Case Study

Butterfly Valves: Pitting and Cavitation Protection



Challenge

EDF Energy requested the manufacture and corrosion protection, against pitting and cavitation, of 2 1600mm NB butterfly valves to extend their service life. In service, at Toreness Nuclear Power Station, the CW valves would be subject to constant exposure to sea water.

Solution

The body and blade of the butterfly valves were cast using BS3100: Grade A1 cast steel. The shafts were manufactured using BS970-431-S29 high strength stainless steel. Following suitable surface preparation the blades were coated with Corroglass 600 to a minimum DFT of 1500μm and when cured were thickness and spark tested. The shafts were also protected against corrosion using Corrocoat Armagel to prevent any pitting corrosion in service. Armagel is suitable for immersed environments where good resistance to chemical attack combined with resistance to abrasion are requires such as pipes, chutes, process tanks, valves , etc. The bodies of the valves were also suitably prepared before being coated with multiple coats of Plasmet HTE to a minimum m DFT of 1500μm, HTE is used in areas requiring abrasion (and chemical) resistance. A topcoat of Corroglass EB was then applied to reach a total DFT of 2500μm. Corrocoat EB is ideally suited for brush application to areas subjected to sea-water or other aqueous immersion. The coating also provides good cavitation resistance. In order to provide all round protection the external surfaces of the valves were coated with Plasmet ZF, a surface tolerant coating, before a final coat of Corrothane AP1 was applied.

Full Corrosion Protection

After curing the valve body and blade were thickness and spark tested to identify any holidays and ensure the professional quality of the coating work. Coating the valve with specialist protective coatings will significantly increase the expected service life and protect the valves exposure to seawater and from pitting and cavitation corrosion in particular. 1: Newly cast butterfly valve body. 2: Newly cast blades. 3: Body & blades post abrasive blasting. 4: Spray coating of blades. 5: Hand application of EB to valve body. 6: Completed valve blade. 7: Completed, corrosion protected, valve body.

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