Are you searching for “FRP Storage Tank Linings VS Replacing Steel Tank Bottoms?” If so you are probably trying to decide if it is better to get a linking, or replace the bottom of your steel tank. There are a lot of chemicals that can be really corrosive to any above ground metal storage tanks, which can result in a leak. The normal corrosion rate for many carbon-steel storage tanks in certain temperatures is more than 1 mil per year, with a leak happening in less than 5 years. These leaks will often result in costs for environmental penalties and tank repair.
Tank corrosion can also increase whenever there is a layer of water that is containing soluble chlorides and salts that settle at the bottom. These compounds are considered highly corrosive to begin with, but they can also generate strong electrolytes that will cause corrosion from within. There can also be an issue with external tank corrosion too. The bottoms of above ground storage tanks are quite susceptible to various types of corrosion, especially if the tanks are subjected to stray electrical currents in soil or are close to salt water.
If the above ground tank bottom is corroding, it will need to be coated with a thick film FRP or fiberglass reinforced plastic that has about a 65 mil dry film thickness or be replaced. Since replacing the tank bottom can be time consuming and expensive, FRP linings have really become a popular solution for tank bottom repair.
FRP Lining Installation
This recent trend has a lot of places shifting away from just replacing the tank bottom and moving towards the FRP lining system. Installing the lining system means that you have to apply primer, putty, a catalyzed resin that has a glass mat and then a seal coat. The tank has to be dry and the surface must be fully prepared. The whole process is a lot quicker and less costly than replacing the tank bottom.
The FRP lining is considered to be a secondary bottom that is bonded tightly to the storage tank. Whenever it is properly applied, it will prevent any leakage because of internal corrosion for about 20 years. If the supporting steel bottom becomes perforated, the lining will help to minimize the issue of exterior corrosion by giving it strength to bridge the small perforation. Even if there is severe corrosion on the outside, it may be possible to apply a double layer for a thickness of around 120 mil. A lining that is less than 20 mil when dry will not be able to protect against leakage. It is recommended at that for new tanks that have no underside corrosion or pitting.
Introduced in the 1950s, FPR laminates were made from orthophthalic polyesters that would bridge gaps caused by corrosion and were thought to protect from internal corrosion. Although in the 1960s, it was found that isophthalic polyester resin was better to withstand corrosion. Vinyl ester resin was founded in mid-1960s and performed great, but it was so expensive that it was only used when high performance was needed. Now, FRP linings are made of epoxy novolacin vinyl ester.
Just like with any repair, FPR linings will have its disadvantages and advantages.
- For most installations, FRP linings will have a 35+ year service history.
- FRP linings are less expensive than replacing a steel tank bottom.
- FRP linings are quickly installed, minimize down time, and work better than replacing the bottom of the tank.
- FRP linings that have vinyl ester resin can resist various corrosive things at high temperatures.
- FRP linings can bridge a hole up to 8 inches in diameter and a double laminate can withstand 82psi while single laminates can handle 37psi.
- Cyclic loading could affect the ability of FRP Linings to bridge a clear, large opening, the extent of effect hasn’t been known yet.
- Whenever a pigmented gel coat is used, you cannot see the bottom to find the extent of the corrosion. Although, new technology and high power magnets can now scan laminates to find information about the corrosion.
- The applicator must be aware of the installation procedures and the importance of contaminant free substrates before applying.
Standing Up to Pressure
There haven’t been a lot of articles about FRP laminates that talk about the pros and cons of being used instead of replacing a steel tank bottom. There was a case that describe a 211ft diameter tank that had FPR laminate installed in 1985. During 1995 a leak started in the sump area which was caused by bottom side corrosion. 2 holes had been created, each about a foot wide. Although, it was determined that the FPR lining didn’t fail. It was the lining that was actually containing the contents of the tank and it did until hydraulic pressure caused it to bust.
Now you may be asking just how much pressure can the lining stand? A physical pressure test was done in a water filled chamber that would let steam be pumped into a pipe loop until it hit 140 degrees. 8 plates of 12* ¥ 11/2* ¥ 4* steel were made with a set of holes cut in the middle of the plates to represent corrosion. The holes ranged in diameter and were filled with melted wax and isophthalic polyester laminate on top. Just a single laminate was used on 1 set of the plates while double laminates on the other. A deflection gauge was installed on the bottom to measure the deflection amount.
Although there were some failures on one of the plates at 28psi for single laminate and 66psi on double laminate, this was caused by mistakes in the steel fabrication. None of the edges had been radius, the laminates were shoved into the holes, which caused it to fail.
A new test was done and 4 new plates were made that had edges. 2 were done with single laminates and the other were with double laminates. The single laminates did better in the second test with 37psi before the laminate went through the hole. While the double laminate held until 82psi.
According to the tests, it is assumed that bottom side corrosion won’t happen with sharp edges and that it will be gradual, so it is assumed that FRP linings will contain the contents of the storage tank where the internal pressure doesn’t exceed 37psi for single and 82psi for double. Since 22psi happens to be a typical internal pressure, it would seem that FRP linings will offer a margin of safety for internal hydraulic pressure.
An important alternative to having to replace a steel tank bottom is the Thick film FRP lining system which will mitigate external and internal corrosion. Based on the applications over the years, it would a proven history of being successful. While using FRP lining systems have their disadvantages and advantages, one main advantage is the test results that have measured the performance under hydraulic pressure.
Phoenix Tank Lining Company
If you are looking for the highest quality tank linings for your FRP and steel tanks in the Phoenix metro area All Kote Lining, Inc. can handle all of your needs. We take care of linings and tank restorations for companies both big and small and no job is too large or little. We are punctual, professional, and provide the highest quality tank linings available. If you have tanks that have some damage, need regular maintenance, or need an overhaul call All Kote Lining today for service by calling 480-966-4446.