Industry – UK Nuclear Power Generation
A nuclear power station producing 1000 MW requires in the region of 150,000 m3 of cooling water per hour when active. The flow is regulated by the Main Cooling Water (MCW) Valves, which throttle the supply. As a result of this duty, the valves can be damaged by the effects of the constant water flow & cavitation.
The client had removed 4 of these 66” MCW valves and sent them to Pump Group for refurbishment. The butterfly valves had previously been coated by others, and it was clear to see that there was extensive damage to the valve. Pump Group had previously used Belzona® 2141 Anti-Cavitation polymer to coat the pipes immediately downstream of the valve; as the client was happy with the performance of the Belzona they elected to use it on the valves.
On arrival the valves were disassembled and inspected fully. The pressure side of the valve was worn but in reasonable condition, however the downstream side had suffered major cavitation damage. The existing coating had worn away completely near the leading edge, allowing substantial damage to occur to the metal due to the Corrosion – Erosion cycle.
The existing coating was fully removed in our workshop then the base metal was hot chemical washed prior to being grit blasted. Once the surface profile was grit blasted to surface preparation specification SA 2.5 (75 micron surface profile), the metal was then tested to ensure salts and nitrates present were less than 3ppm concentration. This is to ensure that the Belzona polymer bonds correctly to the substrate correctly.
Belzona® 1111 Super Metal was used to rebuild the severely worn areas to the original profile. On the upstream side, 4 x 250 micron coats of Belzona® 1321 Super Metal were applied. This side of the valve doesn’t have to be protected from cavitation, so a coating was selected to increase efficiency, whilst still offering long lasting protection against erosion/corrosion from the sea water. Another advantage of 1321 is that it has very high compressive strength, making it ideal for use on the upstream side of the valve. On the non-pressure side, 3 x 1000 micron coats of Belzona® 2141 ACR-Fluid Elastomer coating were used. The high elasticity of this polymer is perfect for combatting cavitation; nullifying the damaging effects from the shockwaves created by the collapsing bubbles.
In addition to the Belzona coatings, the drive shafts, bush bearings & nylon shims were manufactured and replaced, and the pin locations were bored out to new size. New drive shafts, shear pins & locking pins were reverse engineered and manufactured from 431 Stainless Steel in house, and fitted along with new bearings, Devlon thrust washers & other consumables.
The valves were assembled and hydrostatically pressure tested to 1.5 times their working pressure.
The total turnaround time for the 4 valves was inside 10 weeks from receipt of the go-ahead, at less than half the cost of new and with the added benefit of a coating providing enhanced wear properties when compared to the parent metal.
For more information on how Pump Group can utilise Belzona coatings to assist with your operational needs – please contact our Repairs Team on 0161 864 4678 or via email@example.com