Re: Fibreboard under the tank bottom plateFrom: CNT 
Date: Friday, March 09, 2012
Time: 9:25:05 AM
Remote Name: 184.108.40.206
CommentsWith the recommended Drip Ring that API 650 now includes, which is an extension of the floor extension that extends past and then down over the edge of the ringwall should eliminate any need for the fiberboard and should eliminate the water infiltration issues assuming the water in the dike stays below the top of the ringwall. Ive not seen anyone install the drip ring, but it seems like a good idea that would actually solve the water infiltration issue. The use of caulking or asphalt board never seems to hold up long term. All of the systems Ive seen eventually fail, allowing water to infiltrate under the tank.
And then there is the ground water that could potentially be infiltrating up from underneath on the inside of the ringwall. I think that putting an asphalt board or caulking the area probably helps some, but doing so and then considering the area under the tank to be dry is naive.