Originally Posted by steve-ribnet
I'm amazed- plastic really?? I was going to replace with stainless- why plastic over stainless? This is a 90 litre tank. The battery tray sits on it and various cables pass over and down the side of it- I would worry about chafing a plastic tank ...
I had a 60 gallon aluminium gasoline tank. It developed holes. The areas near the holes were also wafer/paper thin.
Now have a plastic one.
Remember to have the uplift pipes at the stern of the tank. When riding even slightly bow up (when nearing and empty tank the fuel 'collects at the back. If you have the fuel uplifts at the bow you do not get to use all the fuel when planing.
Remember also stainless steel is just that 'Stain less
' not 'stain free' or 'corrosion free'. Stainless steel also suffers from pocket or crevice corrosion (lack of oxygen).
Types of Stainless Corrosion
According to the DOD Technical Bulletin Corrosion Detection and Prevention there are 8 separate types of corrosion, with only a few having a major impact on stainless steel. Please be advised the descriptions below are extremely brief and written in laymen terms. Before acting on any particular application, qualified advice particular to such application should be obtained.
1. Uniform Attack
- also known as general corrosion, this type of corrosion occurs when there is an overall breakdown of the passive film. The entire surface of the metal will show a uniform sponge like appearance. Halogens penetrate the passive film of stainless and allow corrosion to occur. These halogens are easily recognizable, because they end with "-ine". Fluorine, chlorine, bromine, iodine and astatine are some of the most active.
2. Crevice Corrosion
- this is a problem with stainless fasteners used in seawater applications, because of the low PH of salt water. Chlorides pit the passivated surface, where the low PH saltwater attacks the exposed metal. Lacking the oxygen to re-passivate, corrosion continues. As is signified by its name, this corrosion is most common in oxygen restricted crevices, such as under a bolt head.
- See Galvanic Corrosion. Stainless that had had its passivation penetrated in a small spot becomes an anodic, with the passivated part remaining a cathodic, causing a pit type corrosion.
4. Galvanic Corrosion
- Placing 2 dissimilar metals in a electrolyte produces an electrical current. A battery incorporates this simple philosophy in a controlled environment. The current flows from the anodic metal and towards the cathodic metal, and in the process slowly removes material from the anodic metal. Seawater makes a good electrolyte, and thus, galvanic corrosion is a common problem in this environment. 18-8 series stainless fasteners that work fine on fresh water boats, may experience accelerated galvanic corrosion in seawater boats, and thus it is suggested you examine 316 stainless.