £15,000.

Application

Mannesmann steam valve

Pressure: 160 bar (16 MPa)

Operating temperature: 300°C (572°F)

Studs: 200 off 3" x 580 mm, material B7

Method of tightening: torque

Design load/stud: 150 tonnes

Gasket configuration: Kammprofile (material SS316 + SPG)

Existing solution

Several types of gasket were tried and tested by the customer to eliminate the leakage.

James Walker solution

The James Walker team undertook a flange management assessment, which led to a redesign of the gasket, replacing the kammprofile with a spiral wound gasket, as well as the addition of a secondary seal and the implementation of RotaBolt RB2 Touch. The RotaBolt RB2 Touch ensures bolts are installed to the correct tension and offers a simple tactile check this is being successfully maintained. It features two tension settings within a single sensor for greater control and monitoring, so is ideal for applications such as this, where the rotation of the flange was proving problematic.

Results and benefits

• Start-up leakage eliminated
• Improved operational efficiency due to reduced downtime
• Reduced maintenance due to simple tension monitoring

After the installation of RotaBolt RB2 Touch, the customer reported a 100% leak free start up rate. So successful was the implementation that the customer commissioned the services of James Walker to install RotaBolt technology on a second nuclear power plant experiencing the same issues.