What lies beneath – Plant Room Slab Corrosion
By: A. L. Airey, Airey Taylor Consulting
Synopsis: This paper discusses mechanisms of corrosion found in plant rooms as published in the project profile “Problems with Plant Rooms” in the October 2010 issue of Corrosion & Materials with additional details of the electropotential surveys and other case materials. Plant room slabs can experience sheet-style delamination as a first sign that maintenance is required. This issue relates to their purpose, housing a concentrated array of mechanical/electrical and plumbing fittings, in combination with aggressive conditions relating to use of cooling tower chemicals. Common mechanisms of corrosion initiation include the leakage and “windage losses” of treatment chemicals and brackish water concentrates sprayed onto the slab and surrounding metal items. Copper pipes in direct contact with slabs subject to wetting are also a cause of aggressive galvanic corrosion with reinforcement donating electrons to copper. Diagnosis of the extent of corrosion is explored in a case study using electro-potential mapping, with the finding that a 50% corrosion probability related to in-situ corrosion confirmed during breakout. A repair case study and the rationale behind it from a structural perspective is given. The inadvisability of relying on patch repair strategies is discussed. Given the likelihood of future maintenance well within the 50 year lifespan of the building, some observations are made on the placement of plant room slabs enabling maintenance inspections.
The first page of the paper is available here; with more information available from Airey Taylor Consulting on request.
