Rubber lining a pitted and or corroded tank can be a challenge at the best of times…
There are many considerations in order to evaluate what materials to use. The most important part of repair, re-line, remediation of a tank is to have a good clean surface.
Blasting the sub-straight to a near white metal is important to remove, dirt, scale, residual chemicals which would all affect adhesion to the sub-straight. After blasting you can also determine the amount of good steel left. Many times repairs will need to be done in the most problematical area’s.
Once the sub-straight has been deemed sound all slag, debris blasting media must be removed and thoroughly cleaned. Suction companies are readily used in order to remove waste materials. Note when cleaning with solvents ensure the solvents are compatible with the adhesive system being used. For more reference on this see the post on Toluene and Trichloroehtylene.
Also note that dehumidifiers, heaters and hording of the tank are important in order to control the internal temperatures and climate to avoid flash rusting subsequent to blast.
After the sub-straight is clean you have to decide if you will fill in all the voids. There are several ways and materials you can choose. Bondo has been used, epoxy fillers such as Devcons have been used and ultimately as long as the filler used is stable over time, adheres to the sub-straight and is spread extremely smoothly and you can get a nice final finish, than you can use it to fill in the voids. The reason you need to fill the voids is if you use pre-cured sheet rubber for your application than the amount of surface the backing will be in contact with can be as little as 30%. By filling in the voids you can have 90-100% of the backing surface being properly adhered.
The next part of this equation is what method of lining and curing to choose.
1- The best possible liner you can put into a tank is a raw rubber liner that gets vulcanized after installation.
Pro’s
-Raw un-cured rubber has good malleability in order to get into all the scaling crevasses.
-You will get the best adhesion using uncured rubber.
-Ultimately an installed and cured liner will have more homogeneous seems.
Cons’s
-Small tanks are the only practical sizes for this type of rubber application
-Rubber cures in sun and in UV, depending on site conditions and storage, the top layers may cure while waiting to be installed, you may lose rubber square footage depending on your application time and conditions.
-Any pits not filled with an epoxy can be prone to blistering as the air trapped in hole will expand during the cure and may set that way.
-The limitation of course of this type of lining style is the availability size of your boiler. ex. 60′ X 65′ Dia. high tank would require a 300 HP boiler to overcome the heat loss of a hoarded tank. The boiler would consuming approx a swimming pools worth of diesel in order to provide a 24 H cure.
2- The most common method of handling tanks is using cured rubber.
Pro’s
-The rubber can not go bad on site.
-You save all the curing time, diesel costs, hording, setup for the cure.
Cons’s
-You must buff the backing or have the backing pre-buffed for good adhesion to the sub-straight.
-Adhesion to the sub-straight is more difficult as the rubber is rigid. Extra time needed for good stitching to ensure proper adhesion.
3- The least desirable are the chemical cure liners.
Pro’s
-You get to use semi-uncured material which is generally easier to line with.
-You will get better adhesion to the surface.
Cons’s
-After the initial chemical kick for curing the liner takes approx 18 days for a full cure. People are generally in a rush to add the liquid back into the tank. Filling the tank prior to the full cure will halt the cure and you may not get durometer or the intended performance out of the rubber required.
4- Using uncured rubber and curing the rubber using hot water.
Pro’s
-Raw un-cured rubber has good malleability in order to get into all the scaling crevasse.
-You will get the best adhesion using uncured rubber.
-The rubber will cure very consistently.
Cons’s
-Difficult to get that large of a volume of water.
-Heating that much water requires alot of energy, and that can get very expensive.
As you may have noticed we did not go over any of the nuances of lining on site. We focused primarily on the types of method applications and none of the health and safety, site requirements unique to every site.
In the end lining a corroded tank is not for the faint at heart. It requires years of field experience in order to perform these jobs on time and on budget.
