Abstract
In the CEGB, boilers are cleaned periodically to remove from the boiler tubes accumulations of magnetite and feed-borne debris which might ultimately lead to corrosion if left undisturbed. A criterion for the timing of such cleans has been evolved based on the measurement of oxide thickness. Composition and regularity of the oxide may also be taken into account in marginal cases.
Chemical cleaning itself causes metal losses, either directly, by residual corrosion in the presence of inhibitor, or indirectly, by removing protective oxide which then has to be re-established from base metal. The cumulative metal losses likely to arise from periodic cleaning of mild steel boilers have, therefore, been evaluated from data on oxide thickness formed in service and the corrosion rates of the underlying metals measured in inhibited acid. The evaluation shows that, for an allowable 5% loss in tube wall thickness from this cause, most conventional plant can be cleaned up to 10 times during its life time, which is compatible with actual requirements.
Get full access to this article
View all access options for this article.