BACTERIAL CORROSION
Colonies of bacteria from corrosion. Black gelatinous protuberances in area in contact with the metal plate (sulfate-reducing bacteria) and reddish-brown color on this (iron bacteria).
The corrosion of carbon steel elements caused by anaerobic bacteria is common in installations exposed to water extracted from deep wells in northern Chile. The bacteria that causes corrosion to steel corresponds to the sulfate-reducing bacteria, which is usually accompanied by iron bacteria. The environment conducive to its development, that is, absence of oxygen, sulphated waters and pH between 5.5 and 8, triggers the localized and harmful corrosive action. Thus, in the inner bottom of drinking water tanks, colonies of bacteria were detected in the form of black gelatinous protuberances on the inside and reddish brown on the outside, causing severe corrosion and damage to the steel.
The repair and subsequent anticorrosive protection of metal structures that are damaged by bacterial corrosion, require to eliminate any trace of bacterial development by means of a deep mechanical treatment, washing and scrubbing with a caustic soda solution and thorough rinsing until reaching pH7 and eliminating any excess of cleaning products. Allow to dry and treat with white metal blast cleaning (SSPC-SP5). Indentations greater than 1 mm should be primed with a brush and covered with an epoxy filler until making up to metal surface. The characteristics of both, the primer and the epoxy filler should be determined according to the area and working condition. If the structural analysis suggested to reinforce part or all the surface involved, repaired engineering should be considered. The anticorrosive protection design should consider the use of a studied coating system, together with a cathodic protection system. The selected designs must be compatible with each other, meet the environment requirements and those for an optimal application.
Corrosion by bacteria in pond botton